PII:
Wat. Res. Vol. 34, No. 11, pp. 2941±2950, 2000
7 2000 Published by Elsevier Science Ltd. All rights reserved
Printed in Great Britain
S0043-1354(99)00370-X
0043-1354/00/$ - see front matter
www.elsevier.com/locate/watres
RADIOECOLOGICAL STUDY OF AN ESTUARINE SYSTEM
LOCATED IN THE SOUTH OF SPAIN
J. P. BOLIVAR1*, R. GARCIA-TENORIO2 and F. VACA1
1
Dept. FõÂ sica Aplicada, E.P.S. La RaÂbida, Universidad Huelva, 21819-Palos de la Fra, Huelva, Spain
and 2Dept. FõÂ sica Aplicada, E.T.S. Arquitectura, Universidad de Sevilla, Avda Reina Mercedes s/n,
41012, Sevilla, Spain
(First received 1 December 1998; accepted in revised form 1 November 1999)
AbstractÐA big fertilizer industrial complex and a vast extension of phosphogypsum piles (12 km2),
sited in the estuary formed by the Odiel and Tinto river mouths (south-west of Spain), are producing
an unambiguous radioactive impact in their sourrounding aquatic environment, through radionuclides
from the U-series. The levels and distribution of radionuclides in the dierent water phases of this
estuarine system (®ltered and particulate fractions) have been determined. The analyses of radionuclide
concentrations and activity ratios have provided us with interesting information with which to evaluate
the extension, degree and routes of the radioactive impact, as well with the knowledge of the dierent
pathways followed for the radioactive contamination which disturbs this natural system. The obtained
results indicate that the main pathway of radioactive contamination of the estuary is through the
dissolution in its waters of the radionuclides released by the industrial activities and their later ®xation
on the particulate materials. On the other hand, the tidal activity plays an important role in the
transport and homogeneization along the estuary of the radioactivity released from the fertilizer plants.
Additionally, the results obtained for the dierent studied natural radionuclides (U-isotopes, Thisotopes and 210Po) in the ®ltered and particulate fractions have provided very rich information about
their dierent environmental behaviour in this aquatic system. 7 2000 Published by Elsevier Science
Ltd. All rights reserved
Key wordsÐestuary, phosphogypsum, natural radioactivity, contamination pathways, alpha-spectrometry, dissolution/suspended matter
INTRODUCTION
The Odiel and Tinto rivers are located in the southwest of Spain, discharging their waters into the
Atlantic Ocean. Their mouths conform an estuarine
tidal system that sourrounds a large industrial
chemical complex where several plants are placed
devoted to the production of phosphoric acid and
phosphate fertilizers (Fig. 1). In these factories,
phosphoric acid is obtained through the chemical
treatment of phosphate rock, mainly formed by
phosphorite mineral, which contains high levels of
radionuclides from the uranium series. Additionally,
in this chemical process a by-product called phosphogypsum (PG) is formed, which is generally
stored in the surroundings of the factories. Because
this by-product accumulates a signi®cant fraction of
the radioactivity contained originally in the mineral,
it can be concluded that these industries could produce an important radioactive impact on their
*Author to whom all correspondence should be addressed.
Tel.: +34-959350651; fax: +34-959350311; e-mail:
bolivar@uhu.es
nearby environment (Bolivar, 1995; Rutherford et
al., 1994; Bolivar et al., 1995a, 1996a). At the time
of the sampling, these factories were processing
annually over 2 106 metric tons of phosphate
rock, and they generate about 3 106 tons of PG.
The PG stacks cover about 12 km2 on the salt
marshes of Tinto River and therefore they generate
a high radioactive impact on this marsh-land (BolõÂ var, 1995; Bolivar et al., 1995b). On the contrary,
the salt-marshes of the Odiel river are not physically
perturbed and have been recently declared a natural
reserve by the regional goverment.
In previous works we have determined the radioactivity distribution in the phosphoric acid production process of the factories sited in the estuary
(Bolivar et al., 1993, 1995a, 1996a). We concluded
in these studies that more than 90% of Po and Ra
originally present in the phosphate rock remains in
the phosphogypsum, while the percentage of U is
much lower (<20%). It is also known that the
behaviour of 210Pb in the production processs of
phosphoric acid used in the factories is quite similar
to the 226Ra (Guimond and Hardin, 1989).
The radioactive impact generated by this indus-
2941
2942
J. P. Bolivar et al.
trial complex in the sediments and waters of this
estuary was widely studied in previous works (MartõÂ nez-Aguirre et al., 1994; Garcia-LeoÂn et al., 1997),
but these studies were devoted to evaluating this
impact in those zones of the rivers quite close to
the possible sources of radioactive contamination:
the fertilizers industries and the PG piles.
In this work, we extend these studies to more
remote zones in the rivers, electing for that two
areas (Fig. 1): the common channel of the Odiel
and Tinto river (called Ria de Huelva) and the
Estero Domingo Rubio (a rivulet that ends in the
Tinto river, opposite the PG piles). Through this
study we can evaluate more properly the extension
and degree of contamination produced by the factories, and gain knowledge about the behaviour of
several natural radionuclides in estuarine systems.
The actual situation of the Ria de Huelva was
conformed 30 years ago when an arti®cial dike was
built (Fig. 1) for the construction of a new harbour,
the water exchange rate of the rivers with the
Atlantic Ocean being changed as a consequence. On
the other hand, the water ¯ow that comes from the
rivers is much smaller than the water volume
exchanged with the ocean, a fact that can be
deduced from the uniform values of pH (in the
region of 6.5±7) and from the salinity determined in
the waters of the estuary, which are quite similar to
those found in coastal seawaters of this geographical area. On the contrary, the pH values in the
waters of both rivers, upstream of the estuary, are
very low (between 2 and 3) due to the in¯uence of
some mining activities developed historically within
their margins.
Additionally, the study of the distribution of the
dierent radionuclides between the ®ltered and particulate phases, can provide interesting information
about their behaviour in this aquatic system. It can
also allow the rati®cation of the theory about the
main contamination pathways of the estuary.
MATERIALS AND METHODS
The main criterion in the sampling strategy was to select
a set of points distributed uniformly along the zone in
study, which was the estuarine area more remote from the
fertilizer industrial complex and the PG piles. A total of
13 sampling points were selected, as illustrated in Fig. 1.
At each sampling location, two water samples were collected: one corresponding to high tide (code {H}) and the
other one to low tide (code {L}). Eight sites (OT1±OT8)
correspond to the Ria de Huelva, while only ®ve sites
(DR1±DR5) were elected from the Estero Domingo Rubio
rivulet. In both cases the numbering increases in the direction of the water ¯ow.
About 20 L of water per sample was collected. Immediately after the collection, they were ®ltered using polycarbonate ®lters of 14.2 cm diameter and 0.2 mm pore size.
After ®ltration, about 100 ml of concentrated HNO3 was
added to each ®ltered fraction to establish its pH at
around 1±2 and consequently to avoid the adsorption of
the actinides on the container walls and the growth of
micro-organisms. The code {W} was assigned to the ®ltered fraction and {F} to the particulate fraction.
Alpha emitting radionuclides (210Po, U and Th isotopes)
were measured in the dierent phases by alpha-particle
spectrometry using ion-implanted silicon detectors. The
suspended matter determinations were done placing the ®lters in an ultrasonic bath containing hydrochloric acid for
Fig. 1. Map of the Odiel and Tinto river mouths. The location of Huelva Town, fertilizer plants, phosphogypsum piles and the 13 sampling points are specially marked.
Radioecological study of an estuarine system
30 min. Then, the ®lters were cleaned with nitric acid and
the liberated particulate matter was dissolved applying an
acid
atmospheric
digestion
with
aqua
regia
(3HCl:1HNO3). The dry residue was redissolved in 8 M
nitric acid. Afterwards, the isolement of U, Th and Po
was carried out through a sequential solvent extraction
technique, intially developed by Holm and Fukai (1977)
and slightly modi®ed for us.
In the case of water samples, 1 L of the ®ltered water
was taken for 210Po and U-isotopes analyses, while 5 L
were necessary for the Th-isotopes studies. The Fe3+ carrier was added and actinides and Po were co-precipitated
with Fe(OH)3 by adding drop-wise NH4OH until pH=8±
9. Then, the Fe(OH)3 precipitate, containing U, Th and
Po, was isolated by ®ltration, re-dissolved in 10 ml 8 M
HNO3 and the TBP method previously described for the
suspended matter was applied.
210
Po was self-deposited onto silver discs from a 2 M
HCl solution (El-Daoushy et al., 1991), while the ®nal solutions of U and Th were electroplated onto stainless steel
discs by the method of Hallstadius (Hallstadius, 1984).
For the total recovery determination, and at the beginning
of the radiochemical process, known amounts of
208
Po,232U or 229Th were added into each sample as isotopic tracers.
RESULTS AND DISCUSSION
Table 1 shows the physical properties measured
in all the water samples. It can be seen that the
average temperature of the Ria de Huelva water at
low tide (18.4 2 0.28C) is slightly higher than that
obtained at high tide (17.6 2 0.18C). This fact indicates that the temperature of the oceanic water
entering in the estuary was a little bit lower in comparison with the fresh-water coming from the rivers.
In relation to the pH, a smooth increase of this
2943
value towards the Atlantic Ocean is observed in Ria
de Huelva and in both tidal cycles. This trend is
probably generated by the mixing of the oceanic
waters (pH 0 8) with the river waters (pH 0 2.5),
which is very low due to the mining activities developed in their basins since the 19th century, and the
in¯uence of the industrial complex euents.
Although the river ¯ow water is very small in relation to the marine ¯ow, a dierence in the order
of magnitude of 5±6 in the H+ concentration can
change the pH of the estuarine water a little bit,
mainly formed by sea water. In Table 1, it is
observed that pH 1 8 (typical of sea water) is
found at high tide in the samples nearest to the
Atlantic Ocean, ratifying the previous hypothesis.
On the contrary, no special trends were observed in
the pH values along the Domingo Rubio rivulet
(around seven in all the samples).
Finally, and concerning the values of the electrical conductivity, only to notice its constancy along
the Ria de Huelva with values typical of surface sea
waters, while this magnitude in the Domingo Rubio
waters increases towards its mouth, showing this
fact the mixing with waters from the estuary. In
fact, it can be observed that the value of the electrical conductivity in sample 1 is typical of freshwater, while the value in sample 5 (collected in the
mouth of the rivulet) is quite similar to the obtained
ones in the Ria de Huelva channel.
Radioactivity in the ®ltered fraction
Ria de Huelva channel. The concentrations of Uisotopes, Th-isotopes and 210Po determined in the
®ltered waters of the Ria de Huelva at high and
Table 1. Some physico-chemical properties of the water samples collected in the analysed zones of the Odiel and Tinto river estuary.
{RH}=Ria de Huelva channel, {DR}=Domingo Rubio rivulet
Sample
High tide (RH)
1
2
3
4
5
6
7
8
Average
Low tide (RH)
1
2
3
4
5
6
7
8
Average
Global average (RH)
DR
1
2
3
4
5
T (8C)
pH
Suspended matter (mg/l)
Conductivity (mS/cm)
17.7
17.7
17.8
17.7
17.7
17.6
17.6
17.1
17.620.1
6.7
6.7
7.0
7.4
7.7
7.8
8.2
8.1
7.420.2
42.3
37.6
39.5
54.0
27.3
37.1
33.1
36.3
38.422.7
38.3
38.4
39.1
39.0
39.1
39.2
38.6
38.2
38.820.1
18.0
18.0
18.1
18.3
18.1
20.1
18.3
18.2
18.420.2
18.020.1
6.3
6.9
6.7
6.6
6.9
6.9
7.0
7.3
6.820.1
7.120.1
21.3
22.4
18.2
36.2
64.6
48.5
50.3
28.6
36.325.9
37.323.1
37.3
35.3
38.0
38.2
38.9
39.0
38.4
39.7
37.120.5
38.423.0
17.2
20.5
17.6
17.5
18.0
7.2
6.7
7.2
7.6
7.2
148
13.2
25.1
27.1
33.8
0.47
10.9
20.9
25.5
33.0
2944
J. P. Bolivar et al.
Table 2. Activity concentrations (Bq/kg) measured in the ®ltered water fractions. {RH}=Ria de Huelva channel, {DR}=Domingo
Rubio rivulet. N.M.=not measured; N.D.=not detected
238
U
Sample
High tide (RH)
HW1
HW2
HW3
HW4
HW5
HW6
HW7
HW8
Average
Low tide (RH)
LW1
LW2
LW3
LW4
LW5
LW6
LW7
LW8
Average
Global average
DR
W1
W2
W3
W4
W5
235
U
234
U
210
Po
232
Th
230
Th
228
Th
28.622.3
24.221.9
30.823.8
36.622.9
40.823.2
43.424.0
43.723.8
45.823.2
37.722.8
1.0320.3
0.920.2
N.M.
1.420.4
1.120.3
2.320.6
1.420.5
1.720.3
1.4020.17
28.922.3
26.022.0
41.824.7
49.523.7
43.523.4
48.224.3
51.924.4
45.423.2
41.923.4
10.921.0
5.220.6
2.1420.30
47.023.1
4.2020.77
5.3320.40
3.6320.26
2.0920.17
10.125.3
N.M.
N.D.
0.1920.08
0.7920.15
0.6020.25
0.5920.08
0.5320.07
0.3420.06
0.5120.09
N.M.
2.4920.30
2.5220.32
1.9120.25
1.8920.47
3.0220.21
2.1920.17
2.1120.18
2.3020.15
N.M.
1.8320.25
1.3820.23
1.5320.22
2.2920.53
1.9420.15
1.7120.14
1.5620.15
1.7520.12
63.824.8
14.521.9
38.923.0
33.122.8
34.522.8
35.022.8
85.326.0
36.822.9
42.727.7
39.725.9
2.820.6
0.720.4
N.M.
1.820.4
1.220.3
1.720.4
3.220.6
1.620.4
1.8620.32
1.6320.19
61.624.7
15.522.0
43.623.3
37.223.1
41.823.3
39.023.1
147210
45.523.4
53.9214
47.927.7
22.721.6
1.2420.30
23.021.6
5.6320.58
2.5620.43
3.0720.45
11.121.1
3.1720.43
9.123.2
9.623.0
1.5420.29
N.M.
0.9020.13
0.3720.07
0.2520.06
0.1020.04
N.M.
N.M.
0.6320.26
0.5620.12
5.6820.67
N.M.
2.0120.21
1.2020.13
1.9120.18
1.0120.12
N.M.
N.M.
2.3620.85
2.3320.36
1.3020.26
N.M.
1.6920.19
2.2620.19
2.4220.22
2.0020.18
N.M.
N.M.
1.9320.20
1.8320.11
9.820.7
8.120.6
21.921.3
29.822.6
30.822.5
0.6220.11
0.6620.11
1.0220.14
1.520.4
1.220.3
10.420.7
8.220.6
23.821.4
29.222.5
30.122.5
1.1820.13
2.4720.21
5.9120.48
5.5120.54
11.620.9
1.2720.22
1.1020.30
0.9520.16
2.1020.40
N.M.
2.1820.30
1.0220.28
2.3620.24
1.9620.39
N.M.
1.9820.28
5.420.79
2.3920.27
2.0920.40
N.M.
low tide are shown in Table 2. From the obtained
results, it is clear than the 234U and 238U activity
concentrations are very uniform in solution during
high tide, while there are two activity peaks during
the low tide at sampling points 1 and 7 (Fig. 2), indicating the existence of some contamination
``bags'' along the channel with its origin probably
in the contamination associated with the fertilizer
activities. These ``bags'' are more easily detectable
Fig. 2.
238
at low tide due to the smaller amount of clean sea
water entering the estuary.
The average values of the 238U concentrations in
low and high tides are 43 2 7 mBq/l and 38 2 3
mBq/l respectively, in the range of the concentrations found in uncontaminated surface sea
waters, 40 mBq/l (Ku et al., 1977; Borole et al.,
1977). This fact indicates that except in some
speci®c locations, the possible contamination of U-
U activity concentrations in solution for the Ria de Huelva at high and low tide.
Radioecological study of an estuarine system
isotopes in the dissolved form is masked for the
high mobility of these radionuclides and consequently for their relatively high values in clean sea
waters.
Concerning the 210Po concentrations, they are
generally lower than the U-isotopes along the channel but generally higher than the normal values
found in unperturbed estuarine waters, 2 mBq/l
(Iyengar et al., 1981), indicating the possible 210Po
impact of the fertilizer activities in this compartment. The average 210Po activity concentration
along the channel, shown in Table 2, is 1023 mBq/
l with activity peaks up to 4723 mBq/l, and with a
value in sample HW8 (high tide and therefore a
sample with the highest marine in¯uence) of 2.1 2
0.2 mBq/l, which could be considered the background value for 210Po of this geographical area.
This value was also obtained in another water
sample collected in open sea, located 40 km from
this estuary.
On the other hand, the 232Th concentrations are
two orders of magnitude smaller (average value 0.56
2 0.12 mBq/l) than those found for U-isotopes, indicating its tendency to be associated to the particulate matter (Koczy et al., 1957). The 232Th
concentrations are also smaller than those of its
daughter 228Th (average value of 1.8 2 0.1 mBq/l).
This last fact can be explained by the higher solubility of Ra than Th in sea waters, and because the
228
Th concentrations in solution are mainly governed by its progenitor 228Ra due to its major halflife. Clear enhancements can also be observed in
the concentrations of 230Th in relation to232Th
(about ®ve times higher), which could be generated
2945
by the wastes from the fertilizer plants released into
the estuary.
Some of the activity ratios in the ®ltered waters
along the channel, together with their average
values, are compiled in Table 3 for high and low
tidal cycles. The average 234U/238U activity ratio
was 1.17 2 0.05, similar to the one found in unperturbed sea waters (Moore and Sackett, 1964; Borole
et al., 1982), and re¯ecting an undetectable input of
U from the factories to this area. On the contrary,
the 230Th/232Th activity ratios are clearly higher
than one, ranging from 2.4 to 9, and with an average value equal to 5.421.0, which shows the arti®cial input of 230Th because in unperturbed waters
this ratio is around the unity.
The average 230Th/234U activity ratio was 0.0532
0.006, very far from the secular equilibrium, showing the extremely low mobility of thorium in sea
water in relation to uranium. However, this activity
ratio is clearly higher than the value found in
uncontaminated sea waters (R10ÿ2) (Scott, 1982)
which con®rms the detectability of some anthropogenic inputs in solution of 230Th in these estuarine
waters. Obviously the average 232Th/234U activity
ratio is also very low (0.012 2 0.002) due to the
strong anity of Th with the particulate matter and
the high mobility of U.
On the other hand, the average 210Po/234U activity ratio in the ®ltered waters along the estuary
(0.2120.06), higher than the value of 0.05 found in
unperturbed sea waters (Bacon and Elzerman,
1980), indicates, as was stated before commenting
on the absolute 210Po concentrations, a detectable
enrichment of 210Po in relation to U in these waters.
Table 3. More signi®cant activity ratios determined in solution. N.M.=not measured
Sample
High tide (RH)
HW1
HW2
HW3
HW4
HW5
HW6
HW7
HW8
Average
Low tide (RH)
LW1
LW2
LW3
LW4
LW5
LW6
LW7
LW8
Average
Global average
DR
W1
W2
W3
W4
W5
230
Th/
232
Th
234
U/238U
228
Th/232Th
232
Th/234U (10ÿ3)
230
Th/234U (10ÿ2)
210
Po/234U (10ÿ1)
210
Po/230Th
N.M.
N.M.
1325
2.420.5
3.221.4
5.220.7
4.120.6
6.121.2
5.721.4
1.0120.07
1.0720.08
1.3620.17
1.3520.09
1.0720.07
1.1120.09
1.1920.09
0.9920.05
1.1420.05
N.M.
N.M.
723
1.920.4
3.821.7
3.320.5
3.220.4
4.520.9
3.920.8
N.M.
N.M.
4.521.9
16.023.2
13.821.0
12.221.9
10.221.5
7.521.4
10.721.7
N.M.
9.621.3
6.020.9
3.920.6
4.321.1
6.320.7
4.220.5
4.620.5
5.620.7
3.820.4
2.020.3
0.5120.09
9.520.9
0.9620.18
1.1120.12
0.7020.07
0.4620.05
2.421.1
N.M.
2.120.3
0.8520.15
24.623
2.2220.68
1.7620.17
1.6620.17
0.9920.11
4.923.3
3.720.7
N.M.
2.220.3
3.320.6
7.521.8
923
N.M.
N.M.
5.121.3
5.421.0
0.9720.06
1.0620.16
1.1220.07
1.1220.09
1.2120.08
1.1220.08
1.7220.07
1.2420.08
1.2020.08
1.1720.05
0.8420.22
N.M.
1.920.3
6.121.2
9.522.3
1826
N.M.
N.M.
7.323.0
5.421.5
2525
N.M.
2023
9.922.2
6.021.5
2.621.0
N.M.
N.M.
12.724.2
11.622.0
9.221.3
N.M.
4.620.5
3.220.4
4.620.5
2.620.4
N.M.
N.M.
4.821.1
5.320.6
3.720.4
0.8020.20
5.320.5
1.5220.19
0.6220.10
0.7920.12
0.7620.09
0.7020.12
1.820.5
2.120.6
4.020.3
N.M.
1121
4.720.6
1.420.2
3.020.5
N.M.
N.M.
4.821.6
4.922.0
1.720.3
0.920.3
2.520.4
0.920.2
N.M.
1.0720.06
1.0120.06
1.0920.04
0.9820.08
0.9820.07
1.620.3
4.921.4
2.520.4
0.9720.24
N.M.
122221
134230
4027
74215
N.M.
2123
1223
9.921.1
6.721.4
N.M.
1.1320.12
3.020.3
2.520.2
1.920.2
3.920.4
0.5420.11
2.420.7
2.520.3
2.820.6
N.M.
2946
J. P. Bolivar et al.
This activity ratio reaches the highest values also in
the samples nearest to the contamination source.
Then we can conclude that in general there are
no signi®cant dierences between the average concentrations and activity ratios at high and low tide,
considering the experimental uncertainties, and
from these data we can establish the following
order in activity concentrations (®ltered fraction)
along the channel: [U] > [210Po] > [230Th] > [228Th]
> [232Th].
Domingo Rubio rivulet. Table 2 (code {DR})
also shows the U-isotopes, Th-isotopes and 210Po
concentrations in solution. In Fig. 3 a good correlation between the electrical conductivity and U
concentrations can be seen. This fact, together with
the decrease of the U-isotopes and 210Po concentrations with the distance from its mouth, re¯ects
the entrance of waters from the Tinto river channel
enriched in U-series radionuclides.
In relation to the activity ratios, we can indicate
that in general they present some variations in comparison with the obtained ones in the Ria de
Huelva channel. The 234U:238U activity ratio is
close to 1, which is lower than the typical value of
1.14 measured in uncontaminated surface waters. In
addition, the 230Th/232Th activity ratios (Table 3)
are lower than in the Ria de Huelva, with values
for 232Th and 230Th concentrations higher and similar to those found in the Ria de Huelva channel respectively, even in the sample W1 not aected by
the tidal cycles (fresh water sample). Finally, it is
possible to observe the decrease of the 230Th/234U
toward the rivulet mouth, showing again that the
Fig. 3.
238
U and
210
inputs of dissolved U from the estuarine waters are
dominant.
Radioactivity in particulate matter
Ria de Huelva channel. The activity concentrations in the particulate matter fraction in the Ria
de Huelva channel are shown in Table 4, while
their activity ratios are shown in Table 5. In general, we can observe that the activity concentrations
of U-isotopes are higher than in unperturbed estuaries. Martin et al. (1978) estimated a world-wide
average concentration in particulate matter of 3
ppm, about 35 Bq/kg of 238U, with some ¯uctuations depending on the geographical areas. The
higher concentrations are particularly found at the
®rst three sampling points (for both high and low
tide) decreasing until point 4, and are, from this location, quite uniform until reaching the Atlantic
Ocean. It is interesting to note that it is even possible to ®nd relatively high levels of U-isotopes at
high-tide in the zone close to the Atlantic Ocean
(about 100 Bq/kg of 238U at location 8).
The 210Po concentrations again have values
higher than in typical estuaries, being in similarity
to U the most contaminated samples are located
nearest the fertilizer industries and the PG piles.
Speci®cally, it is observed that point 1 at low tide,
is the most contaminated sample for U-isotopes
and that 210Po, occurs the same in the dissolved
fraction. Consequently the maximum U and 210Po
concentrations observed in a determined zone of
the channel can be associated with the movement
down it of some of the euents released directly or
indirectly from the fertilizer plants. These contami-
Po activity concentrations, and electrical conductivity in the ®ltered water fractions
from Domingo Rubio rivulet water samples.
Radioecological study of an estuarine system
2947
Table 4. Activity concentrations (Bq/kg) measured in the particulate matter fraction. {RH}=Ria de Huelva channel, {DR}=Domingo
Rubio rivulet. N.M.=not measured; N.D.=not detected
238
Sample
High tide (RH)
HF1
HF2
HF3
HF4
HF5
HF6
HF7
HF8
Average
Low tide (RH)
LF1
LF2
LF3
LF4
LF5
LF6
LF7
LF8
Average
Global average
DR
F1
F2
F3
F4
F5
235
U
234
U
210
U
232
Po
230
Th
Th
339234
635257
388231
123211
112220
100214
122216
144212
245268
N.M.
25.624.8
18.823.0
6.021.4
1224
3.321.9
6.422.9
4.421.1
10.922.9
345234
714263
424234
127212
81216
98214
129217
176214
262278
14129
270224
198222
12628
134210
10228
208230
161213
167219
9.222.1
9.922.0
16.323.3
12.022.1
20.026.7
15.022.3
39.028.6
29.224.4
18.823.7
49.625.9
63.626.2
126212
69.626.2
115218
69.526.0
146221
99210
92212
1165283
131210
337232
55.624.6
45.824.1
70211
123212
24.522.4
2442136
245273
43.724.7
N.M.
N.M.
N.M.
N.M.
N.M.
5.621.4
N.M.
±
±
1021273
131210
330231
53.324.4
41.423.8
70211
138214
28.122.7
2272118
244264
450237
93.827.5
308220
64.525.1
68.326.5
70.725.9
10626
48.923.9
151252
159227
N.M.
N.D.
19.224.2
3.521.2
15.824.0
1023
13.224.1
8.722.4
11.722.1
15.822.4
N.M.
41.729.1
124213
24.523.5
33.326.0
2629
58210
26.724.5
48213
72211
28.724.1
473239
10029
113211
274220
1.920.8
2525
4.221.2
5.721.7
13.021.8
34.724.7
508242
114210
121212
285221
102210
249227
117210
9829
102211
31.022.7
30.326.7
11.723.3
11.223.0
7.821.5
34.723.0
53.829.3
110213
53.726.3
52.724.7
nation ``bags'' (PeriaÂnÄez, 1995) generated during
both high and low tides (minimum water speed) travel across the principal channels of the estuary due
to the tidal activity and they will give activity peaks
in certain zones. However it is also interesting to
point out that the zone where the highest values for
U and Po in particulate matter are observed, represent the zone where the Tinto and Odiel waters
mix, where some increase in the adsorption and pre-
cipitation of the dissolved radioactivity in the water
onto the particles in suspension could be produced.
Concerning the Th-isotopes (Table 4), it can be
indicated that the 232Th concentrations are in the
range found in uncontaminated estuarine waters
(Martin et al., 1978; Moore, 1967) and present normal average values for both high and low tidal
cycles (1924 Bq/kg and 1223 Bq/kg, respectively).
On the contrary, enhancements in relation to 232Th
Table 5. More signi®cant activity ratios determined in the particulate matter fraction. N.M.=not measured
Sample
High tide (RH)
HF1
HF2
HF3
HF4
HF5
HF6
HF7
HF8
Average
Low tide (RH)
LF1
LF2
LF3
LF4
LF5
LF6
LF7
LF8
Average
Global average
DR
F1
F2
F3
F4
F5
230
Th/232Th
234
U/238U
230
Th/234U
232
Th/234U
210
Po/234U
210
Po/230Th
5.421.3
6.421.4
7.721.6
5.821.1
5.822.1
4.620.8
3.720.8
3.420.5
5.320.5
1.0220.07
1.1220.05
1.0920.05
1.0320.07
0.7220.16
0.9820.15
1.0520.15
1.2220.07
1.0320.05
0.1420.02
0.08920.012
0.2920.11
0.5520.07
1.4220.36
0.7120.12
1.1320.20
0.5620.07
0.6120.16
0.02620.007
0.01420.003
0.03820.015
0.09520.021
0.2420.10
0.1520.03
0.3020.07
0.1620.03
0.1320.04
0.4120.05
0.3820.05
0.4720.06
0.9920.11
1.6520.35
1.0420.15
1.6120.30
0.9120.10
0.9320.18
2.820.3
4.220.5
1.5720.23
1.8120.20
1.1620.20
1.4720.17
1.4220.24
1.6320.21
2.0020.36
N.M.
N.M.
6.421.5
7.022.6
2.120.6
2.521.4
4.421.6
3.120.9
4.320.8
4.920.5
0.8820.02
1.0020.06
0.9820.07
0.9620.06
0.9020.07
1.0020.16
1.1320.08
1.1420.11
1.0020.03
1.0120.03
N.M.
0.3220.07
0.3820.05
0.4620.07
0.8020.17
0.3720.14
0.4220.09
0.9520.17
0.5320.09
0.5720.10
N.M.
N.M.
0.05920.015
0.06620.026
0.3820.13
0.1520.10
0.09620.034
0.3120.10
0.1820.05
0.1520.03
0.4420.05
0.7220.08
0.9320.11
1.2120.12
1.6520.22
1.0120.18
0.7720.09
1.7820.20
1.0620.16
1.0020.12
N.M.
2.220.5
2.520.3
2.620.4
2.120.4
2.720.8
1.820.3
1.820.3
2.2420.14
2.1220.20
1.1220.09
1.8020.05
9.422.7
4.821.4
6.721.3
1.2120.07
1.0720.06
1.1520.09
1.0720.10
1.0420.04
1.0020.15
0.1120.02
0.9620.14
0.4420.07
0.1820.02
0.8920.14
0.06120.02
0.1020.03
0.0920.02
0.02720.005
2.9420.40
0.4920.07
1.0320.12
0.8120.11
0.3620.04
2.920.4
4.620.09
1.0620.15
1.8220.29
1.9320.27
2948
J. P. Bolivar et al.
are found for 230Th, but lower than those found for
U-isotopes and 210Po, being relatively uniform in its
concentration along the channel.
In fact, and ordering the studied radionuclides
for their average concentrations in the suspended
matter, we can indicate: [U] > [210Po] > [230Th] >
[232Th].
Also, and of particular interest, is that for 230Th
there can be observed some small dierence
between the average concentrations measured at
high (92212 Bq/kg) and low tide (48213 Bq/kg).
The arti®cial origin of most of the U-series radionuclides enhancements found in the particulate fraction of the waters along the Ria de Huelva channel
can be also deduced from the values obtained for
several activity ratios. For example, the average
234
U/238U activity ratio is 1.01 2 0.03, very close to
1 which is the value found in the phosphate rocks
used in the fertilizer plants (Guimond and Hardin,
1989; Bolivar et al., 1996a) while the average
230
Th/232Th activity ratio (5.1 2 0.6) indicates the
existence of enrichment from uranium series radionuclides.
However, complementary information can be
obtained by analysing the 230Th/232Th activity ratio
(similar chemical behaviour), which in suspended
matter (4.9 2 0.5) is similar to both average values
in sediments (5.920.3) (BolõÂ var et al., 1995a,b) and
in solution (5.4 2 1.0), and indicating that the contamination pathways of the sediments and suspended matter are very similar.
The global average 210Po/234U ratio is 1.0020.12
while in the fresh PG (and in the PG piles) this
ratio is about or higher than 3, illustrating that the
main pathway of contamination is through the dissolution (and, as a consequence, its content in
radionuclides) of PG released by the fertilizer plants
into the estuary and their later ®xation onto the
suspended material. This fact is rati®ed through the
other activity ratios shown in Table 5, which are
very dierent than the ratios measured in the PG
(BolõÂ var et al., 1996a).
Domingo Rubio rivulet. With regard to the suspended matter, it can also be observed in Table 2
that in the Domingo Rubio rivulet the activity concentrations for several radionuclides from the Useries are higher than those of the Th-series, in
common with the Ria de Huelva channel data.
Only the sample F1 has a normal content of natural
radioactivity, with concentrations similar to those
found in suspended matter of unperturbed estuaries
(which range from 10 to 50 Bq/kg for both series),
except for 210Po where its concentration (102 2 12
Bq/kg) can be considered similar to the one determined in other samples of this rivulet.
Additionally, observing the activity ratios
(Table 5), it is again found that the levels of 230Th
are enhanced in relation to 232Th, specially in the
samples nearest to its mouth. This isotopic activity
ratio ranges from 5 to 9 in samples F3 to F5. This
clear enrichment in the U-isotopes can be deduced
from the low values obtained for the 232Th: 234U activity ratios.
The high content of 210Po in location 1 could be
due to the high proportion in this sample of surface
materials from its surrounding soils, since this
sampling was done after a rainy day which introduced a large amount of eroded soil into this rivulet. The sample was collected in a place not aected
by the tidal activities as it was demonstrated
through its electrical conductivity typical of freshwaters and the other radioactive concentration
values. Then the particulate fraction of this sample
can be considered of terrestrial origin and it can
contain a considerable amount of atmospheric (or
unsupported) 210Pb (210Po) (El-Daoushy, 1987).
Partition coecients in Ria de Huelva
Particulate matter is an important medium of
transport for many elements. For this reason is very
important to determine the distribution of elements
between the dissolved and particulate phases of the
waters, which can be expressed by a partition coecient, K.
This coecient is de®ned in our case as the ratio
between the concentration of a radionuclide in particulate matter and its concentration in solution,
and gives information about the adsorption degree
of a radionuclide to the solid fraction. From our
previously shown data, we have calculated these
partition coecients for several radionuclides in the
Ria de Huelva channel at high and low tide, by
using the formula
K
As
l=kg
Ad
where As is the activity concentration in the particulate matter in Bq/kg and Ad is the activity concenTable 6. Partition coecients (l/kg) in the water samples collected
at the Ria de Huelva
Sample
High tide (RH)
HF1
HF2
HF3
HF4
HF5
HF6
HF7
HF8
Average
Low tide (RH)
LF1
LF2
LF3
LF4
LF5
LF6
LF7
LF8
Average
Global average
238
U (103)
210
Po (104)
230
Th (104)
232
Th (104)
11.821.2
1.2920.08
±
±
26.223.1
5.1520.45 2.5520.24
±
12.621.8
9.221.0
5.020.5
8.621.7
3.3620.40 0.26720.017 3.6420.32 1.5220.26
2.7520.53 3.1920.23
6.121.0
3.321.0
2.3020.38 1.9120.15 2.3020.20 2.5420.38
2.7920.44
5.720.8
6.720.9
7.321.5
3.1420.34
7.720.6
4.720.5
8.621.2
8.123.0
4.321.1
4.420.6
5.321.3
18.321.9
9.021.4
8.721.1
1.6820.19
1.3320.16
2.0020.35
1.4420.17
0.6720.08
5.422.2
6.821.8
1.9820.16
7.620.4
1.3420.09
1.1520.08
2.6420.25
2.3020.19
0.9520.05
1.5420.12
2.420.7
3.421.1
±
±
6.120.6
2.0420.29
1.7420.33
2.620.9
±
±
3.121.0
4.020.6
±
±
2.120.4
1.020.3
6.321.5
1023
±
±
4.822.0
5.121.1
Radioecological study of an estuarine system
tration in solution expressed in Bq/l. The obtained
K values are compiled in Table 6.
The so de®ned partition coecient coincides
under the equilibrium conditions between the two
phases with the well known equilibrium distribution
coecient (Kd). The degree of equilibrium conditions for the dierent radionuclides is not known
for the analysed samples, and in fact will be evaluated here using the values obtained for the partition
coecients together with previously shown data
and literature information about Kd values in estuarine systems.
The K values obtained for uranium do not present signi®cant dierences between both high and
low tide, with an average value of (6.8 2 1.8) 103 l/
kg, and ranging along the Ria de Huelva from 1.3
103 to 1.8 104 l/kg. These K values are in good
agreement with the Kd values found in the literature
that ranges from 0.2 103 to 5 103 l/kg, with an
average of 3 103 l/kg (IAEA, 1985; Eisma, 1993).
This agreement can indicate a good degree of equilibrium for uranium in the waters of the estuary.
Concerning the obtained partition coecients for
210
Po, it can also be commented that again there
are no signi®cant dierences between both low and
high tide, ®nding a mean value of (3.4 2 1.0) 104 l/
kg, which is ®ve times higher than the partition
coecients determined for Uranium. This fact
shows the bigger tendency of the 210Po to be associated to the particulate material in comparison with
U. The Kd recomended in the literature (IAEA,
1985) for Po is 1 104 l/kg, but this value must
only be considered as an order of magnitude since
it presents big variations in unperturbed systems.
The partition coecients for 230Th and 232Th are
very similar for the majority of the samples. It is
observed in Table 6 that they are very uniform and
the dierences between the average values for 230Th
and 232Th are not evident considering the experimental uncertainties: (4.0 2 0.6) 104 l/kg for
230
Th and (5.121.1) 104 l/kg for 232Th. However,
these K values are clearly smaller than the Kd found
in the literature (IAEA, 1985), being outside the
delimited range associated with unperturbed systems: 1 105 to 1 107 l/kg, but in the same order of
magnitude as the lower limit. These low values
found for thorium K could be related to several
facts previously commented on as the low concentrations of Th-isotopes in the suspended matter or
the existence of non-equilibrium between solid-solution phases due to the residence time of the suspended particles in the estuary and the slow rate of
transfer for Th from the water onto the particles.
CONCLUSIONS
The results obtained in this paper have shown the
signi®cant radioactive impact produced by radionuclides from uranium series in the estuary formed
by the Tinto and Odiel rivers. In this sense, activity
2949
concentrations of several uranium series radionuclides were found in the waters around one order
of magnitude higher than those of uncontaminated.
These enhancements were observed either in solution or attached onto the suspended material. It
was demonstrated that this radioactive contamination comes from the wastes produced by a phosphate fertilizer complex located close to this
estuary.
The distribution of radionuclides in the dierent
phases, analysed by this aquatic system as well as
the study of their several activity ratios, have
allowed us to con®rm the arti®cial origin of the
radioactive contamination (fertilizer plants), to
deduce that the main pathway of contamination is
through the solution in the estuarine waters of the
radionuclides released by the industrial activities
with their later deposition on the sediment material,
and to obtain information about the dierent behaviour of the isotopes analysed in this environmental
system.
The relative uniformity found in the concentrations of U and daughters along the estuary, even
in quite remote locations from the contamination
sources, and the uniformity in some activity ratios,
indicates that the tidal activity plays an essential
role in the dispersion of the radioactive contamination. This conclusion has also been con®rmed
through the analysis of the water samples collected
from a small rivulet that ends in the estuary, and
that it is also aected by inputs from the estuary
coming from it due to the tidal activities.
AcknowledgementsÐThis work has been partially supported by ENRESA, Junta de Andalucia and the CICYT
projet: 1FD 97-0900-C02-02.
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