Determination and comparison of uranium and radium isotopes

Journal of
Environmental Radioactivity 57 (2001) 175–189
Determination and comparison of uranium and
radium isotopes activities and activity ratios in
samples from some natural water sources in
Morocco
O.K. Hakama,c,*, A. Choukria, J.L. Reyssb, M. Lferdec
a
Laboratoire des Faibles Radioactivite´s et de l’Environnement, Faculte´ des Sciences,
De´partement de Physique, Universite´ Ibn Tofail, 14 000, Ke´nitra, Morocco
b
Laboratoire des Sciences de climat et de l’Environnement, Laboratoire Mixte CNRS-CEA, 91 198,
Domaine du CNRS, Avenue de la Terrasse, Gif sur Yvette cedex, France
c
Laboratoire de Physique Nucle´aire, Faculte´ des Sciences, De´partement de Physique,
Universite´ Mohammed V, Avenue Ibn Battouta B.P. 1014, Rabat, Morocco
Received 1 October 1999; received in revised form 20 December 2000; accepted 5 January 2001
Abstract
Radiochemical results (238U, 226Ra and 228Ra activities; 234U/238U, 228Ra/226Ra and
Ra/238U activity ratios) are reported for 42 natural water samples collected from wells, hot
mineral springs, rivers, tap water, lakes and irrigation water in 15 Moroccan locations. Results
show that 238U activity varies between 4.5 and about 309 mBq l 1 in wells, 0.6 and 8.5 mBq l 1
in hot springs, 9.7 and 28 mBq l 1 in rivers, 2.5 and 16 mBq l 1 in tap waters and between 6
and 24 mBq l 1 in lakes. The 234U/238U activity ratio varies in the range 0.87–3.35 in all
analyzed water samples except for hot springs where it reaches values higher than 7. Unlike
well water, mineral water samples present low 238U activities and high 234U/238U activity ratios
and 226Ra activities. The highest activity of radium in mineral water is 150 times higher than
the highest activity of 226Ra found in well water. 226Ra/238U activity ratios are in the ranges
0.07–1.14 in wells, 0.04–0.38 in rivers, 0.04–2.48 in lakes, and 1.79–2115 in springs. The
calculated equivalent doses to all the measured activities are inferior to the maximum
contaminant levels recommended by the International Commission of Radioprotection and
226
*Correspondence address: Laboratoire des Faibles Radioactivite´s et de l’Environnement, Faculte´ des
Sciences, De´partement de Physique, Universite´ Ibn Tofail, 14 000, Ke´nitra, Morocco. Tel.: +212-3-37361621; fax: +212-3-37-372770.
E-mail addresses: [email protected] (O.K. Hakam), [email protected] (A. Choukri).
0265-931X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 6 5 - 9 3 1 X ( 0 1 ) 0 0 0 1 6 - 9
176
O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
they do not present any risk for public health in Morocco. # 2001 Elsevier Science Ltd. All
rights reserved.
1. Introduction
Environmental pollution and management of water is a national and international
priority today. Climatic variations, population growth and industrial development
are responsible for the considerable growth in water needs. Therefore, it is necessary
to manage and protect the natural surface and underground waters.
The presence and behaviour of radioelements in natural waters from different
sources have been widely studied throughout the world (Andrews & Kay, 1983;
Asikainen, 1981; Asikainen & Kahols, 1979; Cherdyntsev, 1971; Ivanovich &
Harmon, 1982; Ivanovich & Harmon, 1992; Mangini, Sonntag, Bertsch, & Muller,
1979; Moore, 1967; Moore & Told, 1993; Hussain & Krishnaswami, 1980; Cowart &
Osmond, 1977; Michel & Moore, 1981; Palmer & Edmond, 1993). The behaviour of
uranium and thorium decay series nuclides in groundwater is of interest to
geochemists, uranium explorations, and health physicists. Studies of 238U series
nuclides in groundwater have had a variety of purposes including the calculation of
metal scavenging rates (Hussain & Krishnaswami, 1980) developing uranium
exploration models (Cherdyntsev, 1971), and the assessment of the effects of
phosphate mining on water quality (Kaufman & Bliss, 1977; Strain, Waston, &
Fong, 1979). On the other hand, 226Ra has been used as a tracer of large-scale ocean
circulation processes and observed increase of 226Ra with depth in the ocean reflects
the effects of biological cycling in the ocean surface together with the bottom source
function (Ku & Luo, 1994). Other studies concerning radium concentration in
riverine (Kraemer & Curwich, 1991; Key, Stallard, Moore, & Sarmiento, 1985) and
estuarine environments (Martinez-Aguirre, Garcia-Leon, & Ivanovitch, 1994) allow
one to understand the radium redistribution in the environment and the resulting
health consequences.
High concentrations of natural radioactive elements have been found in some
sources of natural water (Asikainen & Kahols, 1979; Cowart & Osmond, 1977;
Mangini et al., 1979; Moore, 1967). Samples of river water in mining areas or near
industrial installations could be polluted by toxic chemical or radioactive elements.
The natural polluting radioelements could rise from industrial wastes, geological
erosion of uranium-bearing rocks or excessive utilization of agricultural fertilizers.
Concentration of natural radioelements in water could be related to the physicochemical conditions and to the geological, geographical and socio-economical
environment. Uranium and thorium isotopes are generally measured by alpha
spectrometry, whereas radium isotopes are measured by gamma spectrometry.
In this work, we have applied for the first time in Morocco, a rapid combined
technique for measuring uranium and radium isotopes from the same water sample.
Some results obtained from natural water samples collected from different sites
(mineral springs, rivers, lakes, wells and tap water) will allow us to compare uranium
O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
177
and radium concentrations in these sites and help us to orient the next samplings in
order to establish a general distribution map of the radioelements in natural waters
of Morocco. A comparison between activities of uranium and radium isotopes in
natural water samples taken from different localities in Morocco could also help us
to know whether radioactivity had a polluting or natural origin. The knowledge of
uranium and radium concentrations in drinking water is important because an
appreciable fraction of the absorbed uranium and radium is deposited in bone, with
the corresponding contribution to the internal dose (UNSCEAR, 1993).
2. Sampling and methods
2.1. Area of investigation
The analyzed natural water samples have been collected from 15 wells, eight
mineral springs, eight rivers and three lakes. Tap water samples from six distant
cities and two irrigation water samples have been analyzed as well. The sampled sites
have been chosen at some locations in Morocco (Fig. 1) in order to give significant
Fig. 1. Map showing localities of the analyzed natural water samples.
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O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
preliminary results which could orient next samplings. The region of Fez is
characterized by the presence of hot mineral springs. Water of some of these sources
is commercialized in bottles (Sidi Harazem) or used as water of bath to heal some
skin sicknesses because of its wealth in mineral salts (Aı¨n Allah, My Yacoub).
Khouribga region is located in the interior of the country on the largest tray of
phosphates in Morocco. It is often affected by dryness, which explains the high
number of drilled wells in this region. Sample 10 has been taken from a well located
at about 1 km from one of the phosphates extraction site to the east of the city of
Khouribga. The Tamraght river, located to the west of the mountainous chain of the
High Atlas to the north of the city of Agadir, goes directly from the mountain to the
sea. The Sebou river passes beside several factories that probably contribute to the
water pollution by industrial wastes. Some tributaries of the Oum Rbiaˆ river cross
regions situated on the Khouribga tray of phosphates. The other rivers crossagricultural regions where the use of fertilizers, often rich in uranium, may
contribute to a radioactive pollution of these waters. In case of pollution of the
analyzed water, the radioactive analysis of these waters will allow us to evaluate the
radioactive pollution as a function of the geological context and the socioeconomical environment of the sampled sites.
2.2. Sample preparation
Twenty litres of water are collected in a polyethylene tank and immediately
acidified slightly to pH 2–3 with concentrated HNO3. After filtration, iron carrier
(FeCl3) (60–80 mg) and known 232U–228Th equilibrated spike solution are added.
Uranium and thorium are coprecipitated with Fe(OH)3 by addition of NH4OH at
pH 8–9 as described by Choukri (1994) and a known quantity of barium in BaCl2
form is then added. Radium isotopes are coprecipitated with BaSO4 formed by
addition of sulphuric acid drops in the medium without a significant change in pH.
Precipitation of hydroxides is achieved before barium and sulphuric acid addition
step to avoid coprecipitation of thorium with BaSO4. The two precipitates are
recovered by filtration.
Hydroxides containing uranium and thorium are soluble in acid medium, whereas
BaSO4 precipitated with radium is not soluble in this medium. The two fractions are
separated by filtration or centrifugation.
2.3. Separation and activity measurement of uranium and thorium isotopes
Complete mixing and oxidation are achieved by evaporating the solution to
dryness. The dry residue is dissolved in 8 N HCl and the hydroxides are precipitated
at pH 8–9 with ammonium hydroxide. In this step, thorium and uranium are
precipitated together with iron hydroxides, aluminium and other impurities. After
dissolution in 8 N HCl, the sample is filtered and is ready for the ion exchange.
A single resin exchange column is used twice:
1. In the first step, uranium and iron are fixed on the resin in an 8 N HCl medium
while thorium and other impurities are collected with the effluent. Fe is then
O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
179
Fig. 2. Separation scheme for uranium and thorium by ion-exchange resin.
eluted with 15 ml of 8 N HNO3. Uranium is eluted with 30 ml of 0.1 N HCl and
evaporated to dryness.
2. In the second step, thorium is loaded on the resin bed in 30–40 ml of HNO3 to
ensure its fixation solely. Then thorium is eluted with 8 N HCl and evaporated to
dryness. The ion-exchange procedure is shown in Fig. 2. It is identical to that used
for uranium and thorium separation in carbonate samples with minor
modifications (Ku, 1965; Choukri, Reyss, Turpin, & Berrada, 1994).
After these anionic exchange steps, thorium is ready for deposition while uranium
must be separated from residual iron. Its purification is performed by di-isopropyl
ether extraction, followed by evaporation of the aqueous fraction containing
uranium.
In the last step, uranium and thorium are extracted separately with TTA (1-(2thenoyl)-3,3,3-trifluoroacetone) in toluene in a nitric media at pH 3 and 1,
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O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
respectively. The two organic phases containing uranium and thorium are
evaporated onto aluminium foils and flamed to remove any trace of carbon. The
thin sources are, at the end, ready for alpha spectrometry.
2.4. Measurement of radium
Radium is extracted from the water samples by precipitation with BaSO4 after
removal of uranium and thorium as described above. Schmidt and Reyss (1996)
reported that this method is essentially quantitative for radium removal. The
(Ba(Ra)SO4) is dried at room temperature. The obtained powder is sealed into a
plastic ferrure whose form is compatible with the dimensions of the well-used
Germanium detector. The gamma spectrum is measured after 20 days which is
necessary to ensure radioactive equilibrium between radium isotopes and their
daughters used to determine the activities of the firsts. The efficiency of radium
extraction by BaSO4 precipitation is obtained by calculating the weight of recovered
BaSO4 to the introduced BaCl2 (corrected by a mass factor of 1.16). Extraction
efficiencies are, in most cases, in the range of 75–100%. Radium isotope activities are
measured by gamma spectrometry using a 220 cm3 low-background well type gamma
ray detector in the Laboratoire Souterrain de Modane (LSM-Centre National de la
Recherche Scientifique (CNRS/CEA, France).
3. Results and discussion
The uranium isotopes (234U, 238U), Ra isotopes (226Ra, 228Ra) activities and the
U/238U, 228Ra/226Ra and 226Ra/238U activity ratios for the all samples are given in
Table 1. The 238U and 226Ra activities covered wide ranges, from 0.6 mBq l 1
measured in Oulmes mineral water sample to about 310 mBq l 1 in the well water
sample located at about 1 km from phosphates extraction site in Khouribga area for
238
U and from 0.46 mBq l 1 in Kenitra tap water sample to 3696 mBq l 1 in the My
Yacoub mineral water sample for 226Ra. The 234U/238U, 228Ra/226Ra and 226Ra/238U
covered also wide ranges (Table 1). The errors quoted in Table 1 are one sigma
uncertainties due to counting statistics.
234
3.1. Wells
Among the analyzed well water samples, samples 1 and 5 presented the lowest
activity of 238U, samples 4 and 10 presented the highest activities. The mean activity
of 238U in wells was about 66 mBq l 1. The 226Ra activity measured for seven well
water samples ranged from 1 to 25 mBq l 1 with a mean value of 9.8 mBq l 1. The
226
Ra/238U activity ratio varied between 0.07 and 1.14.
Except in samples 1 and 4 where 228Ra/226Ra is >1, the activities of 228Ra
originating from 232Th were lower than those of 226Ra originating from 238U. The
228
Ra/226Ra ratio is more variable than 234U/238U because their origins are in
Table 1
Activities of uranium and radium radioisotopes (238U, 226Ra,228Ra) and activity ratios (234U/238U, 226Ra/228U, 228Ra/226Ra) in analyzed natural water samples
Sample
Locality
238
U (mBq l 1)
234
U/238U
226
Ra (mBq l 1)
228
Ra (mBq l 1)
228
Ra/226Ra
226
Ra/238U
6.3 0.5
61 4
45 4
165 27
4.5 0.3
23 2
26 2
64 8
63 5
309 28
64 7
55 5
17 2
57 5
34 3
2.11 0.13
1.01 0.02
0.97 0.03
1.01 0.04
1.98 0.12
1.08 0.05
1.16 0.04
0.80 0.06
0.88 0.04
0.79 0.02
2.64 0.21
2.26 0.11
1.45 0.11
2.83 0.12
2.08 0.12
1.0 0.2
6.3 0.3
5.4 0.4
10.8 0.5
5.1 0.3
25 1
15.1 1.4
}
}
}
}
}
}
}
}
1.2 0.3
4.8 0.5
4.9 0.6
17.3 1.3
1.0 0.2
51
0.6 0.4
}
}
}
}
}
}
}
}
1.20 0.38
0.76 0.09
0.90 0.13
1.59 0.14
0.20 0.04
0.20 0.04
0.04 0.03
}
}
}
}
}
}
}
}
0.16 0.03
0.104 0.008
0.12 0.01
0.07 0.01
1.14 0.10
1.11 0.10
0.58 0.07
}
}
}
}
}
}
}
}
Mineral springs
16
Sidi Harazema (s)
17
Sidi Harazemb (s)
18
Sidi Harazem (c)
19
Aı¨n Allaha (s)
20
Aı¨n Allahb (s)
21
My Yacoub (s)
22
Oulmes (c)
23
Sidi Ali (c)
Fez
Fez
Fez
Fez
Fez
Fez
Oulmes
Oulmes
6.1 0.7
5.2 0.6
5.2 0.5
5.4 0.6
8.5 1.1
6.5 0.8
0.6 0.1
5.1 0.8
6.45 0.53
7.39 0.62
6.94 0.56
4.76 0.32
3.13 0.26
1.84 0.25
4.13 0.74
0.97 0.15
51.9 1.3
60.4 1.6
89.1 1.2
30.0 0.6
26.8 0.6
3696 12
1248 3
9.1 0.6
9.1 1.1
11.4 1.4
16.2 1.1
3.1 0.1
2.4 0.4
620 10
67 2
3.3 0.6
0.18 0.02
0.19 0.02
0.18 0.01
0.100 0.004
0.09 0.01
0.168 0.003
0.053 0.001
0.36 0.01
8.58 1.04
11.59 1.39
17.17 1.73
5.56 0.61
3.15 0.39
573 66
2115 321
1.79 0.29
Rivers
24
Tamraght
25
Sebou
26
Fouarat
Agadir
Kenitra
Kenitra
12.66 0.07
13.3 1.7
11.5 0.7
2.14 0.07
1.38 0.12
1.07 0.05
0.8 0.1
2.3 0.1
1.12 0.14
1.6 0.3
2.9 0.2
0.78 0.05
1.95 0.44
1.25 0.05
0.70 0.09
0.07 0.01
0.17 0.02
0.10 0.01
181
Beni Mellal
F.B. Salah
F.B. Salah
Settat
Khouribga
Khouribga
Khouribga
Khouribga
Khouribga
Khouribga
Erfoud
Rissani
Tiflet
Tiflet
Errachidia
O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
Wells
1
Beni Mellal
2
Ouled Reguia
3
Beni Amir
4
Settat
5
Beni Yakhlef
6
Ourghida
7
Lahmina
8
ouled essassi
9
ouled Azouz
10
1 km from phos. Extrac. site
11
Erfoud
12
Rissani
13
Jorf Melha
14
Tiflet
15
Zrigate
182
Table 1 (continued)
238
234
Oum Rabiaˆ
Oum Rabiaˆ
Nfifikh
Bouregreg
Tiflet
Settat
Kasbat Tadla
Casablanca
Sale
Tiflet
9.7 0.8
14.1 1.5
28 3
24.2 2.3
27.2 2.3
1.55 0.09
1.54 0.16
1.84 0.09
1.28 0.10
2.49 0.15
1.71 0.07
5.3 0.3
1.2 0.1
}
}
1.71 0.15
2.7 0.4
1.7 0.2
}
}
1.00 0.09
0.51 0.08
1.37 0.21
}
}
0.18 0.02
0.38 0.05
0.044 0.005
}
}
water
Kenitra
Khouribga
Errachidia
Beni Mellal
Kasbat Tadla
F.B. Salah
Kenitra
khouribga
Errachidia
Beni Mellal
Kasbat Tadla
F.B. Salah
2.5 0.3
15.7 1.4
10.2 1.4
8.3 1.2
7.2 0.6
13 1
1.14 0.21
1.38 0.07
3.35 0.41
1.54 0.24
2.08 0.12
1.91 0.08
0.46 0.06
35 2
}
2.1 0.3
41 2
46 1
0.77 0.04
7.7 1.4
5 0.4
5.4 2.2
12 1
1.67 0.23
0.22 0.04
0.13 0.05
0.27 0.02
0.18 0.03
2.20 0.22
5.61 0.49
3.54 0.28
Lakes
38
Fouarat
39
Boughaba
40
Beni Yakhlef
Kenitra
Mehdia
Khouribga
6.00 0.05
23.7 6.5
9.3 1.1
0.87 0.09
1.11 0.17
1.16 0.10
0.81 0.05
0.92 0.08
23 3
0.61 0.01
0.70 0.01
11 3
0.75 0.05
0.76 0.07
0.48 0.14
0.140 0.009
0.04 0.01
2.48 0.43
Irrigation water
41
Rguea irrigation water
42
Hassan Dakhil Barrage
F.B. Salah
Errachidia
13.6 1.4
14.8 1.7
2.52 0.34
1.94 0.19
2.5 0.1
}
1.9 0.2
}
0.75 0.09
}
0.19 0.02
}
27
28
29
30
31
Tap
32
33
34
35
36
37
a
b
First sampling.
Second sampling.
(c): Commercialized mineral water.
(s): Water from spring
U (mBq l 1)
U/238U
226
Ra (mBq l 1)
228
Ra (mBq l 1)
228
Ra/226Ra
226
Ra/238U
O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
Locality
Sample
O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
183
different decay series, in which the parent 232Th and 238U have quite dissimilar
chemical behaviours in aquifers.
The radioactive disequilibrium between the two uranium isotopes, 238U and its
daughter 234U in natural waters is well known (Cherdyntsev, 1971; Asikainen, 1981;
Dickson & Davidson, 1985; Cuttell, Lloyd, & Ivanovich, 1986; Andrews & Kay,
1983; Chalov, Tuzova, & Musin, 1964; Osmond, Cowart, & Ivanovitch, 1983; Plater,
Ivanovitch, & Dugdale, 1992). In the dissolved phase, the 234U activity is generally in
excess compared to that of 238U resulting in a 234U/238U activity ratio >1. The
genesis of this excess is attributed to processes like preferential leaching of 234U
(Rhosolt, Shields, & Garner, 1963; Hussain & Krishnaswami, 1980), in situ decay of
alpha recoiled 234Th (Kigoshi, 1971) or leaching through alpha-recoil tracks
(Fleischer & Raabe, 1978; Fleischer, 1980). The 234U/238U activity ratio varied
between 0.79 for the sample presenting the elevated 238U activity and 2.83. Hussain
and Krishnaswami (1980), and Cowart and Osmond (1974) have observed a reverse
correlation between 234U/238U activity ratio and 238U concentration in well water
samples from regions near Ahmedabad and in aquifers from Southern Texas. They
have attributed this finding to changes in the oxidizing/reducing conditions of the
aquifer environment, with high 238U and low 234U/238U in the oxidizing zones and
low 238U and high 234U/238U in the reducing zones. Our results showed four activity
ratio values of 234U/238U 51, four others slightly >1 and seven ratios 52. Only the
lowest value of 234U/238U was correlated with the highest value of 238U activity that
is related to 238U concentration, whereas the other points did not show any evident
correlation between the two measured parameters.
3.2. Mineral springs
Unlike well waters, the 238U activity in hot springs water, seems to show a
decreasing trend with increasing 226Ra activity and 234U/238U activity ratio (mean
values have been considered to establish this trend). Except the commercialized
Oulmes water sample that is poor in uranium and rich in radium, 238U activity
ranged from 5 to 9 mBq l 1 with a mean activity value of 6 mBq l 1 that is clearly
lower than that of well water value. The 226Ra activity ranged from 9 to
3696 mBq l 1 with a mean value higher than 650 mBq l 1. A comparison of the
uranium and radium activities in mineral water show that large amounts of 226Ra do
not necessarily indicate a high concentration of 238U in the surrounding rocks. Often
such an anomaly is caused by radium that has migrated from other areas and been
deposited randomly in the fissures of the bedrock. The measured 226Ra/238U ratio
ranged from 1.8 to 2115.
The 234U/238U activity ratio in mineral waters was obviously higher than in waters
from the other sources. The reverse trend in 238U activity vs. 234U/238U activity ratio
suggests that the elevated temperatures and strong reducing conditions in depth in
geothermal systems cause an acceleration of isotopic exchange processes (Cowart &
Osmond, 1974; Kronfeld & Adams, 1974).
In geothermal sources where the temperature and the concentration of chlorine
are very elevated and the reducing potential is very weak, the 226Ra/238U ratios are
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O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
often very large. Zukin, Harmond, Ku, and Elders (1987), and Herczeg, Simpson,
and Anderson (1988) have established in samples of geothermal origin, ratios in
order of 103–104. Indeed, in a reducing medium where uranium is much less mobile
than radium, the disappearance of sulphates allow more concentration of radium in
solution (Beaucaire & Toulhoat, 1987).
3.3. Rivers
In river water, 238U and 226Ra activities did not cover wide ranges, they varied
from 9.7 to 28 mBq l 1 for 238U and from 0.8 to 5.3 mBq l 1 for 226Ra. In case of
wells, variation ratios were about 69 times for 238U and about 25 times for 226Ra. In
case of mineral waters, except Oulmes water sample , it was about 4 times for 238U
and higher than 130 times for 226Ra. This suggests that there is no large variation in
environmental conditions of investigated rivers. The activity average was
17.6 mBq l 1 for 238U and 2.1 mBq l 1 for 226Ra. They presented, respectively,
about 3.3 and 3 10 3 times of the activity averages in mineral waters and about
0.27 and 0.21 times in well waters. The 226Ra/238U was very low in analyzed river
waters and covered a range from 0.04 to 0.38 without any evident correlation
between uranium and radium activity variations. In surface, radium concentrations
are generally lower than uranium concentrations. They are controlled by different
mechanisms in the environment, and several types of chemical reactions may take
place in the riverine environment. Redox reactions strongly affect the chemistry of
uranium which can pass from solution into reducing river bottom sediments (Lewis,
1976). Radium concentrations in natural waters are limited either by adsorption or/
and by solid solution formation. Riese (1982) found that adsorption of Radium is
inhibited by low pH and by high concentrations of calcium because of H+ and
Ca++ compete with Ra for adsorption sites. There are many chemical and physical
circumstances in which Radium is adsorbed on or desorbed from associated
sediments. Previous works showed an extremely large range of variation in uranium
and radium contents of river water. For example, the 238U activity varied from
0.2 mBq l 1 for the Amazon to 82 mBq l 1 for the Ganges and the 226Ra activity
ranged from 0.8 mBq l 1 in the St Lawrance river to 33.4 mBq l 1 in the Ganges river
(Scott, 1982). 238U activities higher than 17,000 mBq l 1 were found in the surface
water of Lodeve basin located on the uranium-bearing area in France (El bouch,
1996).
The uranium activities can also be affected by salinity and seasonal variations.
Indeed results reported in Ivanovich and Harmon (1992) show seasonal variations in
238
U activity of a factor of 2–3 without obviously changing 234U/238U ratio. The
variation represents a random sampling of what is probably a fluctuation influenced
by rainfall, run-off, and soil-leaching phenomena. These results show also a variation
of 238U activity from 10 mBq l 1 for salinity of 0% to 46 mBq l 1 for salinity of
37.2%. Our samples have been sampled in the same season of spring.
The 234U/238U activity ratios ranged from 1.07 to 2.49. The analyses of Amazon
and Mississippi river waters by Moore (1967) used as typical values in subsequent
works by other authors gave values of 234U/238U between 1.22 and 2.03.
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O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
The 228Ra/226Ra ratios are higher in rivers than in springs and wells, they ranged
from 0.51 to about 1.95. The 228Ra, daughter of 232Th is found in natural waters in
excess of equilibrium with its parent because of its ability to diffuse out of sediment
into the overlying water. The 228Ra/226Ra activity ratio changes by dilution and
radioactive decay after the water is isolated from sedimentary input. It decreases
with increasing distance from sediments and with depth within thermocline (Yamada
& Nazaki, 1986; Reid, Moore, & Sackett, 1979; Moore & Told, 1993; Schmidt &
Reyss, 1996).
3.4. Lakes, tap water, and irrigation water
Results given by tap water samples taken from six different Moroccan cities did
not present any anomalous value in uranium and radium activities, nor in 234U/238U,
228
Ra/226Ra and 226Ra/238U activity ratios. Radioactivity in tap water depends on its
source that could be rivers, dams, wells or springs. The results obtained for only
three samples did not allow us to discuss the trend of radioactive repartition of
uranium and radium isotopes in lake water. The two investigated irrigation water
samples both originated from dams located on rivers gave activities and activity
ratios comparable to those found in river water.
The minimum, mean and maximum of 238U, 226Ra and 228Ra activities and
234
U/238U, 228Ra/226Ra and 226Ra/238U activity ratios in investigated water sources
are shown in Table 2.
The data are similar to those published for other regions of the world. More
discussions have taken place in recent years about what constitutes a generally
Table 2
Minimum, mean and maximum of 238U, 226Ra and 228Ra activities and of 234U/238U, 226Ra/238U and
228
Ra/226Ra activity ratios in principal investigated sources of natural water in Morocco
Activiy (mBq l 1)
Minimum
238
Wells
Springs
Rivers
Cold Springs
Lakes
U
Ra
228
Ra
238
U
226
Ra
228
Ra
238
U
226
Ra
228
Ra
238
U
226
Ra
228
Ra
238
U
226
Ra
228
Ra
226
4.5
1
0.6
0.6
9.1
2.4
9.7
0.8
0.8
2.5
2.5
0.7
6
0.8
0.6
Mean
66
9.8
5
5.3
651
91.5
17.6
2.1
1.9
4.8
7.3
2.2
13
8.2
4.1
Activity ratio
Maximum
309
25
17.3
8.5
3696
620
27.8
5.3
2.9
8.3
10.5
3.3
24
23
11
234
238
U/ U
Ra/238U
228
Ra/226Ra
234
U/238U
226
Ra/238U
228
Ra/226Ra
234
U/238U
226
Ra/238U
228
Ra/226Ra
234
U/238U
226
Ra/238U
228
Ra/226Ra
234
U/238U
226
Ra/238U
228
Ra/226Ra
226
Minimum
Mean
Maximum
0.79
0.07
0.04
0.97
1.8
0.05
1.07
0.04
0.51
2.53
0.86
0.27
0.87
0.04
0.48
1.54
0.47
0.70
4.45
342
0.13
1.66
0.16
1.13
4.85
3.00
0.30
1.05
0.89
0.66
2.83
1.14
1.59
7.39
2115
0.19
2.49
0.38
1.95
8.30
4.79
0.31
1.16
2.48
0.76
186
O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
acceptable level of individual risk in the world. A consensus exists for substances to
which large number of people are exposed involuntarily via media such as food and
water. The Annual Limits of Incorporation (LAI) by ingestion recommended par the
International Commission of Radioprotection (CIPR) are 5 104 Bq/y for 238U,
4 104 Bq/y for 234U, 7 103 Bq/y for 226Ra and 9 103 Bq/y for 228Ra. Assuming
an individual annual consummation of 900 l of water (about 2.5 l per day), the
equivalent doses to the maximal activities measured in all samples are 278 Bq/y for
238
U, 220 Bq/y for 234U, 3326 Bq/y for 226Ra and 558 Bq/y for 228Ra. These doses
present, respectively, LAI percentages of 0.56, 0.55, 48 and 6.2%. This calculation
shows, that all measured activities are inferior to the maximum contaminant levels
recommended by the International Commission of Radioprotection and they do not
present any risk for public health in Morocco.
4. Conclusions
Radiochemical analyses of 42 natural water samples taken from different origins
(wells, springs, rivers, lakes and tap water) show, for each source, comparable results
(238U, 226Ra and 228Ra activities; 234U/238U, 228Ra/226Ra and 226Ra/238U activity
ratios) to those reported in previous works for different regions in the world. The
main conclusions include the following points:
(1) The 238U activities are higher in wells than in the others sources, and unlike well
waters, the 238U activity in the mineral hot water seems to show a decreasing
trend with increasing 226Ra activity and 234U/238U activity ratio. A comparison
of the 238U and 226Ra activities in mineral waters show that large amounts of
226
Ra do not necessarily indicate a high concentration of uranium in the
surrounding rocks, but is caused by migration of radium from other areas that
has been deposited randomly in the fissures of the bedrock.
(2) The reverse trend in 238U activities vs. 234U/238U activity suggests that the
elevated temperatures and strong reducing conditions at depth in geothermal
systems cause an acceleration of isotopic exchange processes.
(3) In river water, 238U and 226Ra activities varied in narrow ranges. This suggests
that there is no large variation in environmental conditions of investigated
rivers.
(4) The uranium and radium isotope activities measured in analyzed natural water
samples are comparable to those reported in previous works throughout the
word, and do not show any significant radioactive pollution.
(5) The calculation of equivalent doses to the maximal activities for each isotope
show that all the measured activities are inferior to the maximum contaminant
levels recommended by the International Commission of Radioprotection and
they do not present any risk for public health in Morocco.
We cannot generalize the obtained results for all natural water in Morocco
because of the limited analyzed sample numbers. They gave a general idea of
O.K. Hakam et al. / J. Environ. Radioactivity 57 (2001) 175–189
187
uranium and radium radioisotopes activity repartition in some sources of natural
water which could be used to orient the next samplings in order to establish a global
distribution map of radioelements in natural waters of Morocco.
Acknowledgements
Alpha spectrometry analysis benefited from the assistance of the Laboratoire des
Sciences de Climat et de l’Environnement, Laboratoire Mixte CNRS/CEA, Gif Sur
Yvette, France. Gamma spectrometry analysis were realized in the Laboratoire
Souterrain de Modane (LSM-Centre National de la Recherche Scientifique (CNRS/
CEA, France). We thank E. Jahjouh, S. Semghouli, H. Kafsaoui and F. Boujghal for
their help during the field campaigns. We are grateful to R. Messoussi for his
language assistance.
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