Vindicating the Impact of Heavy Metal Residues in Spinach Through

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Vindicating the Impact of Heavy Metal Residues in Spinach
Through Household chemicals
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4
Rai Muhammad Amir1*, Faqir Muhammad Anjum1, Muhammad Atif Randhawa1,
Muhammad Sarwar2
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*
1
National Institute of Food Science and Technology, University of Agriculture, Faisalabad,
Pakistan
Institute of Animal Nutrition and Feed Technology, University of Agriculture, Faisalabad,
Pakistan
For correspondence: [email protected]
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Abstract
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Heavy metals are major category of globally distributed pollutants and natural elements that have
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been extracted from earth and harnessed for human industry and products. Food production and
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its safety is the major issue around the world. Metals are notable for their wide environmental
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dispersion from such activity, their tendency to accumulate in selective tissues of the human
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body and their overall potential to be toxic even at relatively minor levels of exposure. The
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intake of heavy metals through diet leads to several disorders such as kidney damage, nervous
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disorder, bone disease and tubular growth. The present study was conducted to mitigate the
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residues of heavy metals Pb, As, Zn and Hg in spinach collected from self-grown supervised
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field by using different washing techniques. The amount of trace metals were measured in fresh
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and chemically washed spinach samples with the help of Atomic Absorption Spectrophotometer
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(AAS). The results obtained in recent study indicated heavy metal residues reduced drastically
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when spinach samples were subjected to washing treatment irrespective to type of washing
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declined the mercury residues varying from 7 to 23 %, lead 7 to 28 %, zinc 15 to 54 % and
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arsenic 6 to 22%. More reduction was found in zinc followed lead, mercury and arsenic,
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respectively.
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Keywords: Heavy metals, Spinach, Wastewater, Washing Treatments
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Introduction
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Pakistan is an agricultural country sanctified with plenteous natural possessions like productive
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soil, irrigation water and miscellany of climate ranging from tropical to temperate. The use of
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sewage water for agricultural purpose has tremendously increased during last few years due to
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shortage of water availability, especially in semiarid region of Pakistan. The vegetables plays an
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important role for the protection of health and prevention of various ailments, repair the organ of
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body, maintaining alkaline reserve of the body and possess high carbohydrate, vitamins and
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minerals contents (1).
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The contamination of heavy metals mostly occurs due the application of fertilizers, waste water
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irrigation, use of metal-based pesticides, industrial emissions and transportation on crops (2).
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The contamination of soil is becoming environmental problem in Pakistan due to increasing
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heavy metals (3). The wastewater irrigation is the major contributor of heavy metal contents to
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the soil and ultimately vegetables becoming a very serious issue in Pakistan because these
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effluents are heavily loaded with harmful metals and metallic compounds (4, 5, 6, 7). The
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traditional washing methods are used to get rid of waste and filth prior to use vegetables because
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these are considered significant for the reduction of residues of heavy metals. A series of
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washing solutions such as ozonated water, bleach solution and strong acid has been found
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successful in removing heavy metals, pesticides and chemical residues. The vegetable samples
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washing with tap water for 2–3 times result the reduction of residues of heavy metals drastically
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and the contaminated load was eliminated best for lead and cadmium from 75–100% than those
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for copper and zinc 27– 55% (8).
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The residues of heavy metal and other particles deposited on the surface of vegetables removes
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significantly by simple washing (9). In spinach, heavy metal reduction was found 21%, 21%,
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13% and 26% for Pb, Cd, Cr and Zn respectively but almost unaffected for Ni in unwashed and
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washed samples. In coriander the concentration of Cd, Pb, Cr, Ni and Zn reduced by 11%, 31%,
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11%, 5% and 6% and for methi reduction pattern 14%, 13%, 15%, 17% and 13% for unwashed
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and washed samples, respectively (10).
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The increasing concentration of heavy metal residues in water, soil and foodstuff is an alarming
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phenomenon around the world. The pollution of water and soil directly linked with cross
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contamination of food chain through irrigation. The United States and European Union has
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already set up strict limits for most of the heavy metals in water but current food legislation does
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not have legal limits for a number of heavy metals in food and this fact causes considerable
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health hazards to babies, children, pregnant women and all other consumers. Keeping in view the
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persistent nature and cumulative behavior as well potential toxic effects of heavy metal residues
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as a result of consumption of vegetables, the present study has been designed to determine the
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heavy metals in spinach to explore the efficiency of chemical and biological solutions to reduce
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the residues of heavy metals.
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Materials and Methods
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Vegetable sample collection
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The samples of spinach were collected from self grown, supervised field. One kg sample of
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spinach was obtained at the point of optimum maturity. The samples were instantly shifted to the
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laboratory of National Institute of Food Science and Technology, for subsequent analysis of
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samples.
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Sample Preparation
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The collected vegetable samples were reduced to appropriate size by using knife to facilitate the
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analysis. The study was designed with different washing treatments by using tap water
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and following concentrations of chemical solutions in water along with one unwashed sample.
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Table 1: Different Washing Treatments
Reagents
Unwashed
Tap water
Reddish extract
Sodium Carbonate
Hydrogen Peroxide
Lemon extract
Citric Acid
Concentrations
Washing Treatments
5%
10%
5%
10%
5%
10%
5%
10%
5%
10%
Treatments
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
6
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After solution preparation vegetable sample were soaked in solution for ten minutes for washing
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purpose. The washed vegetable was blended by using commercial blender to make
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homogeneous paste of pulp and juice. The vegetable samples (three replicates of each
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washing treatment) were kept in hot air oven at 70 -80oC till complete dryness. The dried
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vegetable samples of different parts of vegetables were ground into a fine powder (80 mesh)
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using a commercial blender and stored in polyethylene bags for analysis.
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Sample Digestion
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The powdered vegetable sample (0.5-1.0 g) was taken into a Pyrex beaker; 10 ml of concentrated
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HNO3 was added to it and kept overnight without heating. It was then heated on a hotplate and
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after evaporation near to dryness, the sample was cooled and 5 ml HClO4 was added and heated
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again. After digestion was complete, the sample was filtered into a clean volumetric flask and
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diluted to 50 ml with double de -ionized water (11).
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Preparation of Standards
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The standard solutions (5, 10, 15 and 20 ppm) of all the metals (Hg, Pb Zn and As) were
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prepared from the stock standard solutions containing 1000 ppm in distilled water.
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Determination of Metals
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The heavy metals Hg, Pb Zn and As in unwashed, tape water, chemically washed, dried
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and digested vegetable samples was determined by using Varian GTA 120 AA 240
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Graphite Atomic Absorption Spectrophotometer (12). The data obtained was analyzed and
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represented using standard statistical procedures i.e. completely randomized design (CRD) as
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described by (13)
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Results
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The concentrations of mercury, lead, zinc and arsenic were analyzed in different samples of
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spinach collected from supervised field at the stage of optimum maturity. The results regarding
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these heavy metals concentration in spinach showed significant variation and linear reduction of
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heavy metals as presented in Table 2, 3, 4 and 5, respectively. The concentrations of heavy
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metals in unwashed spinach samples were higher than samples subjected to different washing
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treatments. The result regarding mercury showed progressive increase in reduction of residues of
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mercury with the increase of concentration of treatments (Table 2). Out of all the washing
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treatments, it was observed that the minimum reduction of mercury residues 7% was recorded
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whenT1 i.e. tap was applied to spinach. The spinach treated with T12 i.e 10% citric acid yielded
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the maximum reduction of mercury which was 23% followed by lemon extract 22%, sodium
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carbonate 17%, reddish extract 15% and hydrogen peroxide 12%. Furthermore, the maximum
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reduction of lead residues 28% was observed when T12 i.e. 10% citric acid was applied to
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spinach (Table3). Similarly unwashed samples of spinach were found to be heavily contaminated
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with zinc and arsenic. The tap water reduces the lead, zinc and arsenic contents by 7, 15 and 6%
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in spinach and T12 i.e. 10% citric acid was found to be more effective in all the spinach samples
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to reduce lead, zinc and arsenic contents as shown in the Table 3, 4 and 5.
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Table 2: Mean±S.D value and percent reduction of mercury in spinach
Treatments
T1 Unwashed
T2 Tap water washed
T3 Reddish extract 5 %
T4 Reddish extract 10 %
T5 Sodium Carbonate 5 %
T6 Sodium Carbonate 10 %
T7 Hydrogen Peroxide 5%
T8 Hydrogen Peroxide 10%
T9 Lemon extract 5 %
T10 Lemon extract 10 %
T11 Citric Acid 5 %
T12 Citric Acid 10 %
Vegetable
Spinach
Mean+S.D mg/kg
0.0481±0.00081a
0.0447±0.0023b
0.0436±0.0016bc
0.0408±0.0007de
0.0429±0.0013bcd
0.0399±0.0008ef
0.0446±0.0013b
0.0422±0.0005cd
0.0429±0.0017bcd
0.0374±0.0019f
0.0410±0.0016de
0.0370±0.0017f
Percent Reduction (%)
7
9
15
11
17
7
12
11
22
15
23
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Table 3: Mean±S.D value and percent reduction of lead in spinach
Treatments
T1 Unwashed
T2 Tap water washed
T3 Reddish extract 5 %
T4 Reddish extract 10 %
T5 Sodium Carbonate 5 %
T6 Sodium Carbonate 10 %
T7 Hydrogen Peroxide 5%
T8 Hydrogen Peroxide 10%
T9 Lemon extract 5 %
T10 Lemon extract 10 %
Vegetable
Spinach
Mean+S.D mg/kg
0.9838±0.0055a
0.9127±0.0017b
0.8638±0.0039d
0.8034±0.0029i
0.8541±0.0043e
0.8235±0.0032g
0.9035±0.0037c
0.8548±0.0012e
0.8340±0.0038f
0.7267±0.0029j
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Percent Reduction (%)
7
12
18
13
16
8
13
15
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T11 Citric Acid 5 %
T12 Citric Acid 10 %
0.8121±0.0105h
0.7067±0.0032k
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28
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Table 4: Mean±S.D value and percent reduction of zinc in spinach
Treatments
T1 Unwashed
T2 Tap water washed
T3 Reddish extract 5 %
T4 Reddish extract 10 %
T5 Sodium Carbonate 5 %
T6 Sodium Carbonate 10 %
T7 Hydrogen Peroxide 5%
T8 Hydrogen Peroxide 10%
T9 Lemon extract 5 %
T10 Lemon extract 10 %
T11 Citric Acid 5 %
T12 Citric Acid 10 %
Vegetable
Spinach
Mean+S.D mg/kg
7.4747±0.0227a
6.3577±0.0220b
5.8498±0.0164d
5.0962±0.0992ef
5.9077±0.0099cd
4.4114±0.3785h
6.0669±0.0296c
5.0091±0.0003fg
5.2344±0.0181e
3.5816±0.0362i
4.8476±0.0811g
3.4316±0.0274i
Percent Reduction (%)
15
22
32
21
41
19
33
30
52
35
54
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Table 5: Mean±S.D value and percent reduction of arsenic in spinach
Treatments
T1 Unwashed
T2 Tap water washed
T3 Reddish extract 5 %
T4 Reddish extract 10 %
T5 Sodium Carbonate 5 %
T6 Sodium Carbonate 10%
T7 Hydrogen Peroxide 5%
T8 Hydrogen Peroxide10%
T9 Lemon extract 5 %
T10 Lemon extract 10 %
T11 Citric Acid 5 %
T12 Citric Acid 10 %
Vegetable
Spinach
Mean+S.D mg/kg
0.1048±0.0105a
0.0987±0.0013b
0.0965±0.0006bcd
0.0913±0.0007def
0.0976±0.0005bc
0.0928±0.0005cdef
0.0976±0.0014bc
0.0945±0.0015bcde
0.0943±0.0006bcde
0.0889±0.0008f
0.0903±0.0009ef
0.0818±0.0011g
5
6
7
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Percent Reduction (%)
6
8
13
7
11
7
10
10
15
14
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Discussion
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The results pertaining from the present study that the heavy metal residues reduced drastically
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when spinach samples were subjected to washing treatment irrespective to type of washing,
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different treatments declined the mercury residues varying from 7 to 23 %, lead 7 to 28 %, zinc
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15 to 54 % and arsenic 6 to 22% in spinach. More reduction was found in zinc followed by lead,
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mercury and arsenic, respectively. Zinc showed more reduction due to their physiochemical
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properties and more dissolving power as compared to other heavy metals. The variation in
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reduction of heavy metal residues during washing operation may be due to differences in the
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behavior and nature of chemicals using in washing treatments. The washing of spinach with tap
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water removes most of the heavy metal residues adhered to the surface of the spinach as well as
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in the skin of the vegetable due to its dissolving power because that is considered a universal
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solvent. The present study results also indicated that citric acid showed maximum reduction of
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heavy metal residues due its working ability as a chelating agent and resulting made the heavy
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metal residues unavailable, salt solution sodium carbonate also reduced significant amount of
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heavy metal residues and biological extract lemon showed more reduction of heavy metal
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residues as compared to reddish extract. The acidic detergent solution was more effective in the
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elimination of the zinc, lead, mercury and arsenic under investigation than salt solution and
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biological extracts. The vegetables play vital role in maintaining the nutritional status of humans.
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The accumulation of heavy metals in vegetables uptake from soil, water and atmosphere.
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The intake of heavy metals through diet leads to several disorders such as kidney damage,
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nervous disorder, bone disease and tubular growth. The uptake of metals in vegetables from
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contaminated soil by absorbing them as well as from deposits on the vegetable parts exposed to
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the air from polluted environments.
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The results of the present study are in conformity with the previous findings of (14) who found
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that the residues of different heavy metals lead and cadmium were declined considerably during
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washing of vegetables. The results of the present studies are also fairly in agreement with the
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findings of (8). All vegetable samples were found to be heavily contaminated with different
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metals. The excessive intake of toxic metals can cause severe complications in humans and
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animals. There are already published works related to the incidence of cancer of the pancreas,
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urinary bladder or prostate and gastrointestinal cancer (15). Lead, mercury and chromium were
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found to be accumulated in the shoot and roots of plants at low, medium or high levels (16). The
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leafy vegetables have the tendency to uptake toxic metals more as compare to other vegetables
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because of their more exposure to environmental pollution (17) also reported that leafy
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vegetables were more contaminated with cadmium (0.09μgg-1) and the minimum concentration
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(0.002μgg-1) was in cucurbit vegetables (Indian squash). Results also showed that maximum
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concentration (0.15μgg-1) of lead was found in leafy vegetables (coriander) and the minimum
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concentration (0.001μgg-1) in root/ tuberous vegetables (sugar beet). The results of the current
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study are very close to the achievement of (18) who estimated the concentration of cadmium in
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unwashed vegetables. The cadmium reduction pattern in this study was parallel to the
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investigation that was carried out by (8) to estimate the heavy metal load of unwashed and
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washed vegetables in peri-urban, Delhi. In addition, (10) also reported the same reduction pattern
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of cadmium in spinach, okra and brinjal, exposed to different degrees of pollution in Agra, by
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washing with tape water. The arsenic is a toxic element and the humans may get exposure to
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arsenic through drinking water obtained by wells bored into arsenic contaminated areas or
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through contaminated water by agro-chemical waste or industrial effluents. (19) also reported the
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arsenic reduction by washing of vegetable with tape water but that was slightly high than in
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present study.
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The level of lead is higher than the recommended (0.2 μgg-1) in humans, cause bones,
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pancreases, gum, liver, nervous system, teeth and blood diseases. Lead toxicity results in
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reduction of hemoglobin synthesis, joints pain, kidney damage, defects in reproductive,
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cardiovascular and nervous systems. The results of the present study regarding the lead
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concentration in unwashed vegetables are the same as described by (20) to estimate
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concentration of different heavy metals in vegetables. Lead reduction by tap water washing
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follows the same pattern as reported by the (8) to estimate the heavy metal load of unwashed and
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washed vegetables in peri urban, Delhi. In past, higher level (0.02μgg-1) of mercury was found in
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fenugreek/methi i.e. leafy vegetables and the lower contents (0.001μgg-1) were found in
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root/tuberous vegetables and fruity vegetables (okra) was found to be heavily contaminated
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with arsenic (0.083 μgg-1) whereas the minimum level (0.014μgg-1) was detected in cauliflower
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(21).
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Conclusions
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The spinach samples were contaminated with different residues of heavy metals. Wastewater
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irrigation is the single largest and main source of heavy metals contamination in soil as well as in
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vegetables. The spinach shows higher accumulation of different metals because of its large
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surface area and the washing of spinach with tap water and household chemical solutions not
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only remove the dirt and dust particles but also reduced the heavy metals significantly. The
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washing treatments mechanically remove the heavy metals deposited on the surface of
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the vegetables. On the basis of present study, it is strongly recommended that vegetables must
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not be grown with sewerage water and at household level the vegetables must be washed with
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tap water as well as washing treatments like citric acids, hydrogen peroxide, sodium carbonate
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and biological extracts lemon and radish in order to reduce the residues of heavy metals. These
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methods are very simple because they can easily perform at local conditions and beneficial due
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their working ability to mitigate the metal residues.
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Conflict of Interest
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The authors declare that there is no conflict of interests regarding the publication of this paper.
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