GEOCHEMISTRY OF TRACE ELEMENTS IN THE BOLIVIAN

Transcription

GEOCHEMISTRY OF TRACE ELEMENTS
IN THE BOLIVIAN ALTIPLANO
Effects of natural processes and anthropogenic activities
Oswaldo Eduardo Ramos Ramos
June 2014
TRITA-LWR PHD-2014:04
ISSN 1650-8602
ISBN 978-91-7595-177-5
TRITA LWR PHD-2014:04
Cover illustration:
Top left: Lake Poopó landscape; Top right: Machacamarquita mine; Botton left: sediment of thermal water;
Botton center: waste material in the Tiwanaku tailing (Photograph: Prosun Bhattacharya ©, 2009); Botton right:
model concept of trace elements in Poopó Basin (Figure: Oswaldo Eduardo Ramos Ramos©, 2014).
© Oswaldo Eduardo Ramos Ramos 2014
PhD Thesis
KTH-International Groundwater Arsenic Research Group
Division of Land and Water Resources Engineering
Department of Sustainable Development, Environmental Science and Engineering (SEED)
KTH Royal Institute of Technology
SE-100 44 STOCKHOLM, Sweden
Reference to this publication should be written as: Ramos Ramos, O. E. (2014) “Geochemistry of
trace elements in the Bolivian Altiplano - Effects of natural processes and anthropogenic activities”.
PhD Thesis, TRITA LWR PHD-2014:04
ii
Geochemistry of trace elements in the Bolivian Altiplano
Dedicated to Zaret Astrid, Leonardo Fabian and Brenda Alison
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F OREWORD
The thesis deals with the levels of trace metals and their mobility in the Bolivian Altiplano and aims at an evaluation of the risk for human exposure via different pathways, such as drinking water and food items. The area is affected by long term mining activities, covering hundreds of years from precolonial time until present day.
The production of metals like tin, silver, lead and zinc is still a major share of the Bolivian economy and is likely to remain so. The thesis deals with a multitude of matrixes, like surface water, groundwater, agricultural soils, crops, and lake sediments in
order to evaluate the risk of mobilizing metals which might threaten the human
health. An extensive literature survey has been done to set the conditions in relation
to notably the South American conditions. The geology of the Titicaca region, part
of the Bolivian Altiplano is complex and constitutes an important background for
the study. Not only the mining activities are governing the behaviour of trace metals
as the mineral deposits are present in different host rocks determining the pH and
redox conditions of the terrestrial and aquatic environments. Regarding trace metals I
surface water sampling and analysis has been done from headwater areas, above the
mining areas down to the Poopó basin. Arsenic, cadmium, manganese and zinc concentrations in surface water exceed the WHO guidelines in some of the streams. The
presence of iron hydroxyoxides provides a control of the arsenic content in groundwater as they are excellent adsorbents for arsenic under oxidizing conditions which is
revealed by sequential extraction. DTPA extraction has been used to assess the plant
availability of trace metals in soils. The investigation of crops has revealed that arsenic and cadmium do not exceed guideline but that lead does so in beans and potatoes. The computer code PHREEQC has been used to study trace metal species and
possible equilibria with solid phases. A particular magnesium arsenate has been detected in the mineralogical studies of soils. A number of approaches has been used to
assess the environmental risk of trace metals such as RAC (Risk Assessment Code),
Igeo (Geoaccumulation ratio) and EF (Metal Enrichement Factor). In conclusion is
turn out that the behaviour of arsenic requires further studies in relation to the hydrogeological conditions. The bioavailability in crops of different trace metals species, inorganic and organic deserve further attention.
Prof. Em. Gunnar Jacks
Stockholm, KTH, June 2014
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A CKNOWLEDGEMENTS
I would like to express my sincere gratitude to Sida/SAREC for financial support,
which has made this research possible and has contributed significantly to the capacity building at Universidad Mayor de San Andrés (UMSA), also to Swedish International (SI) and International Science Programme (ISP) in Sweden and DIPGIS at
Universidad Mayor de San Andrés in Bolivia for administrative assistance, coordination and management of funds and scholarship.
This research was funded through the Swedish International Development Cooperation Agency in Bolivia (Sida Contribution: 7500707606) and also acknowledge the
support of the CAMINAR project (INCO-CT-2006-032539) funded by the International Cooperation section of the European Commission under the 6th Framework
Programme.
I greatly appreciate the coordination, supervision and support of Prof. Prosun
Bhattacharya, Prof. Roger Thunvik and Prof. Jorge Quintanilla that contributed
greatly to the success of PhD studies at KTH and UMSA, respectively.
I wish to extend profound gratitude to my supervisors Dr. Ondra Sracek and Dr.
Jochen Bundschuh for their scientific guidance and constructive inputs to my research papers. My gratitude also to Jyoti Prakash Maity for his revision of my thesis
and discussion, without his determined support and encouragement, I could not have
accomplished this thesis.
I am grateful to Prof. Gunnar Jacks at KTH for vigorous work in all the stages in lab
during the sequential extractions in soil, especially in the winter vacations 2009-2010,
and also for providing facilities and materials used for soils studies. I wish extend my
gratitude to all of my co-authors in the papers, without their scientific discussion and
input, I could not reach the publications of the scientific information. My special
thanks go to my friend (Mauricio, Amalia, Israel, Efrain, Mac, Elvira, and Liliana)
and colleagues (Zairis, Sandhi, Dipti, Ashis, Manoj, Tipu, Annaduzzaman, Anna and
Patricia) at both UMSA and KTH for the memories times in the field and lab work,
meal times and relax moments that I never ever forget. Special thanks are gratefully
extended to Annaduzzaman for helping me at the formatting stage of this thesis and
Mauricio for the meal times and fruitful discussion on groundwater chemistry.
My gratitude to Bertil, Anna, Monica for assistance in the lab analyses at KTH; and
also Aira, Britt and Jerzy for great assistance in administrative as well as health matters. I value the help from Prof. Carl-Magnus Mörth at the Department of Geological Sciences, Stockholm University for providing laboratory analysis.
My grateful to the administration staff at Universidad Mayor de San Andrés, Faculty
and Chemistry Department and Instituto de Investigaciones Químicas (IIQ) for
helping me to travel abroad without any trouble, particularly to Vice-Dean PhD Maria Eugenia Garcia.
My gratitude to my friends and colleagues Sulema, Rigoberto, and Luis Fernando at
Especialidades Químicas who through moral, spiritual support, comments and fruitful discussions during at stages of preparation of conferences, papers and this thesis.
My heartfelt thanks to my parents Albertina (R.I.P.), Adela (R.I.P.), Nestor, without
their guide, love and moral support I could not have been as I am today. My
acknowledgement to sister (Elba), brother (Ramiro), nephews and sisters and brothers in law are highly appreciated. My special grateful for my mother in law Teresa Villarroel for take care and love to my family during the travel to Sweden.
My especial thanks go to my children, Leonardo Fabian (five years old) and Zaret
Astrid (one year old), for understanding, patience and moral support during the travvii
els far away home. My sincere and profound gratitude is extended to my wife Brenda.
Her patience, love and constant encouragement in all the stages of this challenge,
particularly for understand me and moral support at times when I was wrote this
work.
Stockholm, June 2014
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L IST OF A PPENDED P APERS
Paper I
Ramos Ramos, O.E., Cáceres Choque, L.F., Ormachea, M., Bhattacharya, P., Quino, I.,
Quintanilla, J., Sracek, O., Thunvik, R., Bundschuh, J., García, M.E. 2012. Source and behavior of arsenic and trace elements in groundwater and surface water in the Poopó Lake Basin,
Bolivian Altipano. Environmental Earth. Sciences 66: 793-807. (Reprinted with permission from
Springer).
I participated in project designing, field work, collection of the samples and analyses, data
analysis and main part of writing.
Paper II
Ramos Ramos, O.E., Rötting T.S., French, M., Sracek, O., Quintanilla, J., Bundschuh, J.,
Bhattacharya, P. 2014. Hydrochemical characteristics of groundwater and surface water in
the mining region of Antequera and Poopó, Eastern Cordillera, Bolivian Altiplano. Manuscript.
I performed the project designing, collection of the samples in the field work, data analysis
and main part of writing.
Paper III
Ramos Ramos, O.E., Rötting, T.S., French, M., Sracek, O., Bundschuh, J., Quintanilla, J.,
Bhattacharya, P. Geochemical processes controlling mobilization of arsenic and trace elements in shallow aquifers and surface waters in the Antequera and Poopó mining regions,
Bolivian Altiplano. Journal of Hydrology (In review)
Paper IV
Ramos Ramos, O.E., Rötting, T.S., Orsag, V., Chambi, L., Sracek, O., Quintanilla, J.,
Bundschuh, J., Bhattacharya, P. 2014. Total and available trace elements concentrations in
soils and evaluation of uptake by crops in the mining area of the Bolivian Altiplano. Manuscript.
Paper V
Cáceres Choque, L.F., Ramos Ramos, O.E., Valdez, S.N., Choque R.R., Choque R.G.,
Férnandez, S.G., Sracek, O., Bhattacharya, P. 2013. Fractionation of heavy metals and assessment of contamination of the sediments of Lake Titicaca. Environmental Monitoring & Assessment 185: 9979-9994. (Reprinted with permission from Springer).
I performed the laboratory work, data analysis and main part of writing.
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T ABLE OF C ONTENTS
Foreword .................................................................................................................................. v
Acknowledgements ...............................................................................................................vii
List of Appended Papers ....................................................................................................... ix
Table of Contents .................................................................................................................. xi
ABSTRACT ............................................................................................................................. 1
1
Introduction ................................................................................................................... 1
2
3
1.1
3.1
Rationale ..................................................................................................................3
Research Objectives ...................................................................................................... 3
Background Literature .................................................................................................. 3
Trace elements and arsenic in the environment ......................................................4
3.1.1
3.1.2
3.1.3
Trace elements and arsenic in groundwater and surface water ..................................................... 4
Trace elements and arsenic in soils/ sediments ............................................................................... 5
Trace elements and arsenic in plants.................................................................................................. 6
3.2 Trace elements and arsenic in Latin America and Bolivia from natural and
anthropogenic sources........................................................................................................7
3.2.1
3.2.2
3.2.3
3.2.4
4
Study Area .................................................................................................................... 10
4.1
4.2
4.3
4.4
4.5
4.6
5
Argentina................................................................................................................................................. 7
Bolivia ...................................................................................................................................................... 7
Brazil ........................................................................................................................................................ 8
Chile ......................................................................................................................................................... 8
4.7
4.8
5.1
5.2
5.3
5.4
5.5
5.6
Study site description ............................................................................................. 10
4.1.1
4.1.2
4.1.3
4.1.4
Poopó Basin (PB) – (Paper I)............................................................................................................ 10
Antequera and Poopó Sub-basins – (Papers II and III) ............................................................... 10
Transects Coriviri, Ventaimedia, and Poopó – (Paper IV) .......................................................... 10
Titicaca Basin – (Paper V) ................................................................................................................. 11
Paleolakes development in northern and central Bolivian Altiplano ..................... 11
Geological settings ................................................................................................. 11
4.3.1
4.3.2
Geology around the Titicaca region ................................................................................................. 11
Oruro mineral deposits ...................................................................................................................... 12
Climate around the Bolivian Altiplano................................................................... 12
Hydrology in the Bolivian Altiplano ...................................................................... 13
4.5.1
4.5.2
4.5.3
Lake Titicaca.........................................................................................................................................13
Desaguadero River ..............................................................................................................................14
Lake Poopó ..........................................................................................................................................14
Source of salinity in shallow aquifers in Poopó Basin (PB) ................................... 14
4.6.1
4.6.2
Poopó Basin (PB) salinity in shallow aquifers ................................................................................ 14
Sub-basin (Antequera and Poopó) recharge ................................................................................... 14
Formation of depth and shallow lake sediments ................................................... 15
Water uses in the Bolivian Altiplano ...................................................................... 15
Materials and methods ................................................................................................ 15
Field and laboratory methods ................................................................................ 15
5.1.1
5.1.2
5.1.3
Groundwater and surface water sampling (Papers I, II & III).................................................... 15
Soil and crop sampling (Paper IV) ................................................................................................... 16
Lake sediment sampling (Paper V)................................................................................................... 16
Analytical experiments ........................................................................................... 17
5.2.1
5.2.2
5.2.3
5.2.4
Determination of major anions......................................................................................................... 17
Determination of major cations and trace elements ..................................................................... 17
Determination of trace element in sediments ................................................................................ 17
Quality control .....................................................................................................................................17
Geochemical modeling .......................................................................................... 17
Statistical analysis .................................................................................................. 17
Mineralogical investigations .................................................................................. 18
Environmental index assessments for soils, crops and lake sediments................. 18
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5.6.1
5.6.2
5.6.3
5.6.4
5.6.5
6
Availability ratio (AR) (Paper IV) ..................................................................................................... 18
Transfer factor (TF) (Paper IV) ........................................................................................................ 18
Risk assessment code (RAC) (Paper V)........................................................................................... 18
Geoaccumulation index (Paper V) ................................................................................................... 18
Metal enrichment factor (Paper V) .................................................................................................. 18
Results ......................................................................................................................... 18
6.1
6.2
6.3
6.4
6.5
7
6.6
6.7
Groundwater and surface water hydrochemistry in Poopó Basin (PB) ................. 18
6.1.1
6.1.2
6.1.3
Groundwater hydrochemistry ........................................................................................................... 18
Surface water hydrochemistry ........................................................................................................... 19
Hydrochemical types and major ions in groundwater and surface water.................................. 20
Geochemical modeling in groundwater and surface water in the Poopó Basin .... 20
Trace elements in groundwater and surface water in the Poopó Basin ................ 21
6.3.1
6.3.2
TEs in groundwater ............................................................................................................................ 21
TEs in surface water in the Poopó Basin ........................................................................................ 22
Occurrence of arsenic in groundwater in the Poopó Basin ................................... 22
6.4.1
6.4.2
6.4.3
6.4.4
Arsenic in groundwater of Poopó Basin ......................................................................................... 22
Arsenic in groundwater in Antequera and Poopó Sub-basin ...................................................... 23
As in surface water in the Antequera and Poopó Sub-basin ....................................................... 23
Distribution of major redox sensitive species (Fe and Mn) in groundwater ............................ 24
Trace element concentrations in soils (Paper IV).................................................. 25
6.5.1
6.5.2
6.5.3
6.5.4
6.5.5
Mineralogy and soil characteristics ................................................................................................... 25
Soil type of studied region ................................................................................................................. 25
Extraction of major trace element in soils ...................................................................................... 26
Available trace elements extractions in soils ................................................................................... 26
Sequential extraction of arsenic in soil ............................................................................................ 26
Trace element concentrations in crops .................................................................. 28
Trace element concentrations in lake sediments (Paper V) .................................. 28
Discussion ................................................................................................................... 28
7.1
Mechanisms controlling the hydrochemistry in the Poopó Basin (PB) (Paper I) . 29
7.2 Distinguishing hydrochemistry mechanisms in the Antequera and Poopó Subbasins (Paper II) ............................................................................................................... 30
7.2.1
7.2.2
Discrimination between processes related to groundwater chemistry....................................... 30
Describing the processes in surface water chemistry .................................................................... 33
7.3 Mobilization of trace elements and As in the hydrologic system…………………..34
7.3.1
Mobilization of trace elements and As in the groundwater environment in the Poopó Basin
(PB) (Paper I) .........................................................................................................................................................34
7.3.2
Mobilization of trace elements and As in groundwater in the Antequera and Poopó Subbasins (Paper III) ...................................................................................................................................................35
7.3.3
Mobilization of trace elements and As in surface water (Paper III) .......................................... 37
7.4
7.5
7.6
8
9
10
Mobilization of trace elements and As in transect soils (Paper IV)....................... 37
7.4.1
7.4.2
7.4.3
7.4.4
7.4.5
Mineralogical description of soils ..................................................................................................... 37
Characteristics of trace elements in soils: trends with aqua regia extractions........................... 39
Characteristics of trace elements in soil: trends with DTPA - single extraction ...................... 39
Characteristics of arsenic in soils: trends with sequential extractions ........................................ 39
Mobilization of trace elements in lake sediments .......................................................................... 39
Arsenic and other trace elements in crops ............................................................. 41
Environmental index assessment........................................................................... 42
7.6.1
7.6.2
7.6.3
7.6.4
The relationship between As and TEs in water (Papers I, II &III) ........................................... 42
Index with respect to TEs in soils and crops (Paper IV) ............................................................. 43
The relationship between TEs in soil and crops: assessment of transfer factor (Paper IV) .. 44
Sequestration and mobility of TEs in lake sediments ................................................................... 44
Conclusions ................................................................................................................. 45
Future work ................................................................................................................. 46
References ................................................................................................................... 47
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ABSTRACT
The occurrence of As in groundwater in Argentina was known since 1917; however, the occurrence, distribution and mobilization of As and other trace elements
(TEs) in groundwater in the Bolivian Altiplano are still quite unknown. An investigation applying a geochemical approach was conducted in the Poopó Basin and
Lake Titicaca to understand processes of TEs in different systems such as water,
soils, crops and sediments in mining areas.
In Poopó Basin,As, Cd and Mn concentrations exceed World Health Organization (WHO) guidelines and Bolivian regulations for drinking water in different
places around the basin, but Cu, Ni, Pb and Zn do not
In soils, the sequential extraction methods extracted up to 12% (fractions 1 and
2), which represent < 3.1 mg/kg of the total As content, as potentially mobilized
fractions, that could be transferred to crops and/or dissolved in hydrologic system. The large pool of As can be attached due to amorphous and crystalline Fe
oxide surfaces (fractions 3, 4, and 5) present in the soils.
Furthermore, the concentrations of As, Cd and Pb in the edible part of the crops
revealed that the concentrations of As and Cd do not exceed the international
regulation (FAO, WHO, EC, Chilean) (0.50 mg/kgfw for As and 0.10 mg/kgfw for
Cd), while Pb exceeds the international regulations for beans and potatoes (for
beans 0.20 mg/kgfw and for potato 0.10 mg/kgfw).
In the Lake Titicaca, principal component analysis (PCA) of TEs in sediments
suggests that the Co-Ni-Cd association can be attributed to natural sources such
as rock mineralization, while Cu-Fe-Mn come from effluents and mining activities, whereas Pb-Zn are mainly related to mining activities. The Risk Assessment
Code (RAC) indicate “moderately to high risk” for mobilization of Cd, Co, Mn,
Ni, Pb and Zn, while Cu and Fe indicate “low to moderate risk” for remobilization in the water column.
Keywords: Arsenic; Bolivian Altiplano; Eastern Cordillera; Trace elements; Surface water and shallow groundwater; Soils and crops.
the time of the Spanish conquest, when Au
and Ag were the precious metals exploited in
Oruro, Potosi and Cochabamba Departments from the 16th century until the late
18th century. Since the discovery of the most
famous mine Cerro Rico in Potosi during
1554, Bolivia was considered the major Ag
producer in the world (1554-1825), until the
crisis due to the economic recession and war
of Bolivian independence (Diaz, 2013a); and
c) post colonial period in the Bolivian Republic, with the extraction of Sb, Bi, Pb, Ag,
Sn, W and Zn, making Bolivia as the most
important global exporter of Sn throughout
the 20th century. At the beginning of 1952
the Bolivian government created the Cor-
1 I NTRODUCTION
The Bolivian Altiplano is an area with intense human activity since the discovery of
mineral resources in the colonial era. At present, it has a population of 3.451.349 (~40%
of the Bolivian population) included in the
La Paz, Oruro and Potosi Departments.
Explotation of mineral resources is the principal activity since the colonial era, and has a
major share in the economic development of
Bolivia for more than 400 years (USGS &
GEOBOL, 1992). Mining activities in Bolivia have three breakthrough periods: a) the
pre-colonial era, when Au, Ag, Cu, Hg, Pb,
and Fe were extracted (Tapia, 2011); b) at
1
poración Minera de Bolivia (COMIBOL)
with the objective of creating massive employment for miners, but the prices of minerals began their long and irreversible decline, and in 1985-1987 the prices fell to
their lowest point and production was reduced to almost zero (Tapia, 2011; Diaz,
2013b). Throughout its long history, most of
Bolivia´s mineral production has come from
a particular group of ore deposits (USGS &
GEOBOL, 1992). Currently, Bolivia is
ranked as the third largest producer of Sb,
fourth in Sn and Zn in the world (Tapia,
2011).
Private investments have increased in the Bolivian Altiplano based on the strategy of new
leasing or joint ventures between international companies (through their subsidiaries
with native names Sinchi Wayra, Manquiri
and San Cristobal) and COMIBOL. The
three companies together account for more
than half of the national production and
export of minerals (70%), cooperative companies constitute 21%, whereas COMIBOL,
which brings together state enterprises accounts for 9% of exports in recent years
never exceeding the 10% barrier (El Diario,
2012; MMM, 2013). The Bolivian mining
company Sinchi Wayra, a subsidiary of Switzerland's Glencore, operates five mines in
the Oruro and Potosi regions, Colquiri and
Porco under leasing contract, and Bolivar
under a joint venture contract with
COMIBOL, mainly exploiting Sn, Ag, Pb
and Zn. According to their production statistic, Zn, Pb, and Sn is concentrated to
205.000 Mton, 15.000 Mton and 6.000 Mton
respectively. Meanwhile, the Manquiri Mining Company a subsidiary of the Couer
d'Alene Mines Corporation is developing the
"San Bartolomé" in Potosi, with plans to
invest US$ 220 million. San Bartolomé is
oriented to the production of silver bullion
in metallurgical processing of surface materials that are deposited on the slopes and periphery of the Cerro Rico de Potosí. Finally,
the San Cristobal mine dependent on Sumitomo Corporation, is the biggest mine in
Bolivia and producing concentrates of ZnAg and Pb-Ag. It is an open pit operation
using the latest equipment and machinery,
using the floating cone method (El Diario,
2012).
High price of minerals in the current international market has increased the production, royalties and related activities in the
mining areas in Bolivia (La Patria, 2010a).
The government has increased the national
funding and prioritized new companies in
the mining areas (La Patria, 2010a, b). The
Figure 1. Map of mining activities management by COMIBOL in the Bolivian Altiplano.
Whites circles principal cities; solids squares, projects implemented 2006-2010; blues circles,
mines belong to COMIBOL; red lines, principal roads.
2
2 R ESEARCH O BJECTIVES
minerals export had increased from US$ 429
million in 2002 to US$ 3398 million in 2011
(MMM, 2012) and, as explained above, the
mining industry is the main activity in Oruro
and Bolivia.
However, the previous and current mining
activities by private, cooperatives and national companies have produced several
detrimental effects such as social disarticulation, social conflicts (CIDSE, 2009; Perales,
2010), and environmental contamination
(generation of acid rock drainage (ARD) and
acid mine drainage (AMD)). Power imbalance between the transnational companies
and the settlements and the indigenous people has lead to conflicts (CIDSE, 2009; Perales, 2010) which have been caused the loss
of the quality of their environment.
The main objective was to improve the understanding of trace elements (TEs) behavior in mining areas in the Bolivian Altiplano
and how geochemical processes govern their
behavior in the interaction between surface
water, groundwater (shallow aquifer) and
soils and content in crops and the lake sediments.
The specific objectives for this study were
to:
i) investigate the source, extent and behavior
of dissolved As and other trace elements
(TEs) in groundwater and surface water in
the Poopó Basin (Paper I), and more specifically in the Antequera and Poopó subbasins in mining areas (Paper III). Furthermore, factors and processes that lead to the
mobilization of As and TEs in groundwater
and surface water were investigated
(Paper III).
ii) make a geochemical assessment of
groundwater and surface water to evaluate
the sources of major dissolved species and
elucidate the processes that govern the evolution of natural water in the Antequera and
Poopó sub-basins (Paper II).
iii) evaluate the content of TEs in soils and
crops along three transects in relation to
different mining activities (Paper IV).
iv) evaluate the content of TEs in shallow
and deep sediments of Lake Titicaca, using
sequential extraction (Paper V).
1.1 Rationale
A large proportion of the Bolivian Altiplano
is impacted by various human activities,
which to a major extent involves mining of
the metalliferous deposits in the region, especially due to the increased mineral prices
during the last decades. Proyecto Piloto
Oruro (PPO, 1993 -1996) was the pioneering and a detailed study on the distribution
of TEs in surface waters, soils and mining
wastes in the Oruro region (PPO-03, 1996;
PPO-04, 1996; PPO-13, 1996). However,
these studies have not reported the overall
impact of TE contamination in the Lake
Poopó Basin and Lake Titicaca in the different matrices of the ecosystem such as surface- and groundwater, sediments, soil and
their crops produced due to mining activities. Thus, it was important to carry out the
present investigation which focuses on the
study of trace elements in various systems
and at different scales in the Bolivian Altiplano. The study would contribute to the
primary understanding of the distribution
and mobility of the TEs in the Bolivian Altiplano. The government environmental regulators, stakeholder, mining industry and environmental regulators can use this acquired
knowledge in the mining areas to look for
environmental solutions.
3 B ACKGROUND L ITERATURE
During the last 200 years after the industrial
revolution, huge changes in the global budget of critical organic and inorganic substances and trace elements at the earth´s surface
have occurred. Soils, plants, surface water
and groundwater have been affected by trace
elements (TEs); which may inhibit biotic
activities and reduce the diversity of populations of flora and fauna in soil. The pathways for transfer TEs to human beings may
include drinking water, consuming contaminated food, and/or indirectly from consuming other products (i.e. milk) (Förstner,
1995) and in mining and arid zones especial3
3.1.1 Trace elements and arsenic in
groundwater and surface water
ly the inhalation of dust (Goix et al., 2011).
Trace elements are essential micronutrients
for living organisms, in humans and also in
plants (Kabata-Pendias & Mukherjee, 2007).
However, some of the TEs are toxic: mercury (Hg), lead (Pb), cadmium (Cd), copper
(Cu), nickel (Ni) and cobalt (Co); the first
three are particularly toxic to higher animals
and the last three are more toxic to plants
than animals and are called phytotoxic
(McBride, 1994; Kabata-Pendias & Mukherjee, 2007) at elevated levels. Potentially hazardous TEs to human health at elevated
levels include arsenic (As), antimony (Sb),
beryllium (Be), cadmium (Cd), chromium
(Cr), copper (Cu), lead (Pb), mercury (Hg),
nickel (Ni), selenium (Se), silver (Ag), thallium (Tl) and zinc (Zn) (McBride, 1994). Bioavailable fractions of these elements are variable and are controlled by specific properties of abiotic and biotic media as well as by
physical and chemical properties of a given
element (Kabata-Pendias & Mukherjee,
2007).
Trace element (TE) contamination of soil,
surface water and groundwater poses a major environmental and human health risk.
The threat that TEs exert on human and
animal health is aggravated by their longterm persistence in the environment (Shaw,
1990). Additionally, the manner in which a
TE is bound to solids influences the mobility, bioavailability and toxicity of the element
to organisms (Bacon & Davidson, 2008).
The composition of natural water is controlled by both geochemical and geobiological processes (Morel, 1983). About
99% of the world’s fresh available water is
groundwater; a basic source of domestic,
industrial, and agricultural water supplies in
many places in the world. Therefore, the
chemical composition of groundwater and
its contamination has become of great concern recently, since the anthropogenic activities exert pressure on the quality and quantity of water resources.
Arsenic concentrations in surface water and
groundwater can vary by more than four
orders of magnitude depending on the
amount of available As in the source rocks
and the local geochemical environment
(Matschullat, 2000; Smedley & Kinniburgh,
2002). The concentration of As in unpolluted fresh water typically ranges from 1 – 10
µg/L, rising to 100 – 5000 µg/L in areas of
sulfide mineralization and mining (Mandal &
Suzuki, 2002). Arsenic and TEs can adsorb
onto several surfaces, particularly iron (Fe),
aluminium (Al), manganese (Mn) oxides and
hydroxides and silicon (Si). These natural
sorbent surfaces have been recognized for
more than a 100 years and the dissolution
and formation of solid hydroxides and oxides are important in the aquatic chemistry
of many metals ions (Morel, 1983; Dzombak
& Morel, 1990). The sorption of inorganic
ions on hydrous oxides is strongly dependent on solution conditions such as pH, ionic
strength and the presence of competing ions
(Dzombak & Morel, 1990; Smedley & Kinniburgh, 2002; Smedley et al., 2002). In contrast, desorption from hydrous oxides is one
of the principal mechanisms controlling
mobility of the anionic TEs especially when
pH values in groundwater increase (Dzombak & Morel, 1990; Smedley & Kinniburgh,
2002).
Geochemical properties such as redox potential (Eh) and pH are the most important
factors controlling As speciation (Smedley &
Kinniburgh, 2002), where As and others
TEs that form oxyanions (e.g. As, Se, Sb,
Mo, V, Cr, U, Re) are sensible to mobiliza-
3.1 Trace elements and arsenic in the
environment
In general terms of TEs abundance in the
upper continental crust is as follow: Cr is the
18th element (35 mg/kg), Zn is the 21th element (52 mg/kg), Ni is the 24th element
(18.6 mg/kg), Cu is the 27th (37.4 mg/kg),
Pb is the 34th (12.5 mg/kg), and Cd is 60th
element (Wedepohl, 1995). The most extensively studied TE is arsenic, although it is the
20th most abundant element in the continental crust (Mandal & Suzuki, 2002; HudsonEdwards et al., 2004) detectable in all soils
and sediment. Additionally, As is a ubiquitous 14th in seawater and 12th in the human
body (Mandal & Suzuki, 2002).
4
tion at pH values typically found in groundwater (pH 6.5 – 8.5) under both oxidizing
and reducing conditions (Smedley & Kinniburgh, 2002). The behavior of As can be
summarized in terms of three different redox zones: i) shallow, oxidizing zone with
dissolved O2, in which Fe(III) oxide and
hydroxides are stable and As is adsorbed; ii)
intermediate, moderately reducing zone
without O2, in which Fe(III) oxide and hydroxides reach reductive dissolution and As
is released and iii) deep reducing zone,
where SO42- is reduced with formation of
H2S. Arsenic can co-precipitate in secondary
sulfides (e.g. pyrite) (Sracek et al., 2004).
Many toxic TEs occur in solution as cations
(e.g. Pb2+, Cu2+, Ni2+, Cd2+, Co2+, Zn2+)
which generally become increasingly insoluble as the pH increases (Dzombak & Morel,
1990; Smedley & Kinniburgh, 2002). The
solubility of TEs (cations) is strongly limited
by precipitation or coprecipitation at the
near-neutral pH in groundwater (Smedley &
Kinniburgh, 2002).
main factors influencing their concentrations
in the soil; also factor such as climate, organic and inorganic components of soils and
geochemical characteristics (redox potential
(Eh) and pH) are affecting the As content in
soils (Mandal & Suzuki, 2002).
In soils, As occurs mainly as inorganic species, As(V) (arsenate) and As(III) (arsenite),
the redox potential (Eh) and pH are the
main factors for As speciation, but others
such as adsorption and microbiological activity play important roles. However, inorganic As compounds can be methylated by
microorganisms, producing monomer-thylarsonic acid, dimethylarsinic acid, trimethylarsine oxide and others under oxidizing
conditions (Mandal & Suzuki, 2002; Litter et
al., 2008); some other studies suggest that
the plants are able to methlylate inorganic As
(Raab et al., 2007).
Cadmium (Cd) is classified as a chalcophile
element, which is associated geochemically
with Zn in sulfide minerals in rocks (Fuge et
al., 1993; Garret, 2004), both having very
similar electronic structures, electro-negativities and ionization energies (Fuge et al.,
1993). High mobility is attributable to the
fact that Cd2+ adsorbs rather weakly on organic matter, silicate clays, and oxides at pH
< 6. Above pH 7, Cd2+ can coprecipitate
with CaCO3 or precipitates as CdCO3 and
Cd phosphates which thereby limits its solubility (McBride, 1994).
Copper (Cu) is also classified as a chalcophile element, associated to sulfide in very
insoluble minerals such as Cu2S and CuS
(McBride, 1994; Garret, 2004), but Cu2+
occurs in soil as a colloid and in solution
almost exclusively. However, reduction of
Cu2+ to Cu+ and Cu0 is possible under reducing conditions, especially if halite or sulfide
ions are present to stabilize Cu+. In reduced
soils, the mobility of Cu is very low. Most of
the soil colloids (Mn, Al and Fe oxides, silicate clays and humus) adsorb Cu2+ strongly,
increasing with pH. Organic complexes bind
Cu2+ more strongly than any other divalent
transition metal; the solubility of these complexes is rather low limiting their bioavailability. Conversely, the mobility of soluble
3.1.2 Trace elements and arsenic in soils/
sediments
Soils are formed at the land surface by
weathering processes derived from biological, geological and hydrologic phenomena
and they show an approximately vertical
stratification produced by the continual influence of percolating water and living organisms (Sposito, 1989). The mobilization of
TEs from rocks to soils, sediments and dissolution in water is dominated by both abiotic and biotic processes (Morel, 1983). They
can be incorporated into plants and animals
and became parts of food chains (Sposito,
1989; Garret, 2004).
Arsenic occurs as a major constituent in
more than 200 different minerals, including
elemental As, arsenides, sulfites, arsenites,
arsenates and oxides (Smedley & Kinniburgh, 2002; Mandal & Suzuki, 2002). The
most important As-bearing minerals are
mixed sulfides: arsenopyrite (FeAsS); realgar
(AsS), niccolite (NiAs), cobaltite (CoAsS)
(Matschullat, 2000). The terrestrial abundance of As is around 1.5 – 3 mg/kg, where
parent rocks and human activities are the
5
3.1.3 Trace elements and arsenic in plants
complexes of Cu2+ may be significant under
high pH conditions (McBride, 1994).
Lead (Pb) is a strongly chalcophilic element,
occurring primarily as PbS in rocks and insoluble in reduced soils (McBride, 1994;
Garret, 2004). Under oxidizing conditions,
the Pb2+ ion becomes less soluble as the
soil´s pH is raised. Complexes with organic
matter, chemisorption on oxides and silicate
clays, and precipitation as the carbonate,
hydroxide, or phosphate are all favored at
higher pH. In alkaline soils, solubility may
increase by formation of soluble Pb-organic
and Pb-hydroxy complexes. The ion Pb2+
has a particularly high affinity to Mn oxides,
this fact perhaps explained by Mn oxidation
of Pb2+ to Pb4+, a very insoluble ion. Lead is
the least mobile TE in soils, especially under
reducing or non-acid conditions (McBride,
1994).
The divalent nickel (Ni2+) is the only stable
form of nickel (Ni) in soil environment. The
ion Ni2+ is almost as electronegative as Cu2+.
This fact and its electronic structure favor
the formation of complexes with organic
matter that are comparable in stability to
those of Cu2+. As the smallest of the divalent
ions Ni2+ fits easily into octahedral sites, coprecipitating readily into Mn and Fe oxides
in soils. Chemisorption on oxides, noncrystalline alumino-silicates, and layers silicate
are favorable above pH 6, but lower pH
favors exchangeable and soluble Ni2+
(McBride, 1994).
Zinc (Zn) in soils tends to occur as a sulfide
mineral (a chalcophile mineral, sphalerite
ZnS) in rocks. In acid aerobic soils, Zn has
moderate mobility, and is held in exchangeable forms on clays and organic matter. At
higher pH, however, chemisorption on oxides and alumino-silicates and complexes
with humus decrease the solubility of Zn2+.
Consequently, Zn2+ mobility in neutral and
slightly alkaline soils is from very to extremely low, while Zn-organic complexes
can become soluble and raise mobility. In
strongly alkaline soils, Zn-hydroxy anions
may form to increase the solubility
(McBride, 1994).
Trace element concentrations in plants reflect, in most cases their abundance in
growth media (soil, nutrient solution, water)
and in ambient air. Metabolic fate and role
of each element in plants can be characterized in relation to the basic processes such
as: i) uptake (absorption), ii) transport within
plants, concentration, and speciation, iii)
metabolic processes, iv) deficiency and toxicity, and v) ionic competition and interaction (Kabata-Pendias & Mukherjee, 2007).
Trace elements such as Cu, Fe, Mn, Mo, and
Zn play a key role in plant metabolisms and
are constituents of several enzymes. However, different plants exhibit various tendencies
in uptake of TEs, depending on several factors, both internal and external. Also, plants
exhibit a variable, and sometimes specific,
ability to absorb TEs from soil and by
above-ground parts from atmospheric deposition (Kabata-Pendias & Mukherjee, 2007).
The toxicity of Ni to plants occurs in acid
soils formed from serpentinite or other ultrabasic rocks. High organic matter levels in
Ni-rich soils can solubilize Ni2+ as organic
complexes, at least at higher pH. Nickel is a
strongly phytotoxic element, being several
times more toxic than Cu (McBride, 1994).
Most of Pb in soils appears to be unavailable
to above ground parts of plants, but plants
can absorb Pb2+ and concentrate it in their
roots, carrying very little from roots to
above ground parts as long as the plants are
actively growing. Toxic effects of Pb on
plants have not often been observed, but a
hazard to animal exists because of the inherently higher toxicity of this element to animals (McBride, 1994).
Toxicity of Zn to plants is most likely to
appear in acid soils that have not been subjected to prolonged acid leaching. The rather
high potential solubility of Zn2+ in acid soils
and the fact that Zn2+ is typically a high concentration pollutant of industrial wastes and
sewage sludge, both combine to create a
significant potential for phytotoxicity from
adding wastes of soil (McBride, 1994).
Arsenic accumulation in a plant depends on
the amount available in soils. However, it
can be sorbed on clay and complexed by
6
organic matter which thereby decreases its
bioavailability. Organic acids and root exudate can increase the amount of available As
and exert an action on sites where the As is
adsorbed. Arsenite shows a high toxicity to
humans compared to arsenate and organic
species like arsenobetaine which is less toxic
(Bergqvist et al., 2014). In a recent study,
Zheng et al. (2011) showed that the root
hairs of barley play an important role in the
transfer of Cd from soils. In addition, several studies have reported that Cd translocation from roots to shoots is driven by transpiration (Zheng et al., 2011).
The TE ingestion in food is the one of the
main pathways for accumulating them inside
the human bodies over time. Food contaminated with Cd can cause bone fracture, kidney dysfunction, hypertension, and even
cancer (Nordberg et al., 2002; Turkdogan et
al., 2003). Mn and Cu can cause mental diseases such as Alzheimer and manganism in
high concentrations (Dieter et al., 2005). Ni
ingestion can cause dizziness, fatigue, headache, heart problem, fatal cardiac arrest, and
respiratory illness (Muhammad et al., 2011).
Excessive Zn can cause a sideroblastic anemia; while, Zn deficiency can cause anorexia,
diarrhea, dermatitis, depression immune
dysfunction, poor wound healing and a impared immune response. Therefore, an adequate amount of Zn is very important for
normal body functions (Khan et al., 2013).
In a recent review, Bundschuh et al. (2012)
discussed the presence of As in the food
chain across Latin America. Among the
countries in Latin America, in Mexico (Prieto-García et al., 2005), Argentina (PerezCarrera et al., 2009) and Chile (Sancha &
Marchetti, 2009) have significant levels of
TEs and As has been reported in food (Díaz
et al., 2004; Muñoz et al., 2002). Queirolo et
al. (2000) reported high As, Cd and Pb contents in vegetables in Andean villages of
northern Chile. In other areas of Chile studies showed that the levels of total As in vegetables were below the permissible limit of
the Chilean legislation (Muñoz et al., 2002).
Recently, Rötting et al. (2013) have studied
the As and Pb contents in soils and crops
near the smelter of the Vinto Metallurgical
Company (VCM) in Oruro. Their results
suggested that all crops cultivated around
VCM largely exceed As and Pb guidelines
for crop consumption.
3.2 Trace elements and arsenic in
Latin America and Bolivia from
natural
and
anthropogenic
sources
3.2.1 Argentina
In the beginning of the 20th century (1917),
Argentina was the first country to report the
presence of As in hydrologic systems in the
Chaco Pampean plain (Bundschuh et al.,
2012). Arsenic and TE studies have increased in several ecosystems and the occurrence of them has become a great concern;
actually, there are several studies in terms of
TEs in different ecosystems:
Natural sources
A thorough review of As and other TEs in
groundwater was performed by Nicolli et al.
(2012a). They summarized the sources and
explained the dissolution, and the desorption
processes in the Chaco-Pampean plain
(Smedley et al., 2005; Bhattacharya et al.,
2006b; Bundschuh et al., 2012; Nicolli et al.,
2010; Nicolli et al., 2012a, b; Rosso et al.,
2011; O`Reilly et al., 2010). Also, As speciation in surface water (rivers and lakes) and
thermal springs sites (Farnfield et al., 2012)
and TEs in the food chain (Revenga et al.,
2012) and As in milk (Pérez-Carrera & Fernández-Cirelli, 2005) have been studied.
Anthropogenic sources
Bermudez et al. (2012) found that the fluxes
of As, Cu, Pb and Zn in atmospheric deposition in Cordoba were higher than in other
agro-ecosystems.
3.2.2 Bolivia
Natural sources
In the Bolivian Altiplano, Dejoux and Iltis
(1992) conducted a review on Lake Titicaca,
this review was about formation and geological evolution (Lavenu, 1992), hydrochemistry of the lake and inflow rivers (Carmouze
et al., 1992), climatology and hydrology
(Roche et al., 1992) and limnology evaluation; making a whole analysis of biotic and
abiotic processes that occur in Lake Titicaca.
7
In the beginning of the 21st century in the La
Plata Basin (south of Bolivia), studies on
TEs were carried out in mining-affected
areas. Smolders et al. (2004), reported that
the water chemistry of the Pilcomayo River
was highly variable during the year and the
possible effect on biota, especially regarding
metal speciation and metal toxicity was discussed briefly. Miller et al. (2004) examined
four communities along the Pilcomayo River, and found that the most significantly
contaminated soils occurred with Cd, Pb,
and Zn, these concentrations exceeded recommended guideline values for agricultural
use. However, the results suggested that
most vegetables do not accumulate significant quantities of TEs. Hence, the most
significant exposure pathway appears to be
the ingestion of contaminated soil particles
attached to and consumed with vegetables.
Archer et al. (2005) concluded that mining
should not be held solely responsible for As
contamination of drinking water in the Pilcomayo basin, there is also a natural weathering of bedrocks. Kossoff et al. (2011,
2012a, 2012b) found that a high degree of
the metal mobility was recorded in the tailing dam in spill-simulated column experiments, stressing the potentially serious
short-to-long-term effects that accompany
tailing dam spill into floodplain environment. Also, they demonstrated the effect of
mine tailing on the load and cycling of As, P,
Pb and Sb in foodplain soils and showed
that their natural weathering and oxidation
can lead to formation of relatively insoluble
As, Pb and Sb-bearing phases that have wide
pH – Eh stability fields.
In the southern part of the Bolivian Altiplano, studies at Poopó Basin had focused
on assessment of TEs in surface water, soil
and mine waste material, the Proyecto Piloto
Oruro (PPO–03,1996; PPO–04, 1996;
PPO–13, 1996) was the pioneer study in the
Oruro mining areas; others studies were
made to understand the geochemical processes in groundwater and surface water
(Banks et al., 2002; Lilja & Linde, 2006;
Quino, 2006) and in lake sediments (Cáceres
Choque et al., 2004, 2013; Selander & Svan,
2007; Tapia & Audry, 2013). Recently, Goix
et al. (2011) carried out a study of the
transport of atmospheric aerosols and found
high TE concentrations, some of them higher than values reported in the literature, confirming that the smelters are one of the
sources and another probably the resuspension of soil dust by ore deposit transportation. Rötting et al. (2013) studied the As and
Pb contents in soils and crops near the smelter of the Vinto Metallurgical Company
(VCM) in Oruro, their results suggesting that
any crops cultivated around VCM should
not be consumed due to the high As and Pb
contents in the crop.
3.2.3 Brazil
Natural sources
TE contents in fish and seafood were evaluated (Medeiros et al., 2012; Morgano et al.,
2011), as well as in rice (Batista et al., 2010).
In addition, Scarpelli (2005) evaluated As in
rivers of the Amazon Basin, from the Andes
Cordillera to the Atlantic ocean. A thorough
study of As in different ecosystems and humans in Iron Quadrangle was performed by
Deschamps and Matschullat (2007).
Studies on TEs were focused on As, Ono et
al. (2012) found that the total As concentration in soils was high in mining areas, however, bioavailable As was low (< 4.2%), indicating a low risk from exposure of children
next to this area. Amount of As and TEs in
surface water and sediments in the Iron
Quadrangle study were assessed using a sequential extraction procedure to evaluate
mobility of As and TEs (Varejao et al.,
2011).
3.2.4 Chile
Natural sources
Díaz et al. (2004) studied the contribution of
water, bread and vegetables to the dietary
intake of As in a rural village in northern
Chile. Also, Muñoz et al. (2005) studied the
dietary intake of As by the population in the
nation´s capital Santiago, it was estimated as
being 77 µg/day using a total diet study.
8
Figure 2. a) Eastern and Western Cordillera, b) Poopó Basin, and c) Antequera and Poopó
sub-basins and (T1, T2, and T3) transects scale. Location of sampling places surface water,
groundwater, soil, and crops. Political borders, orange colored Poopó; pink colored, Antequera and magenta colored, Pazña municipalities.
9
Neaman et al. (2012) found that application
of earthworms in Cu and As contaminated
soils improves the quality of soil. Molina et
al. (2009) studied contribution of fertilizers
in term of TEs and found that long-term use
of P fertilizer may increase levels of As, Cd
and other TEs in agricultural soils.
4 S TUDY A REA
4.1 Study site description
Three different units are discussed i.e. basin,
sub-basin and transect: i) Titicaca and Poopó
Basins are considered in the northern and
southern areas of the Bolivian Altiplano
(BA), ii) second, Antequera and Poopó Subbasins, whose rivers drain their waters into
Lake Poopó, which is part of the Poopó
Basin (PB), and finally iii) transects located
in the Poopó municipality. In order to avoid
misunderstanding with the names in the
following each transect will be called T1 for
Coriviri, T2 for Ventaimedia and T3 for
Poopó transects (Fig. 2).
4.1.1 Poopó Basin (PB) – (Paper I)
The Poopó Basin (PB) covers an area of
about 25.000 km2 which is integrated by the
Lakes Poopó and Uru Uru, from a morphologic perspective the basin can be divided
into three regions: i) eastern mountain region, occupying ~40% of total area (3800 –
5000 m a.s.l.; above sea level); ii) western
mountain region, occupying only a small
part of the basin (3800 – 4800 m a.s.l.) and
finally iii) Inter-Andean flat, constituting half
of basin (3700 – 3800 m a.s.l.) (Pillco &
Bengtsson, 2006). The PB includes 22
ephemeral inflow rivers, the biggest are the
Marquez, Sevaruyo, Desaguadero and Antequera Rivers (Pillco & Bengtsson, 2006).
The Poopó Basin has been divided into five
regions (R-I – R-V) to better understand the
diverse environmental aspects (Fig. 2)
(PAADO, 2005).
4.1.2 Antequera and Poopó Sub-basins –
(Papers II and III)
The Poopó and Antequera Sub-basins are
located in the Poopó Province of the Oruro
Department; they are located at 18°14’36”
and 18°33’54” latitude south and 67°04’14”
and 66°45’50” longitude west, respectively.
The sub-basins (Antequera and Poopó) are
situated on the eastern shore of Poopó Lake,
and the rivers with same names discharge
their waters into the Lake Poopó, and comprise an area of 226.3 km2 and 109 km2, respectively (Fig. 2).
4.1.3 Transects Coriviri, Ventaimedia, and
Poopó – (Paper IV)
Transects T1, T2 and T3 are located on the
eastern side of Lake Poopó and are affected
by mining activities in the trends of Eastern
Cordillera. Soils and crops were collected in
Figure 3. Communication between Northern and Central Altiplano (Modified from Fornari et al., 2001; Tapia, 2011); b) location of the sediments sampling point in Lake
Titicaca.
10
three transects taking into account different
topographical settings. The sites were selected following criteria such as representativity,
productivity, crop diversity, crop consumption as described in Paper IV (Fig. 2).
4.1.4 Titicaca Basin – (Paper V)
Lake Titicaca is located in the Andes Cordillera at an elevation of 3812 m a.s.l., on the
border between Bolivia (45%) and Peru
(55%). Its maximum depth is 281 m (average
depth 107 m). It consists of two bodies of
water separated by the strait (i.e. Tiquina
Strait); the larger body to the northern side is
known as the Major Lake or Chucuito (area
6450 km2), reaching in this part its greatest
depth near the Soto Island. Minor Lake or
Huiñaymarca located toward the south covers an area of 2112 km2, with a maximum
depth of 45 m (Boulange & Aquize, 1981)
(Fig. 2).
4.2 Paleolakes development in northern and central Bolivian Altiplano
The Altiplano is a vast endorheic basin in
central Andes of Peru, Bolivia and Argentina
located between the Eastern and Western
Cordilleras (200.000 km2). Since the early
Quaternary period, the Altiplano has always
been occupied by lakes, but these have not
always had the same size as the present day
lakes. Studies of these ancient lakes and the
main glacial stages in the Eastern Cordillera
have allowed the establishment of relationships between three lake formations and
three most recent stages of glacial recession,
Lake Ballivian in the northern basin and
Escara, Minchin (30 – 25 ka BP; before present) and Tauca (12 – 10 ka BP) in the
southern basin (Risacher & Fritz, 1991; Lavenu, 1992; PPO-03, 1996; Tapia et al., 2003)
(Fig. 3).
These lake systems in the Bolivian Altiplano
is the result of evolution of a more ancient
system which began from lower Pleistocene,
with transition at the end of Pliocene from a
relatively warm climate to a cool damp climate. The presence and the size of the lakes
are directly related to the recession of glaciers at the start of interglacial periods
(Lavenu, 1992; Tapia et al., 2003; Rigsby et
al., 2005).
The modern Desaguadero River (flow 390
km) drains from Lake Titicaca (elevation
3810 m a.s.l.; in relatively wet northern Altiplano) to shallow Lake Poopó (3685 m
a.s.l.); in drier central Altiplano). Accordingly the interannual changes in the level of
Lake Titicaca has a dramatic influence on
discharge of Desaguadero River. The latter is
also enhanced by more local runoff, especially that of the Mauri River (mean flow 21
m3/s in the period 1977 – 2001) (Rigsby et
al., 2005; Pillco & Bengtsson, 2006).
4.3 Geological settings
The Altiplano is located between the metasedimentary Eastern Cordillera and the volcanic Western Cordillera of the Andes
(USGS & GEOBOL, 1992). The Eastern
Cordillera system runs from north to south
and northwest to southeast, reaching altitudes up to 5000 m a.s.l. and is composed of
intensely folded and faulted marine sandstones and shale of the Paleozoic and Mesozoic ages (YPFB & GEOBOL, 1996; SERGEOMIN, 1999). These rocks were deposited on the Precambrian basement and deformed by at least three orogenic cycles
from the Paleozoic to the Cenozoic eras.
They are composed of intensely fractured
Ordovician limestones, quartzites, slates and
schists, with low angle faulting (USGS &
GEOBOL, 1992; YPFB & GEOBOL,
1996) (Fig. 1a).
In the Bolivian Altiplano and Western Cordillera sediment deposits corresponding to
the Miocene to Pliocene ages that host redbed copper deposits and mainly epithermal
Ag-Au-Pb-Zn-Cu deposits formed during
the Middle-Late Miocene and Early Pliocene
(USGS-GEOBOL, 1992; Redwood 1993).
The Bolivian Sn, Au-Sb and Pb-Zn belts are
hosted in the Oruro Department and in the
Eastern Cordillera (Arce-Burgoa & Goldfab,
2009). The Bolivian Sn belt continues for
900 km east-west throughout Bolivia from
northernmost Argentina to southernmost
Peru (Arce-Burgoa & Goldfab, 2009; Tapia
et al., 2012)
4.3.1 Geology around the Titicaca region
Lake Titicaca (Lakes Major and Minor) is
located in the north part of the endorheic
11
Figure 4. Rain distribution in the Poopó Basin. (Source: Pillco & Bengtsson, 2006).
basin which formed during the Pliocene and
Early Pleistocene (around 3 – 2 Ma). The
latter period was marked by periodic advances and retreats of glaciers, and these
result in high-amplitude fluctuations of lacustrine basins (Lavenu et al., 1984; Servant
& Fontes, 1978; Mourguiart et al., 1992;
2000). Lake Titicaca is characterized by receiving drains from four different geological
formations: Volcanic, Devonian, Carboniferous and Cretaceous and lacustrine sedimentation, which are characterized by six
different facies: detrital, carbonate detrital,
carbonate, organo-detrital, carbonate organo-detrital, and organic facies (Rodrigo &
Wirrmann, 1992).
4.3.2 Oruro mineral deposits
Mineral resources are deposited in the Eastern Cordillera which includes the wellknown Bolivian Sn belt, Au-Sb, and Pb-Zn
belts (Tapia et al., 2013), that occur in the
study area of the Coriviri, Poopó, Candelaria
y Bolivar-Avicaya districts. The PoopóCandelaria polymetallic belt is situated at the
boarder of the Uyuni-Uyuni fault. West of
the fault large sedimentary deposits of gravel, sand and silt are to be found and east of
the fault the Eastern Cordillera’s Palaeozoic
block is situated with its siltstone, quartzite
and slate composition (PPO-04, 1996).
The Poopó and Avicaya–Bolivar districts
consist mainly of Silurian sediments; they
contain quartzite and slate in the Llallagua
Formation and lutites in the Uncia Formation with more than 2 km thickness in
this area. The main veins are Bolivar, Nane,
Pomamba; those form systems of 1 km
length (PPO-04, 1996). These zones have
been the most exploited, even to date, due
to their high content of Sn and Ag compounds of easy benefit (GEOBOL, 1992).
The Poopó-Candelaria Zn, Ag-Sn belts, correspond to Bolivian polymetallic vein type
deposits, associated with small sub-volcanic
felsic intrusions, and zoned hydrothermal
alterations around igneous bodies with various Sn deposits to the northeast, east and
southeast of Poopó (Monserrat, Challa
Apacheta & others) (GEOBOL, 1992).
4.4 Climate around the Bolivian
Altiplano
The Andes Cordillera, running continuously
from north of the equator to the southern
tip of South America, represents a formidable obstacle to tropospheric circulation and
acts as a climate barrier. Along its central
portion (15oS – 22oS), widening of the Andes
produces distinctive meteorological conditions called the climate of the Altiplano. The
interest in the climate of the Altiplano has
grown as its variability has a strong impact
on availability of water resources in this
semi-arid region and adjacent lowlands
(Garreaud et al., 2003).
The Altiplano rainfall is largely restricted to
the austral summer season (November to
March) especially along its southwestern
part, where more than 70% of the precipitation occurs from December to February
(Garreaud et al., 2003). The climate is classified as semiarid for the northern and middle
parts, while the southwestern part is arid
12
(TDPS, 1993). Moisture availability in tropical lowlands is thus not a dominant regulating factor for Altiplano precipitation; while
the significant El Niño Southern Oscillation
(ENSO) related cooling or warming of the
tropical troposphere also leads to a direct
relationship between ENSO phases and
near-surface temperature fluctuations over
the Altiplano (Garreaud et al., 2003). Moisture from the Amazonian basin is advected
into the central Andes. Warm saturated air
condenses at higher altitude, producing rainfall on the eastern slope of the Andes and on
the Altiplano (Tapia et al., 2003).
potential annual and monthly evapotranspiration are 1241 mm and 103 mm, respectively, for the period 1990 – 2010 (Zapata,
2011).
The mean annual average temperatures of
the Altiplano are between 7oC and 10oC
(Roche et al., 1992). The mean potential
evaporation rate over the entire Altiplano is
estimated at more than 1500 mm/year
(Roche et al., 1992) and varies from 1500 to
1800 mm/year in the north-south direction
(TDPS, 1993). However, pan observations
and Penman equation correction have estimated the potential evaporation close to
1700 mm/year in Lake Poopó (Pillco &
Bengtsson, 2006).
Rivers flowing to the lake can be divided
into three groups with distinctive drainage
basin lithologies. The first group is comprised by the Suches, Huaycho and Keka
Rivers, which drain from the Eastern Cordillera. Their drainage basins are composed
mostly of Silurian-Devonian continental
sedimentary rocks, Permian marine sediments and minor Tertiary lavas and intrusive
rocks. The second group includes the Coata,
Ilave and Ilpa Rivers, which drain the Western Cordillera with Plioceno-Quaternary
volcanic and ignimbrite formations, in addition to lavas, ignimbrites and associated volcanogenic sediments, lesser amounts of
Jurasic and Cretaceous marine sediments
and Tertiary continental sediments. The
third group consists of rivers with drainage
basins north of Lake Titicaca (Lake Major)
and their drainage basins include Cretaceous
continental and marine sediments (including
limestones); Permian, Tertiary and Quaternary volcanic rocks and volcanogenic sediments; Silurian, Devonian and Ordovician
marine sediments and Carboniferous sediments; and widespread Quarternary lacustrine deposits (Carmouze et al., 1992; Roche
et al., 1992; Grove et al., 2003).
Around Lake Titicaca the temperature remains above 8oC and the presence of the
lake makes the climate more temperate decreasing the temperature range, but it does
not seem to cause an increase of the mean
annual temperature by more than 2oC
around its margins. The mean annual relative
humidity around Lake Titicaca varies between 50% and 65% (Roche et al., 1992).
The rainy season is from December to
March and is centered in January, while the
middle of the dry season (May to August) is
June; two transitional periods separate these
seasons, one in April and the other from
September to November. Rainfall over the
lakes is greater than 800 mm and can reach
1000 mm. Maximum monthly rainfall recorded over the lake reached 300 to 450 mm
in January 1984, a particularly rainy month
(Roche et al., 1992).
Available rainfall data for the Poopó Basin
show that the average annual rainfall for a 42
year period (1960 – 2003) is 372 mm (Pillco
& Bengtsson, 2006) (Fig. 4). The median
4.5 Hydrology
Altiplano
in
the
Bolivian
The main hydrologic system of the Altiplano
corresponds to Lake Titicaca (Chucuito (Major) and Huayñamarca (Minor)), it is drained
by the Desaguadero river which reaches
Lakes Uru Uru and Poopó, finally connected
to Coipasa Salar (TDPS, 1993).
4.5.1 Lake Titicaca
Higher Sr isotopic values in waters from
Lake Minor indicate a lack of complete exchange with Lake Major; additionnally, difference of distribution in Sr isotopes between the northeast and southwest areas of
Lake Minor also demonstrates limited exchange between and differing inputs to the
three sub-basins of Lake Minor (Carmouze
et al., 1992; Roche et al., 1992; Grove et al.,
13
2003). At modern lake levels, about 10% of
the annual input of water to Lake Titicaca
leaves the basin through its outlet (i.e. the
Desaguadero River).
4.5.2 Desaguadero River
Lakes Titicaca and Poopó are connected by
the Desaguadero River (390 km) and there
are several tributaries on its way to Lake
Poopó. The main tributary is the Mauri River located southwest of Lake Titicaca. The
average annual discharge in downstream
Desaguadero River at the inlet to Lake Poopó Basin is 66 m3/s in the period 1960 –
2002; the maximum and minimum annual
discharge is 279 and 16 m3/s, respectively
(Pillco & Bengtsson, 2006).
Downstream from the Lake Titicaca outlet,
flow in rivers is increased by seasonally variable discharge from tributaries that strongly
influence the hydrology and chemistry of the
Desaguadero River. Further downstream,
the river becomes increasingly diluted by
freshwater tributaries, some of which drain
Altiplano sediments and also volcanic rocks
of the Western Cordillera (e.g. the Mauri
River) (Grove et al., 2003).
4.5.3 Lake Poopó
The water is highly concentrated by evaporation in Lake Poopó and isotopically enriched
by the Machacamarca, Poopó, Pazña, Sevaruyo, Marquez and Mulato Rivers. Their water drains from Silurian-Devonian sandstones and mudstones of the Eastern Cordillera as well as Miocene ignimbrites and
dacitic lavas of the Los Frailes Cordillera
(Grove et al., 2003).
4.6 Source of salinity in shallow aquifers in Poopó Basin (PB)
4.6.1 Poopó Basin (PB) salinity in shallow
aquifers
The hydrologic changes during the late Quaternary have evidenced the existence of
paleolakes in the central Bolivian Altiplano
(BA) which is marked by high shoreline terraces and lacustrine sediments. Some early
studies found that the paleolakes were
formed by inputs of glacial melt water to the
basin, recent work has focused on increased
precipitation, decreased evaporation, or
both, to explain the formation and maintenance of these paleolakes (Grove et
al., 2003).
The previous studies on the BA to determine the origin of groundwater recharge at
different aquifers were performed in the
central BA, Coudrain-Ribstein et al. (1995a,
b). Hydrogeological modeling and interpretation of isotopic data of δ18O for rain, river
(Desaguadero) and groundwater indicate
that the latter has similar values (-15‰) to
those of summer rainstorms which recharge
the aquifer and the zone where recharge by
the river Desaguadero was expected the
groundwater δ18O are higher (-10‰). Electrical conductivity (EC) and δ18O data show
that the evaporation is not sufficient to explain the increasing salinity in the groundwater. Dissolution of salty Quaternary sediments is likely to contribute to the excess
salinity. Additionally, isotopic studies of tritium (3H) and 14C analysis indicate that the
groundwater is 4000 years old in the basin
located in the central BA (Coudrain-Ribstein
et al., 1995a, b).
Almost all rivers disappear before reaching
the alluvial fans and Lake Poopó, suggesting
that some part of their water is reaching the
aquifers during the dry period, while the
opposite happening during the rainy period,
with high runoff events which cause flooding in the alluvial fans in many places around
Lake Poopó. This observation is in agreement with both conditions of clay sediments
which represent low permeability and semiarid conditions in the eastern basin and arid
conditions in southern-western of the PB.
Additionally, the water table is located close
to the surface, which is linked to high evaporation rates, having produced extensive deposits of evaporates composed mainly of
halite (Aravena, 1995).
4.6.2 Sub-basin (Antequera and Poopó)
recharge
Zapata (2011) has reported that the isotopic
composition (δ18O and δ2H) of groundwater
and surface water in the Poopó sub-basin,
has predominantly meteoric source (compared with the Local Meteoric Water LineLMWL; δ2H= 8.3 δ18O + 16.9).
14
Also isotopic results suggest enrichment of
both isotopes δ18O and δ2H which are on
the evaporation line (δ2H= 4.7δ18O+40.8)
reported previously by Lizarazu et al. (1987)
and Fontes et al. (1979). Hence, considering
the few studies in the BA, it is possible conclude that in whole basin there are two different sources: i) the recharge of groundwater by evaporation influenced by surface
water infiltration and ii) direct meteoric recharge of the shallow aquifer. Furthermore,
it is important to assess the shallow and
deep aquifers in order to identify the water
resources for the near future in the BA.
4.7 Formation of depth and shallow lake
sediments
It is now well established that the level of
Lake Titicaca was at least 85 m below the
present day level at some time during the
early and middle Holocene and higher than
the modern level during the Last Glacial
Maximum (LGM; Baker et al., 2001). The
LGM sediments were influenced globally
which is documented by oxidized units elsewhere in the world under probably similar
conditions (McArthur et al., 2008). Around
the Bolivian Altiplano the LGM (ca. 18–20
ka) caused the absence of the ostracods,
which has been interpreted as unfavourable
conditions for calcified organisms because
the climate was much colder and the pH was
lower (Mourguiart et al., 1992; Mourguiart,
2000). This global condition in the sediments has affected the biogeochemistry
around the Altiplano.
4.8 Water uses in the Bolivian Altiplano
In the Titicaca Basin, currently, there are
many small companies concerned with fish
farming and tourism in the Lake Major
which are increasing their activities, and also
the inhabitants like fishing of native and
introduced species.
In the Poopó Basin, the evaluation of water
uses has estimated that the major consumption is for industrial (included mining) activities 0.5 – 0.6 m3/s, for irrigation 8.1 m3/s,
and for domestic use 0.2 m3/s. The mining
consumption could be underestimated due
to the lack of information in the Poopó Basin (Calizaya, 2009).
5 M ATERIALS
AND METHODS
5.1 Field and laboratory methods
5.1.1 Groundwater and surface water
sampling (Papers I, II & III)
Surface (n= 4) and groundwater (n= 28)
samples were collected around Poopó Basin,
where groundwater samples were taken
from excavated wells (< 25 m depth) in
small towns and one drilling well (< 80 m
depth, Paper I). The water samples were
collected in the dry season (September 2007;
Paper I). Another set of surface (n= 22) and
groundwater (n= 30) samples were collected
in February 2009 in the rainy season in the
Antequera and Poopó Sub-basin (Papers II
& III); most of the surface water was located
in the headwater region (headwaters: i.e.
before flowing through areas with mining
activities or the whole sub-basin).
A Nansen bottle (plastic material) was used
to take groundwater samples according to a
procedure describing by standard sampling
methods (Bhattacharya et al., 2006a, b). The
sample bottles were rinsed three times with
water at each sampling site. Samples were
collected and filtered through 0.45 µm filters
using a hand filtration unit; they were divided in three lots:
Type 1: 100 mL for major anion analysis; for
chloride (Cl-); nitrate (NO3-); sulfate (SO42-).
Type 2: 100 mL for major cation analysis:
sodium (Na+); potassium (K+); calcium
(Ca2+); and magnesium (Mg2+).
Type 3: 100 mL for TEs and phosphate
(PO43-); filtered samples acidified with
HNO3 (pH< 2) (aluminum (Al); arsenic
(As); cadmium (Cd); copper (Cu); lead (Pb);
iron (Fe); manganese (Mn); silicon (Si); zinc
(Zn)). All samples were stored at low temperature (4oC) until further analyses in lab.
Multiparameter equipment was calibrated
using standard solutions for pH, electrical
conductivity (EC), redox potential (Eh) and
total dissolved solid (TDS) in the field and
15
measurements were performed as described
in Papers I, II and III.
residual phases, the method is described in
detail in Paper IV.
Alkalinity was also determined in the field by
titration with 0.01 M HCl until the endpoint
(at pH 4), as indicated by a color change of a
mixed acid-base indicator (indigo carmine
and methyl orange; Merck proanalysis reagent) (Papers I, II & III).
The TE concentration associated to a specific extractant was expressed as follows: [i]j
where i is the TE and j relates to extractant
(i.e., [i]regia for HNO3/HCl, [i]DTPA for DTPA
and [i]stp1-stp5 for sequential extraction procedure in the step 1 – 5).
5.1.2 Soil and crop sampling (Paper IV)
Crop sampling (Paper IV)
Crops (alfalfa (Medicoga sativa), barley (Hordeum vulgare), beans (Vicia faba) and potatoes
(Solanum tuberosus)) were collected during the
period of harvesting jointly with the soils at
the sample sites. Along each transect the
same four crops were sampled in order to
make a comparison between the places. Edible part of the crops were selected and dried
at ambient temperature for a day followed
by subsequent oven drying at 70 – 80oC for
24 h to remove moisture (Paper IV).
Soils sampling (Paper IV)
Top soils were collected (~2 kg) up to a
depth of 0.30 m and homogenized in the
field as composite samples. Samples were
dried at ambient temperature and sieved
through a 2 mm mesh prior to analysis in
lab. Physical and chemical properties were
measured in field and in lab, variables include: depth, slope, soil water content, soil
pH, texture, electrical conductivity (EC), and
standard methods were used to determine
the cations (Na+, K+, Ca2+, Mg2+), organic
matter (OM) (Walkley, 1946; Jackson, 1958),
cation exchange capacity (CEC), available
phosphorus (P), and clay content.
For the pseudo total digestion (i.e. As, Cd,
Cu, Pb and Zn), the soil samples were digested in a microwave closed system (3000
Anton Paar) with aqua regia (1:3 mixture of
HNO3 and HCl, both purified by subboiling distillation). The residues represent
the presence of SiO2 and were separated by
filtration through Whatman filter paper; the
procedure is explained in detail in Paper IV.
Furthermore, in order to evaluate the bioavailable contents of TEs (i.e. As, Cd, Cu, Pb
and Zn) in agricultural soils, the soil samples
were extracted with diethylenetriaminepentaacetic acid (DPTA) (mixture of
DPTA, CaCl2, and TEA (HOCH2CH2)3N) in
order to recognize potential bioavailable
TEs (ASA, 1982; Paper IV).
For a detailed evaluation of As in the soils a
sequential extraction procedure (Wenzel et
al., 2001) was applied to obtain the following
fractions: non-specifically sorbed, specifically
sorbed, amorphous and poorly-crystalline
hydrous oxides of Fe and Al, wellcrystallized hydrous oxides of Fe and Al and
A mixture of ultra-pure H2O2 (30% v/v),
HNO3 (65% m/v) and HCl (37% m/v) was
used to digest the samples. Pseudo total contents of TEs (i.e. As, Cd, and Pb) were assessed, the procedure is explained in detail in
Paper IV.
5.1.3 Lake sediment sampling (Paper V)
The samples were taken from 8 – 156 m
depth in the Lakes Minor (Huañaymarca)
and Major (Chucuito) (Lake Titicaca). They
were collected using a stainless steel grab
sampler and stored in closed plastic vessels,
and dried at room temperature. The samples
were ground and passed through a 270 mesh
sieve (<53 µm); finally, they were homogenized and stored in polyethylene plastic bags
(Paper V).
The dry samples (200 mg) were transferred
quantitatively to a quartz vessel and digested
with aqua regia (HNO3 (65% m/v) and HCl
(37% m/v), Merck reagents, both purified
by sub-boiling distillation), and microwave
(Anton Paar Multiwave closed system) was
used to pseudo total digestion of trace elements (i.e. Cu, Cd, Co, Fe, Mn, Ni, and Zn).
All the samples showed almost total digestion, except for some presence of SiO2. The
procedure is explained in detail in Paper V.
16
For the speciation of TEs sequential extraction was applied; however, sequential extraction can only indicate the potential, rather
than actual, mobility of TEs bound to soil
and sediment (Ure, 1991; Bacon & Davidson, 2008). This approach has been applied to both sediment and soil samples as
described in Papers IV and V. The Community Bureau of Reference (BCR) scheme was
applied to the Lake Titicaca sediment samples (Paper V) and they were digested following the BCR sequential extraction procedur (Ure et al., 1993), obtaining the fractionation of exchangeable, acid soluble, reducible, oxidizable, and residual fractions (slightly modified in the last step).
5.2 Analytical experiments
5.2.1 Determination of major anions
For major anion analysis in groundwater and
surface water samples ion chromatography
was used at the Instituto de Investigaciones
Químicas (IIQ), Universidad Mayor de San
Andrés (UMSA) (Paper II) and at the Land
and Water Department at KTH (Paper III)
laboratories (Papers I, II, & III).
5.2.2 Determination of major cations and
trace elements
For major cations (Na+, K+, Ca2+ and Mg2+)
in the groundwater and surface samples
were determined with flame atomic absorption spectrometer (AAS, Perkin Elmer Analyst 100) at the laboratory of the IIQ at Universidad Mayor de San Andrés (UMSA, Bolivia) (Papers I, II, & III).
TEs and As concentrations in groundwater,
surface water, digested soils and crops were
determined using inductively coupled plasma
optical emission spectrometry (ICP-OES;
Varian Instruments, model Varian Vista Pro
Ax) at the laboratory of Department of
Geological Sciences, Stockholm University
(Papers I, II, III & IV).
5.2.3 Determination of trace element in
sediments
The metal concentrations in the sediment
extracts obtained at each step were determined using an atomic absorption spectrophotometer Perkin Elmer AAnalyst-100;
flame atomization (air/acetylene) was used
for high content of TEs (heavy metals), and
to determine lower concentrations, electrothermal atomization in a graphite furnace,
HGA-800, was used at IBTEN laboratories
(Paper V).
5.2.4 Quality control
Quality control was performed for all analyses (water: surface and groundwater, soil,
crop and sediment samples), which includes
both blank (blanks, spike blanks) and sample
(duplicate and spiked) control (Papers I, II,
III & IV).
5.3 Geochemical modeling
Aquachem software (v4.0) was used to build
a water chemistry database and PHREEQC
(Parkhurst & Appelo, 1999) modeling with
MINTEQ.v4 database (Allison et al., 1990).
Thermodynamic data for Ca- arsenate minerals and complexes were added from Bothe
and Brown (1999) and data for Mg complexes from Whiting (1992) were used to
explain the possible formation of complexes
and minerals related to Ca and Mg arsenate:
i) Calculation of saturation index (SI) was
made to predict and identify mineral phases
which are in equilibrium with aqueous phases in both surface and groundwater (Papers
I, II & III). Saturation index is defined as
follow: when SI= 0 a minerals is at equilibrium with the aqueous phase; when SI> 0, the
water is oversaturated with respect to a minerals and finally, when SI< 0, water is undersaturated with respect to a mineral
(Parkhurst & Appelo, 1999). ii) Calculation
of speciation was completed to understand
As species distribution of mass at equilibrium in aqueous phases among complexes and
redox couples (Papers I, II & III). iii) Calculation of speciation taking into account TEs
in equilibrium in aqueous phases which control the mobilization of As (Papers I, II &
III).
5.4 Statistical analysis
For bivariate statistics, Pearson´s correlation
matrix was carried out in Papers I, III, IV
and V; additionally, Spearman´s rank correlation was measured in Paper IV. Multivariate statistics approach was involved to understand the principal component analysis
(PCA) and hierarchical cluster analysis
17
(HCA) which were performed in Papers I
and V. Finally, extracted factors and eigenvalues and factor analysis (FA) were calculated in Paper II. The procedures are explained in detail in the papers.
5.5 Mineralogical investigations
The identification of minerals in selected
soils and profile samples was carried out by
powder X-Ray Diffraction (model Seifert
XRD 3003 TT, with Cu Kα1 (1.5418Å) radiation) to identify bulk mineral composition
at the Instituto de Geología y Medio Ambiente (IGEMA) at the Geology Department
of Universidad Mayor de San Andrés
(UMSA) in La Paz, Bolivia.
5.6 Environmental index assessments for soils, crops and lake
sediments
In order to evaluate in detail the TE data
base in different part of the ecosystems their
environmental risk values were calculated,
explanations are included in the respective
papers.
5.6.1 Availability ratio (AR) (Paper IV)
Availability ratio (AR) is used to estimate the
soil metal enrichment, or even a slow transformation to more stable forms that has
been discussed in previous studies (Massas
et al., 2009, 2010, 2013). Twenty seven samples paired between aqua regia and DPTA
extracts were evaluated (Massas et al., 2009).
5.6.2 Transfer factor (TF) (Paper IV)
The transfer factor, TF soil-to-plant (edible
part), is a measure of the uptake of trace
elements by plants from soil (Cui et al.,
2004; Rötting et al., 2013). The total of the
samples (n= 36) was included in the evaluation of TF, which included beans, barley,
potato and alfalfa; the soil and crop concentrations were measured on a dry weight basis, but the crop contents were converted to
fresh weight basis assuming a mean water
content of 90% (Rötting et al., 2013).
5.6.3 Risk assessment code (RAC) (Paper V)
The RAC is defined as the fraction of TE
exchangeable and/or associated with carbonates (%F1), this portion of the TE is
easily released to the hydrologic system
(Passos et al., 2010) and the values are interpreted in accordance with the RAC classification (Paper I). The range values were kept
in order to make a comparison with other
studies; nine (deep and shallow) sediments
were included in the assessment.
5.6.4 Geoaccumulation index (Paper V)
The geoaccumulation index (Igeo) is used to
determine the quantitative extent of TE pollution in sediments, this index is divided into
seven classes (Müller, 1981; Paper V). The
geochemical background value in average
shale was used to calculate the Igeo index,
nine sediments samples were taken in the
evaluation of Igeo.
5.6.5 Metal enrichment factor (Paper V)
The Enrichment Factor (EF) is a ratio between real and reference values and is an
estimation of anthropogenic input. The EF
values were calculated with respect to reference background concentrations relative to
Fe concentrations, and are classified on the
basis of the five ranges; Paper V). In this
study, the EF was calculated with respect to
reference background concentrations of Fe,
since the TEs are sorbed on its surface and
act as a quasi-conservative tracer of the natural metal-bearing phases in the sediments
(Schiff & Weisberg, 1999; Turner & Millward, 2000; Aprile & Bouvy, 2008). Nine
sediments were taken to calculate the EF
values.
6 R ESULTS
6.1 Groundwater and surface water
hydrochemistry in Poopó Basin
(PB)
6.1.1 Groundwater hydrochemistry
The field data set around the Poopó Basin
(PB) shows that the pH of the groundwater
is nearly neutral (7.2) in the samples without
contamination (range 6.40 – 7.90); except
the sample (29), SORP1 well, located in the
mining affected area (R-II) with pH 3.79 in
the dry season (Paper I). However, a detailed
groundwater survey of the Antequera and
Poopó sub-basins (regions II & III) indicate
that pH values are noticed between 6.6 – 9.7
(median, 8.1) in groundwater and 7.7 (medi18
an value) for thermal springs samples (Papers II & III) in the rainy season.
The Eh had values in the groundwater in the
range 142 to 218 mV along the PB indicating moderately oxidizing conditions in all
regions in the dry season (Paper I). Whereas
in the rainy season in the Antequera and
Poopó sub-basins, the ranges are -86.6 to
203.7 mV (median, 64.5 mV) in groundwater
and 28 to 142.7 mV (median 86.0 mV) in
thermal springs. The lowest Eh values are in
non-thermal groundwater samples GW-15 (8.3 mV), GW-27 (-12.8 mV), and GW-28 (86.6 mV), where the Eh values suggested
moderately reducing conditions in some
places, but oxidizing in others (Papers II &
III).
The EC values indicate different behaviors
in the PB, groundwater EC values varies in
all regions, for R-I from 0.9 – 2.1 mS/cm,
for R-II from 0.7 – 5.6 mS/cm, for R-III
from 0.2 – 1.2 mS/cm, for R-IV from 0.6 –
1.3 mS/cm, and from 0.6 – 3.8 mS/cm at RV in the dry season (Paper II). But, during
the rainy period in the Antequera and Poopó
sub-basins, the range of EC values in
groundwater is 0.13 – 3.50 mS/cm, except
GW-5 (13.47 mS/cm) and thermal spring
samples show the range 10.26 – 19.13
mS/cm (median, 17.24 mS/cm) (Papers II
& III).
6.1.2 Surface water hydrochemistry
The surface water samples located in the
headwater region(reported in Papers I, II &
III) show that a sample in the Antequera
sub-basin has a pH of 7.60 in dry period;
however, in the rainy season the pH range is
from 8.05 – 12.2 taking into account the
samples in both the Antequera and Poopó
sub-basins. All the surface stream samples
located in the headwaters of the basin are
dominated by baseflow. In contrast, along
the area affected by acid mine drainage
(AMD) and acid rock drainage (ARD) the
pH range does not show any significant difference between dry and rainy season (3.1 –
4.7; 3.3 – 5.2), respectively, in the Antequera
sub-basin; instead the range is 3.7 – 7.2 in
the Poopó sub-basin in the rainy season
(Papers II & III).
In surface water, comparison of Eh values
for both dry and rainy seasons in the Antequera and Poopó sub-basins shows that the
range does not seem to changes and the
range is 117 – 381 mV (Papers I, II & III)
in areas affected AMD/ARD). The samples
along the river affected by AMD/ARD
(from Bolivar tailings to outlet of the subbasin) could be governing the oxidation of
the solid material in the rivers bed during
both dry and rainy seasons. Nevertheless,
the samples located in headwaters show that
most of the surface water samples have
Figure 5. Piper plot showing the major ion chemistry of the water samples in: a) groundwater (wells) and b) surface water. Arrows in the plot indicate the possible pathway of
evolution of groundwater chemistry.
19
moderately reducing or reducing conditions
(Papers II & III).
water which shows high EC which is consistent with the field data.
The river baseflow in headwaters shows low
EC values 0.28 mS/cm (Paper I) and in the
range from 3.3 µS/cm to 0.51 mS/cm (Paper II & III) in the dry and rainy seasons,
respectively. However, occurrence of high
EC in surface water in the area affected by
ARD/ARD is directly related to the dissolution of minerals and, additionally, the combination with thermal springs to reach values
from 2.4 to 15.9 mS/cm in both seasons and
sub-basins (Papers I, II & III).
The surface water is predominantly of the
Ca–SO4 type at R-II, except for the sample
CHAO1 which is of the Ca–HCO3 type
located at the headwater area (Paper I). In
the rainy season, the samples from the
Antequera and Poopó sub-basins show various hydrochemical types: most samples fall
into the Na–Cl, Ca–Mg–HCO3–Cl, and Ca–
Mg–CO3 water type while the Ca–SO4 water
type (Fig. 5b; Paper II) coincides with affected areas by AMD/ARD.
6.1.3 Hydrochemical types and major ions in
groundwater and surface water
The Piper diagram for groundwater in the
dry season around the PB, for region I (R-I;
Fig. 5a) shows that the major ions in the
groundwater are Mg–Na–HCO3; for R-II
the dominant ions seem to be Ca–HCO3,
while others are Na–Cl and in the region
affected by mining activities shows Na–SO4
water type. In the regions R-III, R-IV and RV (Fig. 5a) Na–HCO3 are the dominant ions
in the groundwater samples followed by Na–
Cl (Paper I). During the rainy season in the
Antequera and Poopó Sub-basins, the
groundwater does not have a clearly predominantly water type; however, still Na–Cl
predominate in both sub-basins (Papers II &
III). The enrichment of Na+ and Cl- in the
groundwater samples could be linked to
halite dissolution or the influence of thermal
6.2 Geochemical
modeling
in
groundwater and surface water in
the Poopó Basin
The results of PHREEQC geochemical
modeling found that the ranges of calculated
log pCO2 values in the groundwater is -2.7 –
-1.5 (median, -1.9) during the dry season
around the PB; while in the rainy season
samples from the Antequera and Poopó
sub-basins indicate a range from -5.2 to -1.9
(median, -2.9). Furthermore, during the dry
season the samples are undersaturated with
respect to calcite and dolomite, the opposite
is true for both calcite and dolomite in the
rainy period (Papers II & III), except for few
groundwater samples in both sites.
The distribution of the SI values calculated
by the PHREEQC indicate that water was
between equilibrium and oversaturation with
Figure 6. Piper diagrams showing hydrochemical types of a) groundwater (solid
diamond Antequera, grey diamond Poopó) and b) surface water (solid squared
Antequera, open squared Poopó).
20
respect to ferrihydrite (Fe(OH)3) in the dry
season (Fig. 7a; Papers I & III). However, in
the rainy season, groundwater samples are
undersaturated with respect to rhodochrosite (MnCO3) and siderite (FeCO3) minerals (Fig. 7b, c; Paper III). Moreover, SI
values indicate that water is undersatudated
with respect to scorodite (FeAsO4:2H2O)
during both dry and rainy seasons (Paper
III).
In surface water, further evaluation of the SI
results in Paper III showed that the samples
of headwater from both the Antequera and
Poopó sub-basins are oversaturated with
respect to ferrihydrite. In contrast, in the
areas affected by AMD/ARD the SI results
suggest that the samples are undersaturated
at Antequera sub-basin, while in the Poopó
sub-basin they are oversaturated with respect
to ferrihydrite (Fig. 7c; Paper III).
The results from both dry and rainy seasons
indicate that the low values are related to
HCO3- and CO32- dissolution in groundwater
which could be due to carbonate (calcite or
dolomite) weathering and less associated to
organic matter oxidation (Mukherjee et
al., 2008; Papers I & II).
6.3 Trace elements in groundwater and
surface water in the Poopó Basin
6.3.1 TEs in groundwater
In groundwater, the concentrations of Cu,
Cd, Pb and Zn are low in the regions around
the Poopó Basin (PB), except in region II in
the dry season (Paper I). A detailed evaluation in the mining areas (region II) found
that the TE concentration (comparison of
median values) in groundwater follows the
order Zn> Fe> Mn> As> Cu> Cd in the
Antequera sub-basin, and Mn> Zn> As>
Fe> Cu> Cd in the Poopó sub-basin (Paper
III). The Cd concentrations exceed the
WHO guideline (i.e. 3.0 µg/L) in the Antequera sub-basin samples, while in the Poopó
Figure 7. Bivariate plots showing the dependency of the calculated Saturation Indices values for ferrihydrite versus Fe in groundwater, b) siderite versus Fe in
groundwater, c) rhodochrosite versus Mn in groundwater, and d) ferrihydrite versus Fe in surface water. Equiline shown at zero.
21
1.68 mg/L), Mn (median 12.05 mg/L), Zn
(median 116.5 mg/L) and Al (median 24.4
mg/L) in the area affected by AMD/ARD.
The surface waters in this affected area show
low As concentrations (<15 µg/L) (Paper I).
The TE concentrations are higher in the
surface water in Antequera sub-basin due to
the high acid pH of the river water.
In a detailed study of the surface water (Fig.
9), the order of concentration of the TEs in
surface water (comparison of median values)
was Zn> Fe> Cd> Mn> As> Cu in the
Antequera sub-basin (Paper III). This highlights the severity of the Cd contamination,
which could be explained by the huge
amoun of mining wastes abandoned along
the Antequera River (e.g. at Avicaya, Fig. 1).
The order of concentration for the Poopó
sub-basin is Fe> Zn> As> Mn> Cd> Cu
(Paper III).
Figure 8. Box and Whisker plots for
metals and TEs in groundwater regions;
a) region I, b) region II, c) region III,
d) region IV, e) region V and f) surface
water.
sub-basin samples show less Cd (median,
0.95 µg/L). For Cu the range is 1.0 – 8.15
µg/L (median, 2.8 and 2.4 µg/L in the
Antequera and Poopó sub-basins, respectively). However, Zn concentrations are in
the range 6.5 – 1318 µg/L (median, 107.5
and 25.2 µg/L in the Antequera and Poopó
sub-basins, respectively) during the rainy
period (Fig. 8a – e; Paper III).
6.3.2 TEs in surface water in the Poopó
Basin
The surface water samples (Fig. 8f; Paper I)
indicate high concentration of Fe (median
The headwater samples (SW-2, 3, 13 – 18)
show that the Cd concentrations are between b.d.l. (<0.46 µg/L) and 2.05 µg/L. In
the places where the samples are influenced
by thermal water the Cd concentration ranges from 0.58 to 2.22 µg/L; all of the samples
represent a mix of thermal water and river
baseflow. The samples influenced by
ARD/AMD along the Antequera and Poopó rivers are typical of mining areas with
high TE (Al, Cd, Cu, Mn, Pb and Zn) concentrations during both dry and rainy seasons (Paper III); furthermore, in a sample
taken near to the Tiwanaku tailing dam (SW22) indicates high Cd concentration in the
range 7.3 – 1855 µg/L (median, 155.9 µg/L),
Pb (239.3 µg/L) and huge concentrations of
Fe and Mn (Fig. 9c, d; Paper III).
6.4 Occurrence
of
arsenic
in
groundwater in the Poopó Basin
6.4.1 Arsenic in groundwater of Poopó
Basin
In the whole Poopó Basin (PB), the As concentration in the groundwater ranges from
below detection limit (b.d.l., 5.6 µg/L) to
242.4 µg/L (median, 41.4 µg/L; n = 28)
taking into account the whole database. In
order to better understand the As distribution the area was divided into five regions
22
Figure 9. Box and Whisker plot showing the distribution of As and trace
elements in a) Antequera groundwater, b) Poopó groundwater, and c) Antequera surface water, d) Poopó surface water.
based on previous studies (PAADO, 2005).
In the groundwater samples for R-I in the
northern of the basin (Paper I) the results
for As concentration are relatively low (b.d.l.
to 24.3 µg/L; Fig. 8a). However, for R-II in
the eastern area (Paper I) with mining activities the concentration of As ranges from
b.d.l. up to 185.7 µg/L (Fig. 8b) reaching
maximum concentration in well PAZP2
(185.7 µg/L). As concentrations in region III
(southern of Poopó Basin) are higher than in
other regions, these are located near the
Condo K and Quillacas towns, reaching
229.4 and 233.3 µg/L, respectively. In R-IV
(Paper I) the As concentrations range from
38.8 to 116.8 µg/L in the eastern side of the
basin. Finally, in R-V near Toledo located in
the northwest, the highest As concentrations
are 234.3 – 242.4 µg/L in the dry season
(Fig. 8a – e; Paper I).
6.4.2 Arsenic in groundwater in Antequera
and Poopó Sub-basin
In the detailed assessment of the rainy season in the Antequera sub-basin, the As concentration in groundwater samples (Fig. 9a,
b) are in the range from b.d.l. (5.6 µg/L) to
364 µg/L. The study has taken into account
three limits. First, WHO and Bolivian regulation in terms of safe drinking water guidelines (WHO & NB-512) up to 10 µg/L; secondly, the values of the maximum content in
the Bolivian Class A standard for discharge
to water bodies (50 µg/L) and, third, concentrations of As above the later limit. In the
Antequera sub-basin, two samples are below
the first limit, eight samples are below the
second limit (< 50 µg/L) and seven exceed
the Bolivian limit (>50 µg/L) reaching 364
µg/L as highest value. Meanwhile, in the
Poopó sub-basin, As concentration are in
the range from >10 µg/L to 104.4 µg/L.
Eleven samples do not exceed the second
limit, and only one sample shows high concentration than 50 µg/L (i.e. 104 µg/L).
Moreover, the As concentration in thermal
springs is in the range 34.1 – 45.2 µg/L
(median value, 38.9 µg/L) in both the Antequera and Poopó sub-basins (Paper III).
6.4.3 As in surface water in the Antequera
and Poopó Sub-basin
The As concentration in surface water in the
Antequera sub-basin (Fig. 9c, d) that is im23
Figure 10. X- ray diffraction of selected soils samples: a) three transect (T1,
T2, and T3) and profile POM2 (4, 7 and 9 m; deep), and b) standard magnesium arsenate mineral (Mg 2As 2O7).
pacted by ARD/AMD has relatively low As
concentrations (median, 9.7 µg/L), presumably because of As immobilization due to
co-precipitation/adsorption on ferrihydrite
surfaces, in the dry season (Paper I). The
headwater sample of the sub-basin shows
32.4 µg/L of As.
During the rainy period in the Antequera
sub-basin, two samples were found to have
As concentrations between b.d.l. and 10
µg/L, and ten samples fell in the range (10 –
50 µg/L), i.e. between the WHO/NB-512
guideline and the Bolivian regulation (50
µg/L). One sample exceeds the Bolivian
limit as it contains 248 µg/L As (SW-8). In
the Poopó sub-basin, two samples have As
concentrations between b.d.l. to 10 µg/L,
seven samples fell in the range (10 – 50
µg/L) and one sample exceeds all regulations (i.e. 30.7 As mg/L; SW-22, tailing leakage). The samples in the headwater of the
sub-basins show concentrations in the range
from b.d.l. to 34.3 µg/L As (Paper III).
PHREEQC results suggest that As is adsorbed more readily onto ferrihydrite in both
Antequera and Poopó sampling sites.
PHREEQC modeling results of speciation
suggest that Fe(II) concentrations in all surface water samples are greater than Fe(III) in
areas affected by ARD/AMD. Conversely,
Fe(III) concentrations predominate over
Fe(II) in the samples in the headwaters of
the basin.
6.4.4 Distribution of major redox sensitive
species (Fe and Mn) in groundwater
In the entire basin, the concentrations of Fe
and Mn groundwater are in the ranges 9.8 –
1,892 µg/L (median 22.5 µg/L), and 1.2 –
1,089 µg/L (median 7.3 µg/L), respectively
(Paper I). High concentration of Fe and Mn
are found at R-II in the alluvial plain and the
SO42- concentration is relatively low (9.1
mg/L, Paper I). The sources for increased
concentrations of these TEs may be wolframite ((Fe,Mn)WO4) veins reported by
Banks et al. (2004). However, low concentrations of these TEs are found in the other
regions (R-I, R-III, R-IV and R-V) with few
exceptions (Fig. 8a – e; Paper I).
24
Figure 11. Mean trace elements concentrations in soil. a) Aqua regia extraction method
(pseudo total concentration) and b) DTPA extraction method (bioavailable concentration),
values are on a (mg/kg) dry weight basis.
The results of the study in terms of redox
sensitive elements in groundwater indicate
that Fe shows diverse concentrations in the
mining areas in both sites. The concentration range of Fe at the Antequera site is 8.5
– 204 Fe µg/L (median, 51.3 µg/L), whereas
in Poopó the range is 3.6 – 74 Fe µg/L (median, 14.2 µg/L), except GW-22 (410 µg/L).
In thermal water in Antequera (GW-17) the
Fe concentration is 42.8 µg/L and 37.4 µg/L
in Poopó (Fig. 9a, b; Paper III).
Second, manganese concentration in the
Antequera site exceeds the WHO guideline
value (400 µg/L; WHO, 2011) in four samples. In Poopó the site, only one exceeds the
WHO guideline. In thermal water the Mn
concentration reaches 4.3 µg/L in the Antequera site and in Poopó (GW-27 and 28) it
reaches a maximum of 270 µg/L (Paper III).
Thermal water is used for recreational purposes at both Antequera and Poopó sites,
but is mixed with surface water (not
ARD/AMD) for irrigation purposes. In
surface water, high concentrations of Al, Fe,
Mn and Zn are found during both dry and
rainy seasons, meaning that the same process governs the release of TEs, the high
concentrations are results of dissolution of
abandoned waste, tailing leakage and weathering of sulfide minerals (Papers I, II & III).
6.5 Trace element concentrations in
soils (Paper IV)
6.5.1 Mineralogy and soil characteristics
X-ray diffraction of selected samples in the
three (T1, T2 and T3) transects revealed that
in T1 the predominant minerals were silicate
(quartz), alumino-silicates (muscovite, merlinoite and chlorites). The T2 transect also
shows silicate (quartz), alumino-silicates
(muscovite, albite and kaolinite), while for
the T3 transect silicate (quartz), aluminosilicates (anorthite, muscovite, and kaolinite)
and magnesium arsenate (Mg2As2O7) constitute the bulk. The presence of latter mineral
only occurs in the sample in T3 transect
(Fig. 10; Paper IV).
6.5.2 Soil type of studied region
The pH of the soil is moderately acid to
weakly basic in the three sites (total mean
6.57), mean values were 6.7, 6.4, and 6.61 for
T1, T2 and T3, respectively. The pH values
are homogeneous in the study area, meaning
that they do not depend on the either crops
or the soil factors. Soil texture is homogeneous among the transects, in the distributions
there are predominantly sand (T1: 27 – 56%,
mean 48%; T2: 17 – 56%, mean 46%; T3: 38
– 63%, mean 46%), silt (T1: 23 – 44%, mean
31%; T2: 20 – 54%, mean 35%; T3: 16 –
36%, mean 30%) and clay (T1: 16 – 28%,
mean 22%; T2: 16 – 30%, mean 22%; T3: 17
25
– 25%, mean 22%). The CEC values were
low (5 – 27 cmol[+]/kg), for T1 range 5.7 –
16.8 cmol[+]/kg (mean, 9.3), for T2 5.7 –
18.5 cmol[+]/kg (mean, 10.9), and for T3
5.8 – 26 cmol[+]/kg (mean, 11.3). The OM
contents were, for T1 0.5 – 2.3% (mean
1.1%), for T2 0.7 – 2.5% (mean 1.3%), and
0.6 – 2.2% (mean, 1.1%) for T3. The EC
mean values in the three transect were 0.12,
0.39, 0.34 dS/cm at T1, T2 and T3, respectively. The electrical conductivity (EC)
shows that in the T3 the values are higher
(0.34 dS/cm) than for the others (T1 and
T2) (Paper IV).
6.5.3 Extraction of major trace element in
soils
The Asregia concentrations range from 13 to
38 mg/kg (mean, 23.3) for T1; transect T2
shows 9.3 – 40.2 mg/kg (mean, 22.1); and
T3 transect 14.3 – 27 mg/kg (mean, 17.49).
The Cdregia concentrations in the soils range
from 0.2 to 2.1 mg/kg, with mean values of
0.52 mg/kg (range: 0.2 – 0.9) for T1; 0.65
mg/kg (range: 0.3 – 1.2) for T2; and 0.73
mg/kg (range: 0.2 – 2.1) for T3. For Curegia,
the concentrations range from 8.66 to 48.58
mg/kg, with mean values of 20.52 mg/kg
(range: 8.7 – 48.6) for T1; 21.04 mg/kg
(range: 9.4 – 41.1) for T2, 15.74 mg/kg
(range: 9.3 – 21.0) for T3. For Pbregia concentrations range from 15.8 to 138.7 mg/kg,
with mean values of 49.35 mg/kg (range:
20.4 – 104.4) for T1; 45.83 mg/kg (range:
15.8 – 85.9) for T2; and 45.54 mg/kg mg/kg
(range: 16.6 – 138.7) for T3. Znregia ranges
from 45.54 to 246.61 mg/kg, with mean
values of 92.99 mg/kg (range: 54.5 – 232.5)
for T1; 120.18 mg/kg (range: 58 – 203.0) for
T2; 96.78 mg/kg (range: 45.5 – 246.6) for T3
(Fig. 11a; Paper IV).
The univariate analysis includes the mean
and range and comparative mean tests were
carried out (Student t-test, one-way ANOVA) with 0.05 level of significance. ANOVA
test of extracts of aqua regia TEs (As, Cd, Cu,
Pb and Zn) reveal that there is no significant
difference among the three places (p> 0.05,
one-way) indicating their probably common
source.
6.5.4 Available trace elements extractions in
soils
There are different ranges for available TEs
(Fig. 11b), the range concentrations is 0.03 –
0.35 mg/kg for AsDTPA. The range of As
concentration in T1 is 0.04 – 0.12 mg/kg
(mean, 0.07); for T2 0.03 – 0.35 mg/kg
(mean 0.09); for T3 0.06 – 0.11 mg/kg
(mean 0.08). For CdDTPA available concentration is 0.02 – 041. The range CdDTPA concentration in T1 is 0.03 – 0.11 mg/kg (mean
0.06), for T2 0.03 – 0.39 mg/kg (mean 0.07),
for T3 0.02 – 0.41 mg/kg (mean 0.11). For
CuDTPA the concentration is 0.36 – 1.77. T1
transect range is 0.58 – 1.21 mg/kg (mean
0.91), T2 0.91 – 0.36 mg/kg (mean 0.78), T3
0.64 – 1.77 mg/kg (mean 1.07). For PbDTPA,
the full range is 0.20 – 1.66 mg/kg, in T1
0.48 – 1.66 mg/kg (mean 0.98), T2 0.42 –
1.64 mg/kg (mean 0.75), and T3 0.20 – 1.04
mg/kg (mean 0.55). The ZnDTPA full range is
0.13 – 36.81, T1 1.16 – 2.45 mg/kg (mean
1.67), T2 0.70 – 16.09 mg/kg (mean 4.96),
and T3 0.13 – 36.81 mg/kg (mean 7.00).
The univariate analysis includes the mean
and range and comparative mean tests were
carried out (Student t-test, one-way ANOVA) with 0.05 level of significance. The
ANOVA (0.05 level) indicates that there are
no significant differences between means at
the three studied sites for As, Cd, Cu, Pb
and Zn (Paper IV).
6.5.5 Sequential extraction of arsenic in soil
A sequential extraction procedure for As
was applied to selected samples (Wenzel et
al., 2001). Exchangeable As (readily available; step 1) ranges from 0.14 to 0.29 mg/kg
(mean 0.17) which represents less than 1.9%
(mean 0.8%) of the total As in the samples.
This fraction is indicating the most important As pool related to environmental
risk (Wenzel et al., 2001). The T3 transect
samples have slightly higher contents than
the T1 and T2 samples.
26
Figure 12. Trace elements (heavy metal) fractionation (F1 – F4) in sediments of Lake Titicaca.
27
For specifically sorbed As (step 2), the full
range constituted 0.60 – 2.84 mg/kg (mean
1.13). The As released in this fraction can be
potentially mobilized and directly take up by
plants due to competition between phosphate and arsenate for adsorption sites
(Wenzel et al., 2001; Niazi et al., 2011). As
associated to amorphous Fe oxides (step 3)
represents the largest pool with the range
from 4.29 – 12.06 mg/kg (mean 7.14). As
extracted from crystalline Fe oxides (step 4)
represents the range 2.30 – 9.96 mg/kg
(mean 6.05). The residual phase (step 5) has
a general range from 1.68 to 28.35 mg/kg
(mean 7.62) (Paper IV).
crops
The data for dry weight basis were converted assuming a mean water content of 90%
(Rötting et al., 2013) in order to compare
with Chilean and international regulations
(FAO, WHO, EC).
The As concentration in beans ranges from
0.19 to 0.24 mg/kgfw (mean 0.19); for Cd the
range is 0.02 – 0.05 mg/kgfw (mean 0.03);
and for Pb 0.077 – 0.499 mg/kgfw (mean
0.319). The concentrations in barley is 0.093
– 0.396 mg/kgfw (mean 0.172) for As, 0.008
– 0.029 mg/kgfw (mean 0.012) for Cd, and
0.038 – 0.401 mg/kgfw (mean 0.162) for Pb.
For potato the As concentration is 0.093 –
0.208 mg/kgfw (mean 0.122), Cd 0.008 –
0.044 mg/kgdw (mean 0.023), and Pb 0.038 –
0.493 mg/kgfw (mean 0.156).
The univariate analysis includes the mean,
median, range and variance; comparative
mean tests were carried out (Student t-test,
one-way ANOVA) with 0.05 level of significance. Results for As and Pb show that there
are no significant differences between mean
(p<0.05; one-way) in the four different
crops; while Student´s t-test (0.05 level) for
Cd shows that there is a significant difference in means between beans – barley and
barley – potato crops (Paper IV).
that in both sites the content of OM varies
between 1.5 – 5.6% and 6.1 – 13.2% in shallow and deeper areas, respectively. The recoveries are in the range 90 – 105%, and the
total extraction and sum of the fractions
indicate good agreement. The total TE concentrations vary as follows: Cu (6.7 – 55.5
mg/kg), Zn (14.9 – 940.9 mg/kg), Pb (29.7
– 161.2 mg/kg), Cd (0.3 – 3.2 mg/kg), Fe
(883 – 5941 mg/kg), Mn (83.3 – 622.1
mg/kg), Co (14.7 – 27.7 mg/kg) and Ni (6.1
– 20.6 mg/kg).
The TE concentrations show that Cd, Cu
and Zn were found from very low to moderate levels at all sampling locations. There is
a moderate contamination by Pb for all
sampling points except for S4, it coincides
with a high contamination level by Pb and
Zn; this was the place for transfer the minerals, loaded from train to boat and transported to Puno Harbor (Peru). Also, Ni contamination for all points appears to be very
high in some fractions.
Sequential extraction (Fig. 12) results show
that TEs associated to the exchangeable and
acetic acid soluble fraction (F1) decrease in
the order Fe> Mn> Zn>Pb >Co >Ni>
Cu> Cd. The TEs associated with the reducible fraction (i.e. bound to Fe and Mn oxides), fraction 2 (F2), decrease in the order
Fe> Zn> Mn> Pb> Cu> Ni> Co> Cd.
Metals associated with OM and sulfides,
fraction 3 (F3), decrease in the order Fe>
Mn> Zn> Pb> Cu> Co> Ni> Cd. The
metals associated with the residual fraction
(i.e. strongly linked with the crystalline structure of minerals) fraction 4 (F4), decrease in
the order Fe> Mn> Zn> Pb> Cu> Co>
Ni> Cd (Paper V).
7 D ISCUSSION
The composition of natural waters is closely
related to the composition of the rocks that
they contact, transform and partially dissolve
(Morel, 1983).
lake sediments (Paper V)
Nine sediments samples at different depths
(8 – 156 m) of Minor and Major Lakes show
28
7.1 Mechanisms controlling the hydrochemistry in the Poopó Basin
(PB) (Paper I)
The natural water composition is controlled
by both geochemical and geo-biological processes (not discussed here) (Morel, 1983).
The groundwater composition depends on
the bulk mineralogy of the aquifer sediment
as well as on chemical weathering, one of
the major processes controlling the geochemical cycle of elements (Morel, 1983).
During this process, rock and primary minerals become transformed to solutes and
secondary
minerals
(Stumm
&
Morgan, 1996). The pH of water is then
primarily determined by a balance between
dissolution of weakly acidic carbon dioxide
(CO2) and basic rocks, alumino-silicates and
carbonates (Morel, 1983).
Taking this into account, the geochemical
evolution of the groundwater around Poopó
Basin (PB) depends on whether the water
source is near to Eastern Cordillera or in the
alluvial fan of the PB. For the whole basin
the major anions follow the order HCO3- >
Cl- > SO42- and the major cations are Na+ >
Ca2+ > Mg2+ (Paper I). The existence of the
HCO3–Na water type can be due to cation
exchange, as reported by other studies
(Bundschuh et al., 2004; Ravenscroft &
McArthur, 2004; Bhattacharya et al., 2006a).
This also agrees with the calcite, kaolinite
clay mineral, dolomite and gypsum saturation indices (SI) calculated by PHREEQC,
Figure 13. Box and whisker plots showing the distribution of all the major ions
in a) groundwater and b) surface water.
Figure 14. Bivariate plots between a) Na + versus Cl - and b) Ca 2+ + Mg 2+ versus SO42+ H CO3- in groundwater samples.
29
Table 1. Ionic ratios of groundwater and surface water samples from the Antequera and Poopó
sub-basins (Ratio derived from meq values)
Ionic ratio
Antequera GW
Poopó GW
Antequera SW
Poopó SW
min max
mean
min
max
mean
min max
mean
min max mean
+
0.1
4.2
1.3
0.1
5.0
1.6
0.4
30.5
10.9
0.3
4.9
2.1
HCO /(Ca + Mg )
0.0
1.6
0.4
0.0
0.7
0.2
0.0
0.0
0.0
0.0
0.8
0.1
2+
2+
+
Ca + Mg /Na + K
3-
2+
-
2+
HCO3 / Ca
2+
0.0
2.4
0.5
0.0
0.8
0.32
0.0
0.01
0.0
0.0
1.03 0.16
2+
Ca /Na
+
0.1
4.2
1.2
0.1
4.3
1.5
0.4
34.2
11.4
0.2
4.1
2.0
2+
Mg /Na
+
0.0
1.1
0.3
0.0
1.0
0.3
0.1
1.5
0.9
0.0
2.0
0.8
2+
2+
2.2
8.5
5.5
2.2
12.0
5.8
2.6
52.3
12.0
1.6
12.4 3.8
0.5
9.4
2.4
0.8
5.5
2.4
0.7
6.2
1.7
0.6
3.4
1.5
0.1
0.5
0.2
0.1
0.5
0.2
0.0
0.4
0.2
0.1
0.6
0.4
0.4
1.5
0.9
0.6
1.9
1.1
0.6
3.7
1.7
0.6
1.4
1.0
0.0
0.9
0.3
0.0
0.7
0.3
0.0
0.0
0.0
0.0
0.6
0.1
0.9
26.9
10.7
4.2
19.2
9.1
2.2
68.6
25.8
1.6
93.2 16.1
Ca /Mg
2+
Ca /SO4
2+
Mg /Ca
-
Cl /Na
2+
2+
+
-
-
HCO3 /HCO3 + SO4
2+
Ca + Mg
2+
2-
as also reported by other authors (Banks et
al., 2004; Lilja & Linde, 2006; Selander &
Svan, 2007) (Fig. 13a).
In the entire PB, Na+ versus Cl- are strongly
positively correlated (r2= 0.8; Fig 14a) (Paper
I), indicating the presence of soluble halite
(NaCl) in the groundwater in the study area,
due to i) high evapotranspiration rate, ii)
precipitation of NaCl during the dry periods
and iii) dissolution of salty Quaternary sediments (Minchin, 1882; Coudrain-Ribstein et
al., 1995a, b; Argollo & Mourguiart, 2000;
Fornari et al., 2001; Zapata, 2011). The plot
HCO3- + SO42- versus Ca2+ + Mg2+ is less
correlated (r2= 0.7, Fig. 14b; Paper I) suggesting that dissolution of calcite, dolomite
and gypsum are reactions occurring in the
system as reported by other authors in the
PB (Banks et al., 2004; Lilja & Linde, 2006;
Selander & Svan, 2007). There are additional
sources of sulfate such as weathering of sulfide minerals due to the geological conditions of the study area.
7.2 Distinguishing
hydrochemistry
mechanisms in the Antequera and
Poopó Sub-basins (Paper II)
7.2.1 Discrimination between processes related
to groundwater chemistry
In groundwater samples, mean (Ca2+ +
Mg2+)/(Na+ + K+) ratios in the Antequera
and Poopó sub-basins were 1.3 and 1.6, re-
spectively (Table 1). For both sub-basins
there seems to be a limited enrichment from
the dissolution of silicate minerals. Weathering of carbonates does not seem to be a process controlling the hydrochemistry as indicated by Na+ + K+ versus HCO3- and because the mean values of the HCO3-/(Ca2+ +
Mg2+) ratio are relatively low (0.4 and 0.2 for
the Antequera and Poopó sub-basins, respectively; Fig. 15a, b). The bivariate plots
show two distinct trends, one along the y =
2x (Fig. 15a), which suggests that carbonate
mineral dissolution is limited in some samples, whereas the second trend indicates that
there may be a combination of carbonate
and silicate dissolution in so much as samples are located between the y = 2x and
y= x.
The scattered plot between Ca2+ versus Mg2+
and Ca2+ versus HCO3- (both axes Na+ normalized; Fig. 16a, b) suggests that although
many groundwater samples in the zone are
indicative of global silicate weathering, other
samples in the zone indicate evaporite mineral dissolution, whereas some samples between these zones and indicate the occurrence of both processes.
The cation exchange can be evaluated by
bivariate plots (Na+ - Cl-) versus (Ca2+ +
Mg2+)-(HCO3- + SO42-) (Fig. 17) where the
slope should be -1 (i.e. y = -x) (Jankowski et
al., 1998; Biswas et al., 2012). Hence, the
30
Figure 15. Bivariate plots for a) (Ca 2+ + Mg 2+) versus H CO3-, and b) (Na + + K+) versus
H CO3- in the Antequera and Poopó sub-basins. Open diamonds, groundwater samples, and
solid triangles, surface water samples.
slope values of -0.76 and -0.71 in the Antequera and Poopó sub-basins, respectively,
indicate that cation exchange is to some extent responsible for the composition of shallow groundwater. The higher correlation in
the (r2= -0.76) Antequera groundwa ter
samples in comparison to the (r2= -0.71)
Poopó samples also suggest that cation
exchange might contribute to the relative
enrichment of K+ in the Antequera groundwater (Mukherjee et al., 2009).
Scatter plots are shown in Figures 18 and 19.
There is a strong correlation between Na+
and Cl- in both groundwater (r2= 0.99; Fig.
18a, b) and surface water (r2= 0.97; Fig. 19a)
samples. This probably indicates both evaporation and the dissolution of paleolake salts
Figure 16. Bivariate plots for a) Ca 2+/Na + versus Mg 2+/Na +, and b) Ca 2+/Na + versus
H CO3-/Na + in the Antequera and Poopó sub-basins. Open diamonds; groundwater
samples and solid triangles; surface water samples.
31
Figure 17. Bivariate plots of H CO3- +
SO42- corrected Ca 2+ + Mg 2+ versus Cl corrected Na +. Solid diamonds, Antequera groundwater samples; open diamonds Poopó groundwater samples and
solid squares, Antequera and Poopó
surface water samples.
such as halite, as discussed by CoudrainRibstein et al. (1995a, 1995b), Argollo and
Mourguiart (2000) and Fornari et al. (2001).
In some groundwater samples the ratio between Cl-/Na+ exceeds 1 (Table 1), and indicates that the enrichment of Cl- in shallow
groundwater relates to anthropogenic
sources such as agricultural residues (Jack et
al., 1999) and to the atmospheric deposition
of previously re-suspended soil dust particles
originating from ore deposits (Goix et
al., 2012).
The plots HCO3- + SO42- versus Ca2+ + Mg2+
(Fig. 18c) in groundwater show poor correlation, suggesting that calcite, dolomite and
gypsum dissolution is limited in both subbasins. In contrast, surface waters in both
sub-basins show a strong correlation between HCO3- + SO42- versus Ca2+ + Mg2+
(Fig. 19b; r2 = 0.86 Antequera, r2 = 0.99 Poopó), which indicates that the dissolution of
calcite, dolomite and/or gypsum can be described by the following equations (Sun et
al., 2013).
CaMg(CO3)2(s) + 2H2O + 2CO2 → Ca2+ +
Mg2+ + HCO3(1)
CaCO3(s)+ H2O + CO2 → Ca2+ + 2HCO3(2)
The oxidation of sulfide minerals is suggested by data from GW-1 – GW-4 and GW-11
at the outlet of the Antequera sub-basin due
Figure 18. Bivariate plots for groundwater showing a) Na + versus Cl - (large
scale), b) Na + versus Cl - (small scale),
and c) H CO3- + SO42- versus Ca 2+ +
Mg 2+. Solid diamonds, Antequera samples; open diamonds, Poopó samples.
to the high concentration of SO42- and Zn.
However, this explanation is not consistent
with the near-neutral pH values. High SO42and Ca2+ concentrations at these sampling
sites may also be due to gypsum dissolution.
Thus, it appears that SO42- concentrations
are influenced by the reactions in Eqs (3)
and (4), which represent water-rock reactions that can take place due not only to the
attack of CO2 dissolved in the water, but
also by the attack of H2SO4 produced by
oxidation of sulfides (Sun et al., 2013).
3CaxMg1-xCO3(s) + H2CO3 + H2SO4 →
3xCa2+ + 3(1-x)Mg2+ + HCO3- + SO42- (3)
FeS2(s) + 7/2O2 +H2O → Fe2+ + SO42- + 2H+
(4)
32
are predominant Ca2+ > Na+ > Mg2+, whereas Na+ > Ca2+ > Mg2+ are predominant in
Poopó surface waters. The principal anions
are SO42- > Cl- > CO32- > HCO3- in Antequera and SO42-> HCO3- ≈ CO32- > Cl- in
Poopó surface waters (Paper II). Median
concentrations of Ca2+ and SO42- were much
higher in Antequera than in the Poopó surface water samples, indicating that gypsum
dissolution may play a major role in the
Antequera sub-basin. During both dry and
rainy seasons along the main stream (Antequera River) it is perceived that the predominant process is the oxidation of the wastes
abandoned on the banks of the river.
Figure 19. Bivariate plots for surface
water showing a) Na + versus Cl -, and b)
H CO3- + SO42- versus Ca 2+ + Mg 2+. Solid squares, Antequera samples; open
squares, Poopó samples.
7.2.2 Describing the processes in surface
water chemistry
During the dry season, the surface water
chemistry in the Antequera River in areas
impacted by mining activities has a particular
behavior, where almost all samples have
SO42- and Ca2+ as dominant ions at R-II (Paper I). The elevated SO42- concentrations in
the surface water reflect oxidation of the
mining wastes, consisting mainly of sulfide
minerals such as pyrite, and evaporation
enrichment around the eastern shore of
Lake Poopó.
During the rainy season, in the main stream
of the Antequera river the following cations
In surface water samples, mean (Ca2+ +
Mg2+)/(Na+ + K+) ratios in both Antequera
and Poopó sub-basins are 10.9 and 2.1, respectively (Table 1). Antequera samples
show a clear signal of dissolution of silicate
minerals, especially in waters affected by
AMR/AMD. Samples in the headwaters that
are not affected by mining activities show
high (Ca2+ + Mg2+)/(Na+ + K+) ratios (1.8 –
4.6), which indicate that dissolution of carbonate minerals exerts a dominant control
on the local hydrochemistry (Table 1).The
scattered plot between Ca2+ versus Mg2+ and
Ca2+ versus HCO3- (axes Na+ normalized;
Fig. 16) shows that surface water samples
indicate silicate weathering dissolution and
little dissolution of evaporites. Samples affected by AMD and ARD show high SO42/Cl- ratios (range 3 to 18), i.e. are SO42- enriched (Table 1).
Most surface water samples from the Antequera and Poopó sub-basins plot in the region dominated by rock weathering (indicated by a circle, Fig. 20). In the evaporationcrystallization dominated region of the
Gibbs ratio plot (Fig. 20, indicated by an
asterix), sample SW-6 from the Antequera
sub-basin is affected by ARD and AMD,
and sample SW-18 from the Poopó subbasin comes from the tailings area. The remaining three Poopó and two Antequera
samples plot between the rock weathering
and evaporation-crystallization domains.
33
Figure 20. Gibbs ratios to indicate processes controlling surface
water chemistry. Solid squares; Antequera samples, open
squares Poopó samples. Other values indicate (1) Mean US
precipitation, (2) Negro River, (3) Orinoco River, (4) Ganges
River, (5) Nile River, (6) Volga River, (7) Rio Grande, (8) Colorado River, (9) Jordan River and (10) World oceans (Gibbs,
1970).
7.3 Mobilization of trace elements
and As in the hydrologic system
Dissolution and formation of solid hydroxides and oxides are important in aquatic
chemistry of many metal ions, particularly Fe
and Mn that depend on pH (Morel, 1983).
But also other ligands such as carbonate,
sulfide or phosphate, whose free concentrations depend not only on pH, but also on
total complex concentration and concentrations of precipitating metals (Morel, 1983).
7.3.1 Mobilization of trace elements and As
in the groundwater environment in the
Poopó Basin (PB) (Paper I)
In PB, there is a considerable variability in
groundwater chemistry, redox conditions
and TEs and As, the groundwater shows
two different trends: first, samples with high
As concentrations (100-250 µg/L) in some
wells in both regions III and V, and second,
samples with low concentrations of As (up
to 55 µg/L) in wells in regions I, II, and IV
(Fig. 8).
In general, the low As and Fe concentrations
in the groundwater suggest that As distribution is controlled by the co-precipitation and
adsorption on ferrihydrite surfaces in a part
of the study area. The groundwater with
high As concentration in some sites of region II also reflects localized patches where
the process of desorption from Fe(III) oxides and hydroxides is possibly one of the
principal mechanisms controlling the mobility of As, due to moderately oxidizing conditions (Smedley & Kinniburgh, 2002). The
hydrous ferric oxide (HFO) adsorption on
surfaces is supported by modeling results
that reveal that the groundwater was oversaturated for Fe(III) phases such as ferrihydrite. In contrast, the groundwater was undersaturated with respect to all As minerals.
Thus, the poor correlation of As versus TEs
and As versus SO42-, has led to the conclusion that the distribution of As and TEs is
not well defined, but seems to be controlled
by surficial oxidation processes.
There are three different types of impact in
sub-basin and transects, which are summarized as: i) natural by geological fingerprint
(Tapia et al., 2012), ii) mining activities and
tailings (PPO-04, 1996), and iii) clearing and
debris uncovered (PPO-04, 1996).
34
in groundwater in the Antequera and
Poopó Sub-basins (Paper III)
Consequently, samples collected from the
study area indicate almost the same chemical
variability and to interpreted geochemical
mechanisms is complicated by the different
Figure 21. Eh – pH diagram in a) whole
Poopó Basin and b) Antequera and Poopó
sub-basins. Red numbers, groundwater
samples, and black numbers, surface water
samples. Green line show the evolution of
As(V) species in surface water samples
along Coro Coro river from headwater to
outlet sub-basin; blue line show the evolution of As(V) species from Bolivar tailing
to Avicaya sector before to mix with Coro
Coro rivers until sub-basin outlet.
sources of contamination, which sometimes
overlap each other. The seasonal variation in
the transportation of TEs by re-suspension
of soil dust and dry deposition (Goix et
al., 2011), on soils by wind has not been
evaluated in this work.
It is worth mentioning that TE and As mobilization will be discussed in this section.
The factor analysis approach was used to
better understand the relationship between
parameters. In groundwater in the Antequera Sub-basin, five factors explained most
of the total variance in the geochemical data
set (86.7% of the variance; Paper III) from
groundwater samples (Fig. 21 and 22). Trace
elements show a positive loading in all the
cases for both factors 2 (20%) and 3 (14%)
which suggests the weathering of minerals
(plagioclase, evaporates, calcites, and gypsum) as controlling the release of major TEs
(Al, Fe, and Mn); the negative correlation of
Al and Fe with respect to pH suggests the
pH dependency of mineral solubility. The
negative correlation between Eh and pH
would seem to be due to the thermodynamic
stability of water, and the positive loading
for SO42-, Ca2+, Mg2+ and Mn, may represent
gypsum dissolution (Coudrain-Ribstein et al.,
1995a, 1995b). Factor 4 (10%): the positive
loading for Cd and Zn may indicate remobilization of TEs from hydrous ferric oxide
(HFO) surfaces. Cd is more chalcophile than
Zn and tends to persist in a sulfide while
ZnS is weathering (Fuge et al., 1993) which
explains its relative immobility in surface
soils in the present study (Paper IV), as was
observed in the CdDTPA and ZnDTPA extracts.
Factor 5 is probably related to competing
adsorption sites between As and PO43(Signes-Pastor et al., 2007). This finding is
also supported by the As speciation in soils,
for As specifically sorbed; it is the fraction
potentially mobilized as a result of competition between phosphate and arsenate adsorption sites, due to changes in pH or
phosphate application to soils (Wenzel et al.,
2001; Niazi et al., 2011).
35
Figure 22. Factor loadings for
different geochemical parameters
in Antequera groundwater. Loading values ≥±0.5 represent a significant contribution of the corresponding parameter (Paper III).
Figure 23. Factor loadings for different geochemical parameters in Poopó
groundwater. Loading values ≥±0.5 represent a significant contribution
of the corresponding parameter (Paper III).
36
In Poopó groundwater samples (Fig. 21 &
23), four factors explained most of the total
variance in the geochemical data (83.9%;
Paper III). TEs show a positive loading in all
factors. Factor 1 (42%) shows a positive
loading for EC, Cl-, SO42-, Al, K+, Mg2+, Na+
and Si, suggesting the weathering of minerals
(plagioclase, evaporates and carbonates).
Factor 2 (18%), has positive loadings for Eh,
alkalinity, Ca2+, and Fe and negative loadings
for pH and Cd, which may represent the
dissolution of calcite and consequently increasing the Fe solubility at low pH and also
the precipitation of Cd (CdCO3) (Rötting et
al., 2006) with enrichment of this TE in the
solid phase. Factor 3 (14%) has positive
loadings for alkalinity, As, Cd, Mn and Si,
showing first that Cd can be inmobilized by
precipitation as carbonate and second suggesting that dissolved HCO3- and Si may act
as competitors for As at the adsorption sites
on Mn and Fe hydroxides (Anawar et al.,
2004), thereby increasing the As dissolved in
groundwater. Finally, factor 4 (10%) indicates the dissolution of gibbsite and therefore the mobilization of TEs (Al and Zn).
in surface water (Paper III)
On the main stream samples from the Antequera sub-basin, factor analysis was carried
out and four factors explained 91.5% of the
variance in the data set (Fig. 21 and 24). Factor 1 (51%) has positive loadings for EC,
Eh, SO42-, Al, Cd, Mg2+, Si and Zn, and negative loadings for pH and alkalinity. This
suggests three geochemical processes: i) the
weathering of plagioclase, ii) the mobilization of TEs due to the dissolution of minerals at acidic pH, and iii) the oxidation of
sulfide minerals. Factor 2 (17%) has positive
loadings for EC, SO42-, Ca2+, Cd, and Mn,
and negative loadings for pH, alkalinity and
PO43-. This can be linked to the dissolution
of gypsum, both factors are linked to weathering of plagioclase, gypsum and evaporite
(Coudrain-Ribstein et al., 1995a, 1995b)
minerals at acidic pH. Factor 4 shows positive loadings for As and Fe, which is linked
to the adsorption of As onto Fe hydroxides
and to As and Fe mobilization when these
precipitates re-dissolve. Therefore, factors 1
and 2 make it possible to distinguish between dissolution processes in addition to
TE mobilization in different areas of the
Antequera sub-basin.
Four factors also explain most of the variance (96.0%) in the Poopó surface waters
(Fig. 21 and 25). Factor 1 shows a positive
loading for TEs (Al, As, Cd, Fe, and Zn).
These could be linked to three different geochemical processes: i) the weathering of plagioclase and dissolution of halite and gypsum, ii) the mobilization of TEs due to the
dissolution of minerals at acidic pH (most
waters were probably later mixed with more
alkaline waters, therefore explaining the lack
of correlation with pH), and iii) the dissolution of gypsum and halite. Factor 4 (6%)
shows a low positive loading for EC and
Mn. However, Factors 3 and 4 only explain a
very small fraction of the total variance and
can therefore be considered as having only
little significance in the geochemistry in the
Poopó sub-basin (Paper III).
7.4 Mobilization of trace elements
and As in transect soils
(Paper IV)
7.4.1 Mineralogical description of soils
The X-ray diffraction patterns are similar
along the three locations, quartz, muscovite,
and kaolinite constitute the bulk mineral in
the three transects. But there are also other
minerals such as merlinoite and chlorites in
T1, in T2 calcium-albite and in T3 anorthite
and magnesium arsenate (Mg2As2O7). The
latter is identified by X-ray diffraction as an
intensive signal in position 2Θ at 28.54, its
presence in this sample and no others samples is remarkable (Fig. 10). The occurrence
of kaolinite in inundated alluvial plains indicates the ultimate chemical alteration of the
predominant silicate rocks present in the
three sites (Fig. 10). The resolution of the Xray diffraction and the sensitivity of the radiation source (CuKα) used in the current
study was not suitable for identification of
other Fe-hydroxide minerals. Comparative
analysis of the three transects shows no variations which is also true for the profile samples in the Poopó alluvial fan (POM2, 4, 7
and 9 m deep) (Paper IV)
37
Figure 24. Factor loadings for different geochemical parameters in
Antequera surface water. Loading values ≥±0.5 represent a significant
contribution of the corresponding parameter.
Figure 25. Factor loadings for different geochemical parameters in Poopó surface water. Loading values ≥±0.5 represent a significant contribution of the corresponding parameter.
38
7.4.2 Characteristics of trace elements in
soils: trends with aqua regia extractions
In the current work, the contents of TEs in
aqua regia extracts show that As, Cd, Cu and
Pb are lower than the median values reported by PPO (1993-1996), only the Zn contents are slightly higher than those in the
PPO (1993-1996) report. The present study
and the PPO data base are directly comparable due to use of a similar extraction
method. In comparison with world soils
database, contents of As, Cd, Pb and Zn are
higher, while the concentrations of Cu is
lower than the average values for world soils
(Han, 2007), suggesting that the three areas
have high background content of TEs,
probably related to geologic conditions in
the Eastern Cordillera with the presence of a
polymetallic (Ag-Pb-Zn-Sn-Sb) belt in this
mining district (Arce-Burgoa & Goldfarb,
2009; Tapia et al., 2012) (Paper IV).
Pearson´s correlation is slightly positive
among aqua regia extracts of TEs (r2> 0.43)
(As-Cd, Cu, Pb, Zn), (Cd-Pb, Zn), (Cu-Pb,
Zn), (Pb-Zn), it could indicate a similar geochemical behavior and/or common source
material of these elements (Burak et al.,
2010) (Paper IV). The correlation between
Fe/Mn-As, Cu, Pb and Zn (p< 0.01) seems
to be related to the formation of secondary
iron oxides with capacity to strongly adsorb
these TEs, as already described in the literature (Burak et al., 2010).
7.4.3 Characteristics of trace elements in
soil: trends with DTPA single
extraction
Significant positive Pearson´s and Spearman´s rank correlations are found among
the available TEs, indicating that these TEs
are potentially available for plants (Hong et
al., 2008). Meanwhile comparing with physical-chemical characteristics only the OMAsDTPA shows a correlations significant at the
p< 0.01 level (Spearman’s rank), suggesting
that this As could be linked to OM. Furthermore, carbonate species are also established as potentially bioavailable, but the
slightly negative (r2= -0.51; p< 0.01) Spearman´s rank correlation between soil pHAsDTPA suggests that the retention of TEs as
carbonate is not dominant, this matches the
results of step1 (As fractionation)
(Paper IV).
7.4.4 Characteristics of arsenic in soils:
trends with sequential extractions
Arsenic easily released from non-specifically
adsorbed sites in the soils can be found in
fraction 1, for As associated to carbonates
and according the results of Pearson´s and
Spearman´s correlation their presence is not
predominant in the solid phase in the study
area, but this fraction represents the As concentrations (< 0.29 mg/kg; mean 0.17) that
can be used for predicting solute As, and is
useful for risk assessment of As leaching to
the aqueous phase (Wenzel et al., 2001). The
relatively high content in the T3 transect can
be supported by the XRD soil results, it can
be a source of As from dissolution of
Mg2As2O7 mineral (Paper IV).
The Asstep-2 specifically sorbed can be potentially mobilized due to pH and phosphate
concentration in soil and according to competition between phosphate and arsenate for
adsorption sites discussed in paper III (factor 5), elevated phosphate concentrations in
soil effectively de-sorb As(V), increasing
dissolved As concentrations (Signes-Pastor
et al., 2007) (reactions #12.1, #12.2; Paper
III). The soluble phosphate in soil ranges
from 5.95 to 15.54 mg/kg in the T3 transect
(Paper IV).
The last three fractions constitute the largest
pool of As (~ 90%), suggesting that As associated to amorphous Fe oxides is the main
source (F3= F5> F4; Paper IV) of As release due to changes of pH, redox, OM and
environmental conditions (minerals and
drainage).
7.4.5 Mobilization of trace elements in lake
sediments
The sedimentation dynamics are still poorly
known, in the case of carbonate deposits
Boulangé et al. (1981) give a rate of 0.5
mm/year for Lake Major and 10 times higher for Lake Minor; the rates are controlled
by the relation between allochthonous elements of detrital origin and autochthonous
39
elements of biogeochemical origin (Rodrigo
& Wirrmann, 1992).
Both deep and shallow sediment of Lake
Titicaca has shown varying TE spatial distribution based on the geological evolution and
anthropogenic conditions around the lake.
Earlier studies by Iltis et al. (1992) revealed a
predominantly anoxic environment in the
sediments of both the Lake Major and the
Chua depression in the Lake Minor, which
linked to OM in sediments that can cause
the mobilization of species that otherwise
would be retained by adsorption due to high
CEC values (Paper V).
There is a greater content of higher heavy
metals in the Lake Major than in the Lake
Minor. This is consistent with the fact that
Lake Major receives on average nearly 85%
of the total inputs of dissolved salt compared to only 15% for Lake Minor (Carmouze et al., 1992). The total dissolved salt
concentration varies from 0.9 g/L in Lake
Chucuito (Lake Major) to 1.2 g/L in Lake
Huiñaimarca (Lake Minor), meaning that the
waters are dominated by Cl-, SO42- and Na+
(Carmouze et al., 1981; 1992).
The behavior of the TEs in the lake sediments is special. The Fe partitioning (Paper
V) in the sediments follows the order: F4>
F3> F2> F1. S1 and S4 samples show higher content in F4, but other samples show
almost the same relative low content, suggesting that this could be considered a background value (Rodrigo & Wirrmann, 1992).
The lower content of Fe in the F3 fraction is
related to great photosynthetic activity of
phytoplankton and abundant macrophytes
(Iltis et al., 1992) in samples S7, S8 and S9.
The Mn partitioning in the sediments follows the completely opposite order to the
distribution of Fe: F1> F2> F3 >F4 (Paper
V). It is possible that the formation of
MnCO3 (Karageorgis et al., 2009) occurs in
the (S1, S5 and S6) samples related to the F1
fraction. In contrast, the mineralization of
fraction F3 could easily release Mn to the
water column in samples S3 and S4.
The Cu partitioning in the sediments follows
the order F3> F4> F2> F1 (Paper V). The
Cu bound to OM is well-known in geochemistry (Pempkowiase et al., 1999; Gonzáles et al., 2009), which under oxic conditions can be remobilized to the water column. The riparian towns are the main source
of domestic residues in S3, S4, S5 and S6.
However, the low content in S7, S8 and S9
in F3 seems to be due to slightly higher pH
values and photosynthetic activities (Iltis et
al., 1992) taking up Cu, which explains the
lower Cu available in fraction F1 (< 4.16
mg/kg).
The behavior of Ni is highlighted due to the
fact that almost all Ni is extracted in the first
three fractions, which can be easily remobilized by changes of environmental conditions (pH, redox potential, dissolved oxygen,
etc.). Nickel occurrence in the sediments
follows the order: F3> F2> F4> F1
(Paper V).
Zn partitioning gives the order F1= F2>
F4> F3 (Paper V). The same content is
found in the F1 and F2 fractions; in contrast, it is high in samples S1, S4 and S5 due
to mining activities in these representative
places (Passos et al., 2010). Zinc may be coprecipitated with isostructural carbonates,
e.g. siderite (FeCO3). Additionally, the content of Zn in oxides/hydroxides is consistent with the observed chemical fractionation of Zn in F2 (Ettler et al., 2006). Again,
S7, S8 and S9 show low content; it could be
explained by high macrophyte activity that
takes up Zn.
Lead is mostly associated to the residual and
oxidizable fraction (F3> F4> F2> F1; Paper
V) and Cd fractionation indicates that the
main portion is associated to OM phases
(S2, S4, S7, S8 and S9; F3> F2= F1> F4).
Cd can adsorb onto Fe and Mn oxides that
are found in S4 in fraction F2; meanwhile F1
(exchangeable and carbonate fraction) is
related to shallow sediments with high macrophyte activities (González et al., 2009).
The partitioning of Co in the sediments follows the order F1> F3> F4> F2. The remobilization of Co from sediment to water
occurs under anoxic conditions and stops
when the water becomes oxic (Petersen et
al., 1997) (Paper V).
40
7.5 Arsenic and other trace elements
in crops
Among the countries in Latin America few
have legislation and health considerations
concerning TEs in food; many countries
have no legislation on these points, and neither does Bolivia, so the comparison will be
made with international regulation (FAO,
WHO, EC). The discussion in this section is
limited to three TEs (i.e. As, Cd and Pb) due
to their toxicity to human and also to plants
(McBride, 1994; Kabata-Pendias & Mukherjee, 2007).
Arsenic
Queirolo et al. (2000) concluded that potatoes (including skin) constitute an efficient
bioaccumulator of As with a maximum concentration of 0.86 mg/kgfw, while beans
showed a maximum concentration of 0.112
mg/kgfw. Muñoz et al. (2002) determined
that concentrations of As in the skin was
between 3 to 70 times greater than the levels
in the edible part, for potato the ratio is 3
times, the concentration in the edible part is
0.021 mg/kgfw. Comparison with the contents found in the edible part in the present
study shows the following concentration of
As to be: beans and alfalfa (0.19 mg/kgfw) >
barley (0.17 mg/kgfw) > potato (0.11
mg/kgfw). The total mean (i.e. taking into
account all the crops analyzed in this study)
As content is 0.16 mg/kgfw; no samples exceed the tolerable limits for crops. The Chilean regulation for food (Muñoz et al., 2002)
establishes 0.5 mg/kgfw, for cereals and legumes, and 1.0 mg/kgfw for other products.
The contents measured here are fivefold
below the regulations. Also, these As contents are lower than those found in a review
database (mean: 6.22 mg/kgfw; range: 0.005 –
56.9 mg/kgfw) reported by Rötting et al.
(2013). Additionally, the ANOVA also depicts that there is no a significant difference
between As content in crops (p>0.05, oneway). The t-test (0.05 level of significance)
finds that for As there is a significant difference between beans and potato. Additionally, TEs in potato skin and broad bean skin
have dietary significance when potato and
broad beans are baked with the shell (Queirolo et al., 2000).
Cadmium
The range for Cd in different crops varied
from 0.0002 to 0.040 mg/kgfw in Chile
(Queirolo et al. 2000). In potato the Cd
mean concentrations is 0.0094 mg/kgfw, and
broad beans show 0.0033 mg/kgfw (Queirolo
et al., 2000). Oporto et al. (2007) reported a
Cd concentration of 0.21 mg/kgfw in potatoes in contaminated soils in the agricultural
valley at Pilcomayo River, where 81% of the
samples exceed the international regulations.
In this study, Cd mean contents are: beans
(0.03 mg/kgfw) > potato (0.023 mg/kgfw) >
alfalfa (0.017) > barley (0.012 mg/kgfw). The
mean global Cd content is 0.021 mg/kgfw,
not exceeding the international (FAO,
WHO, EC) regulation guidelines which establish limits for potatoes (peeled) and
stem/root vegetables (0.10 mg/kg, fresh
weight) and other vegetables (0.05 mg/kg,
fresh weight) (JECFA, 2005; European
Commission Regulation (EC-1881), 2006).
Lead
The range for Pb in different crops varied
from 0.0006 to 0.094 mg/kgfw (Queirolo et
al., 2000). The Pb total mean concentration
in the crops is: for alfalfa 0.025 mg/kgfw, for
potato 0.011 mg/kgfw , for broad beans 0.023
mg/kgfw. (Queirolo et al., 2000). In this
study, high Pb contents are found in beans
(0.32 mg/kgfw) > alfalfa (0.22 mg/kgfw) >
barley (0.16 mg/kgfw) ≈ potato (0.16
mg/kgfw). The European regulation guidelines have a maximum level of 0.20 mg/kg
(fresh weight) for cereal and legumes (barley,
alfalfa and beans), and 0.10 mg/kg for
peeled potatoes (European Commission
Regulation (EC-1881), 2006). The beans,
alfalfa and potato exceeded the limit for
cereal, legumes and potato values. The total
mean value (0.19 mg/kgfw) found in our
study is higher than the international regulations by ~ two fold. These Pb contents are
much lower than the data in the review database (mean: 3.28 mg/kgfw; range: 0.03 –
43.5 mg/kgfw) reported by Rötting et al.
(2013).
41
The statistical analyses were particularly interesting in one-way ANOVA (p< 0.05) for
As, Cd and Pb, which determined that there
are no significant differences in mean values
between crops for As an Pb, but there is a
significant difference for Cd contents between crops. Additionally, Student´s t-test
(at p = 0.05) for Cd found that there are
significant differences between mean concentrations for beans versus barley and barley versus potato crops.
7.6 Environmental index assessment
The results of the present work reveals that
the TEs can mobilize from soil-water (surface and groundwater) (Papers II, III & IV),
soil-crop (edible part) (Paper IV) and sediment-water (Paper V).
7.6.1 The relationship between As and TEs
in water (Papers I, II &III)
The groundwater show a nearly neutral pH
(7.2) around the PB and in the Antequera
and Poopó sub-basins basic pH (median 8.1)
(Paper I) and in both sub-basin moderately
reducing in some places, but oxidizing in
others (Papers II & III); this groundwater
characteristics govern the chemistry of TEs
around the studies areas. In PB, concentration of As was found in the range of 100 –
250 µg/L in the southern region (III) and in
the northwestern region (V), whereas it was
below 50 µg/L in the other regions (I, II and
IV) and the concentrations of Cu, Cd, Pb
and Zn are low in the regions around the
PB, except in region II in the dry season
(Paper I). A detailed study in Antequera and
Poopó sub-basins reveals that As, Cd and
Mn concentrations exceed World Health
Organization (WHO) drinking guidelines
(respective values: 10 µg/L, 3 µg/L and 400
µg/L; WHO, 2011), but Cu, Pb and Zn do
not (Paper III). The factor analysis reveals
that the mobilization of TEs in groundwater
is due to weathering of minerals (plagioclase,
evaporates, calcites and gypsum) which released TEs, and desorption from hydrous
ferric oxide (HFO) surfaces (factor 4; Antequera sub-basin) and competition between
As-PO43- (factor 5) in Antequera sub-basin
and As-HCO3- and As-SiO44- (factor 3) in
Poopó sub-basin. The As concentration in
groundwater can be related to the amount of
the As extracted in the steps 1 and 2, fractions mobilized due to changes of pH and
phosphate concentrations in the soils, which
agree with the factor 5 that show a competition between phosphate and arsenate for the
adsorption sites. All the surface stream samples located in the headwater of the basin are
dominated by baseflow and show a range
pH of 9.1-12.3 (median11.6) (Papers II and
III). In contrast, along the area affected by
AMD and ARD the pH range does not
show any significant difference between dry
and rainy season (3.1 – 4.7; 3.3 – 5.2), respectively, in the Antequera sub-basin; instead the range is 3.7 – 7.2 in the Poopó
sub-basin in the rainy season (Papers II &
III). In surface water, comparison of Eh
values for both dry and rainy seasons in the
Antequera and Poopó sub-basins shows that
the range does not seem to changes and the
range is 117 – 381 mV (Papers I, II & III) in
areas affected AMD/ARD). The headwater
samples (before flowing through areas with
mining activities) shows that the As concentrations are < 20.5 µg/L, Cd are less than 2.5
µg/L and in the thermal water As <45 µg/L
and Cd <1.2 µg/L. The surface water samples in Antequera sub-basin indicate high
concentration of Zn>Fe>Cd>Mn>As>Cu.
The high contamination of Cd could be explained by the huge mining wastes abandoned along the Antequera River. The order
of concentration for the Poopó sub-basin is
Fe> Zn> As> Mn> Cd> Cu (Paper III).
The drinking water concentrations show
concentration for As < 17 µg/L, for Cd <
1.1 µg/L and for Mn < 7.7 µg/L. The factor
analysis reveals that the mobilization of TEs
is governed also by weathering of (plagioclase, evaporates, calcites and gypsum) and
oxidation of sulfides enhanced at the acidic
pH (~3.4) in Antequera and Poopó subbasins. The above presented indicated that
in studied areas in Bolivian Altiplano there is
an elevated risk to ingestion to TEs in both
drinking water and probably dermal exposure via recreational thermal waters. The
exposure to TEs most of them naturally
present in the environments (e.g. As, Cd and
Mn) via ingestion (drinking water (Papers I,
42
Figure 26. Concept model of the occurrence of As and others TEs in groundwater, surface water and thermal springs in mining areas in Bolivia Altiplano.
II and III), food (Paper IV), inhalation (i.e.
dust) and dermal, can cause both noncarcinogenic and carcinogenic health consequences to the human body (Kapaj et al
2006; Nordberg 2009; Hughes et al., 2011;
Hug et al., 2011; Halder, 2013 and ref. there
in) (Fig. 26).
7.6.2 Index with respect to TEs in soils and
crops (Paper IV)
For DTPA extracts, based on the definition
availability ratio (AR), the DTPA extraction
show that less than 2% for As; <33% for Cd
(except in one sample, 80%); <9% for Cu;
<11% for Ni; <5% for Pb and <10% for
Zn (except in one sample, 48%) (Paper IV).
The soils show a low ratio of enrichment for
Cu, Pb and Zn, meaning the availabilities of
those TEs are limited; however, Cd concentrations show a particular behavior with a
high ratio from 11% to 33% indicating that
the plant-available fraction for Cd is relatively high. Tapia et al (2012) found that Cd
concentrations are higher in Eastern Cordillera surficial soils, and Fuge et al. (1993)
concluded that Cd is more chalcophile element than Zn and tends to persist as a sulfide while ZnS is weathering. Therefore, Cd
became enriched relative to Zn in the soil
which explains its relative immobility in surface soils.
Furthermore, it is worth considering that
most of the As (%) in these soils was extracted with ammonium oxalate (fractions 3
– 4), possibly indicating the association with
Fe and Al oxides; meaning that these results
confirm the crucial role of Fe and Al oxides
in immobilizing As. However, high contributions of the fixed As fraction, (i.e. F3, F4,
F5) should be considered as beneficial from
the aspect of environmental risk. The
amounts of As in fraction 2, which indicate
surface-bound As species and inner-sphere
surface complexes of As constitute < 10%
of the total As, a potentially mobilized fraction, which could be transferred to crops or
dissolved in groundwater. Therefore, the
environmental risk should be evaluated as
low.
43
The quality of irrigation water is also studied
in the present work, sodium adsorption ratio
(SAR) and percentage of sodium (Na%)
determine the suitability of water for irrigation purposes, and reveal that although
many SAR´s values for surface water and
groundwater are acceptable, high Na% of
the sampled surface waters is adverse for
crop growth. Even though some waters in
the Antequera sub-basin are composed of a
mixture of thermal water and runoff, Na%
values are still too high for irrigation use.
7.6.3 The relationship between TEs in soil
and crops: assessment of transfer
factor (Paper IV)
The transfer factor (TF) is an indicator of
the amount of TEs in the edible part of
crop, calculated values show different ranges
for As (0.002–0.020), Cd (0.09–0.143), and
Pb (0.0003–0.02). The means values of TFAs
are 2% for beans and barley, 0.8% for alfalfa, and 0.6% for potato, indicating that only
a small fraction is transported from roots to
the edible part compared with the 10%
available As (in step 2, Paper IV) suggesting
that As can be accumulated in the root rather than in the edible parts. This is based
on finding that As can be accumulated in the
soils due to amorphous and crystalline Fe
oxides surfaces present in the soils, which
was confirmed by the fixed arsenic determined fractions (fractions 3, 4, and 5) and
also for the aerobic conditions favorable to
barley cultivation, where less mobile As(V)
prevails with resulting retention of As
(Williams et al., 2007).
The mean values of TFCd are 6.8% for beans,
2.2% for barley, 4.7% for potato and 3.8%
for alfalfa. The uptake of Cd in presence of
high Cd available concentrations support the
findings that agree with Oporto et al. (2009),
due to the relatively high available CdDTPA in
the soils and low concentrations in barley
crops.
The mean values of TFPb are much lower
than those for Cd, varying from 0.9% for
beans to 0.5% for barley, potato and alfalfa,
indicating that much of the Pb available
could be fixed and retained in the roots (Paper IV).
7.6.4 Sequestration and mobility of TEs in
lake sediments
Risk assessment code (RAC) (Paper V)
In general, the sediments show from low to
moderate risk for Cu and Fe; moreover,
moderate to high risk for Zn, Pb, Cd, Mn,
Co, and Ni, these values were determined
based on the percentage of the total metal
content present in the first sediment fraction
(F1), and their presence may result in a serious impact on the aquatic ecosystem with
metals easily able to enter the food chain. In
the S1 sample, Pb is not dissolved and in S2
Cu, Zn, and Fe are strongly bound and not
easily mobilized into the aqueous phase.
Sample S3 shows that Cu, Pb, and Fe present a low risk for release into the water
column. The S4 sampling site shows that Cu,
Pb, Cd, and Ni present a low risk of dissolution in the water column, while heavy metals
such as Zn, Fe and Mn present from moderate to high risk. The S5 shows low risk for
Cu and Fe to be remobilized, but the risk for
Zn, Pb Cd, Fe, Mn and Ni is from moderate
to high. The S6 sample shows a low risk for
Cu, Pb, Cd, Fe and Ni and a higher risk for
Zn, Fe and Mn. The risk for Cu, Zn and Fe
in sample S7 is low, but there is a high risk
for Pb, Cd, Mn, Co and Ni to enter into the
human food chain through fish farming activities near Tiquina town. The samples S8
and S9 show a similar behavior, the risk for
Zn and Fe is low, while the other metals
show from moderate to high risk to be mobilized. Only Mn represents high and extreme risk because it ca be remobilized by
changes in environmental condition such as
pH and Eh.
In general, the RAC values show that Cu
and Fe represent from low to moderately
risk; moreover, Cd, Co, Mn, Ni, Pb, and Zn
indicate from moderate to high risk to hydrologic systems and thereafter entering into
the food chain (i.e. fish).
Geoaccumulation index, Igeo (Paper V)
The Igeo was calculated to determine metal
contamination in sediments of Lake Titicaca
by comparing the observed concentrations
with reference values for crustal sediments
(Fig. 27). Zinc has a particular distribution in
44
the studied sediments because it is enriched
due to mining activities as show in samples
S1, S4 and S5. All other sites are not considered polluted. Lead varies from non-polluted
to highly polluted, again sample S4 has a
higher value that reflects the impact of mining activities. For samples S1, S2, S3, S6 and
S9 the Igeo values indicate a moderate pollution that can be attributed to exploitation of
Pb, Zn, and Ag in polymetallic deposits.
Cadmium in samples S1, S5 and S6 has values that indicate from no pollution to moderate pollution, sample S3 shows moderate
contamination, samples S2, S7, S8 and S9
show moderate to high pollution, and finally
sample S4 is highly polluted which again
could be attributed to the mining activities.
Metal enrichment factor, EF (Paper V)
The EF values are higher than 1; the TEs
showing significant enrichment (5 – 20) are
Cu, Mn, Ni, and Zn, while Co varies between significant and very high enrichment
in the shallow sediments. Conversely, Cd, Pb
and Cd are extremely enriched in the sites
with mining activities; whereas in other sites
they are significantly enriched. Hence, the
values higher than 1 indicated that all TEs
measured in the sediments were enrichment
by various anthropogenic sources in the
basin area of Lake Titicaca. Hence, the RAC
evaluation shows from moderate to high risk
for mobilization and/or remobilization of
metals (Cu, Zn, Pb, Cd, Fe, Mn, Co and Ni)
from the bottom sediment to the aquatic
ecosystem. There are both similarities and
discrepancies between the Igeo and EF values, but both indicators show the enrichment of Zn, Pb and Cd in sediments. However, the discrepancies could be explained by
the variability of sediment sources, local
geology and the depth of the sediments and
also by different assumptions implemented
in each environmental indicator calculation.
According to the Risk Assessment Code
(RAC), there is a low to moderate risk for
Cu and Fe, while there is a moderate to high
risk related to Zn, Pb, Cd, Mn, Co, and Ni
remobilization to the water column. The
Igeo index indicates unpolluted status for
Cu, Mn, Co, and Ni; high pollution for Zn
and Pb, and finally extreme pollution for Cd.
Additionally, EF values suggest that Zn, Pb,
and Cd have extremely high enrichment in
the sediments in the point close to mining
activities (S4). Based on results of this study,
it is important to perform further studies to
determine possible bioaccumulation of
heavy metals in the fish fauna since fish is a
staple food of the local population.
8 C ONCLUSIONS
TEs study was conducted in three different
spatial units: Basin, Sub-basin and transect in
mining areas. The importance of the Poopó
Basin approach was to assess the distribution of As and other TEs around the basin,
but it was not possible identify the processes
associated with each region. However, some
processes were suggested on the basis of
field, lab investigation and modeling results.
The high concentrations of As and TEs are
not always associated with (mining) activities
in mining areas, these also can occur in areas
where there are no mining activities (southern side of Lake Poopó), highlighting that
the characteristics of each site play an important role in the mobilization and attenuation of TEs, including both biotic and abiotic processes.
The present study shows that the hydrochemistry of groundwater is controlled by
several processes; in the Antequera and Poopó sub-basins there is a dominant silicate
weathering; moreover, dissolution of carbonate minerals is more significant in the
Antequera than in the Poopó sub-basin.
Cation exchange is also partly responsible
for higher Na+ and K+ concentrations.
However the halite dissolution is a more
important process. In surface water, the
Gibbs diagram reveals that both rock weathering and evaporation-crystallization processes control water chemistry in the Antequera and Poopó samples. Moreover, the
data suggest predominance of silicate weathering in both sub-basins followed by dissolution of evaporates and carbonate weathering,
additionaly the oxidation of sulfide minerals
to some extents is also important in the
study area.
45
In both Antequera and Poopó sub-basins
factor analysis was applied and it was possible to identify five geochemical processes: i)
plagioclase weathering, ii) dissolution of
gypsum and halite, iii) TE mobilization at
acidic pH, iv) release of As following competition with phosphate and bicarbonate for
adsorption sites. Whereas for surface water
data suggests the dominance of the following processes: i) weathering and mobilization
of TEs influenced by pH, ii) dissolution of
evaporite salts, iii) neutralization of acid
mine drainage, iv) As release due to dissolution of Mn and Fe oxides, and v) sulfide
oxidation.
A detailed transect study in soils was used
for evaluating the pseudo total TE content
in soil, the data indicate that the geogenic
signal is strong suggesting that the background contents of these TEs are high.
However, in terms of bioavailable TEs concentrations in soils follow the order Cd>
Zn> Cu> Pb, and the distribution of bioavailable Cd and AR values suggest continuous soil enrichment. The DTPA method
extracted show less than 2% of the total As,
while the sequential methods reported up to
12% (< 2%, step 1 and < 10.0%, step 2),
which represents less than 3.1 mg/kg of the
total As content, as a potentially mobilized
fraction, which could be transferred to crops
or dissolved in groundwater. The large pool
of As can be accumulated in the soils due to
amorphous and crystalline Fe oxide surfaces
present in the soils, which was confirmed by
the fixed arsenic fraction (fractions 3, 4, and
5).
Furthermore, evaluation of the edible part of
the crops showed that As and Cd concentrations in the edible part of the crops (beans,
barley and potato) are lower than the limits
of FAO, WHO, EC, and Chilean international regulations. In contrast, Pb shows
high concentrations for beans and potato by
~ two fold, but not for barley.
The understanding of the TE in lake sediments and their mobilization to the water
column was improved by the sequential extraction method. The BCR method was used
to evaluate the distribution of TEs in four
sediment fractions, the exchangeable, reducible, oxidizable and residual fractions. The
TE concentrations in the fractions agree
with the information on chemical processes
that can explain the adsorption and mobilization of TEs in lake sediments.
9 F UTURE WORK
In future work, it is important to understand
the processes that govern the dissolution of
arsenic as a function of the water level
through piezometer installation. Moreover
sequential extractions for As in soils and
sediments may be modified to consider the
salinity of the groundwater (due to i.e. the
dissolution of halite).
It is also important to consider the speciation of TEs (especially organic-As and inorganic-As) in crops and their bioaccessibility
for the human body, linked to WHO/FAO
provisional tolerable weekly intake (PTWI).
TEs should be further explored in mining
areas of the Bolivian Altiplano for minimizing the potential health risks.
Future research based on the WHO/FAO
provisional tolerable weekly intake (PTWI)
of trace metals is needed in the study areas
of the Bolivian Altiplano affected by mining
to minimize the potential health risks from
TE contamination in the food chain.
46
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Zheng R, Li H, Jiang R, Römheld V, Zhang F, Zhao F. 2011. The role of roots hairs in cadmium
acquisitions by barley. Environmental Pollution. 159:408-415.
Other publications
La Patria newspaper, 2010a. Increasing prices, royalties and usefulness, Perspectiva Minera.
La Patria newspaper, 2010b. Increasing the activities in the national mining companies. Perspectiva Minera.
CIDSE, 2009. Impacts of extractive industries in Latin America. URL:http//www.cidse.org.
Perales V. H. 2010, Conflictos geolopoliticos por el agua en las cuencas mineras del Departamento de Oruro, Bolivia. VertigO, serie 7. URL:http//www.vertigo.revues.org/9769.
Ministerio Metalurgia y Mineria. (MMM), 2013. (URL: http://www.mineria.gob.bo/Documentos/Estadisticas/Exportaciones.pdf (visit date: 2013-04-15).
Instituto nacional de estadística (INE). URL: www.ine.gob.bo (visit date 2014-03-20).
El Diario newspaper, 2012. Bolivia: de los barones del estaño a los dueños de la minería. URL:
http://eju.tv/2012/06/bolivia-de-los-barones-del-estaño-a-los-dueños-de-la-minera/
(visit
date: 2014-03-20).
DIMA-COMIBOL, 2014. Mining propierties map. (URL: http://dimacomibol.gob.bo/en/donde_operamos/mapa_geografico. (visit date: 2014-04-28).
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