Reprints from:

Studies in Environmental Science 68

FRESHWATER AND ESTUARINERADIOECOLOGYProceedings of an International Seminar, Lisbon, Portugal,2l-25 March 1994

Editors:

G. DesmetEuropean Commission, Directorate General )(XI!-F-6, Rue de Treves 61, 1049 Brusse/s, Belgium

R.J. BlustDepartnent of Biology, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium

R.N.J. ComansECN, Petten, The Netherlands

J.A. FernandezLJniversidad de Málaga, Campus de Teatinos dn, 29071, Málaga, Spain

J. HiltonInstitute of Freshwater Ecology, River Laboratory, Easf Sfoke, Wareham, Dorset BH20 688, UK

A. de BettencourtDepartmento de ProtecAáo e Seguranga Radiológica, DirecAáo Geraldo Ambiente, EstradaNacional 1 0, 2686 Sacavém, Portugal

Assistant Editors:

P.G. Appleby, P. Beneó, U. Bergstróm and J. Remacle

ELSEVIERAmsterdam - Lausanne - New York - Oxford - Shannon - Tokyo

F re s hwate r and Estuarine Radioe c o k t gy

Edited by G. Desmet et al.

1997 Elsevier Science B.V.267

Distribution of natural radioactivity within an estuaryaffected by releases from the phosphate industry

A. Travesí, C. Gascó, M. Pozuelo, J. Palomares, M.R. Garcíaand L. Pérez del Villar

CIEMAT-IMA. Auda. de la Complutense 22, Madrid 28040, Spaín

ABSTRACT

The distribution and behaviour of the radionuclides 210Pb, "oPo *t¿ 226¡¡¿ in the Odiel

and Tinto river estuaries, southwest Spain, have been studied. This system receives

large quantities of solid and liquid effluents in the form of phosphoglrpsum waste from

the phosphate industry containing natural radionuclides. Ranges of activities from 20

to 5000 Bq kg:l(d.w.) in riverine sediments were obsen¡ed. The ratios of radionuclides

were also determined (uncertainties quoted to 2 o), showing clear disequilibria in the

effluents from the factories (210PbP10pe = 2.7fl.6,2r0PbP26Ra = 0.610 -I,2roPoP26Ra =

0.2410.03) and from the phosphogypsum piles (210PbP10ps = 2.Lfl.6,2roPbP26Ra -

1.510.6, 2LoPo[226Ra = 0.710.2). However, the sampling sites on the rivers affected

directly by the discharges exhibit activity ratios other than those found in the effluents,

manifesting their different behaviour in the estuarine environment. The estimated

inventory in sediments for these radionuclides was 0.92 + 0.20 TBq (1993) which can be

compared with the annual release of 0.52+0.04 TBq (1993) from the phosphogypsum

piles and factories. Preferential deposition of 210Po and 210Pb rather than 226Raonto the

river bed was observed. The proportion of total sediment 210Pb activity associated with

particles less than 2 pm in diameter, which is one of the most resuspendable and

transportable sizes, is 57o-I5Vo.

1. INTRODUCTION

In contrast to the nuclear industry little is known about the discharges and

risks of radionuclides from non-nuclear industries. However, due to the indus-

trial activity of the non-nuclear industry, natural radionuclides can be concen-

trated in the industrial effluents and cause a significant dose to the population.

Due to the large bulk transfer, large quantities of radionuclides are released in

this way to the environment.

268

In Spain, a large phosphate ore processing complex [1] is located at Huelva,close to the estuary formed by the rivers finto and Odiel. The "phosphogyp-

sum" produced as a waste product of the industrial process is, in PaÉ, directlydumped in suspension into the Odiel River near its confluence with the Tintoriver before it reaches the sea. Approximately 8 million cubic meters of liquideffluents are discharged into the Odiel every y€il, containing around 4 x 108Kg of phosphogypsum [1]. The major fraction of phosphorypsum is not directlydumped, but carried out in suspension and deposited over the tidal flats on theeastern side of the Tinto river, forming large deposits of phosphogypsum whichhave resulted in the near total sterility of the tidal flats. These deposits areformed by settling of suspended matter from the discharges in pools createdalong the river which are successively covered by new flows of the suspendedmatter. The overtyrng liquid drains away through fissures, after the depositionof the solids, into the finto river. The gypsum deposits reach a thickness of 4-6m and their total surf,ace covers approximately 4x106 m'. It is estimated that,up to the present, more than 10to I(g of phosphorypsum has been deposited inthis area. Both environmental and radiological impacts produced by thesedikes, were analyzed in previous studies P-4. The environmental impact iscaused by the desertification of the zorre, and the radiological impact by itsproximity to the urban area of Huelva.

The estimation of the dose to the population is done using models thatrequire the determination of the concentration in different components of theecosystem. These models should consider the disequilibrium of natural radio-nuclides after the chemical treatment of the factories and their later releases.

Another fact of significance is the disequilibria among radionuclides belong-ing to the natural radioactive chains that are supposed to be in secular equilibriumin the environment. Some authors reported this fact for certain elements such aspolonium and lead in the estuarine areas [5,6] due to their preferential associationwith the suspended parüicutate matter. Where phosphate factories exist, thesedisequilibria c¿ul be produced by chemical treatment of the raw mineral, whichcontains large quantities of radionuclides in the *'U decay chain [7]. They aredischarged to the aquatic environment, with the radiologically important raüonu-clides 226Ra,, ztopS and "oPo [8]. Ttre largest doses from marine pathways arepredicted for these radionuclides, 210po being the dominant contributor via thepreferential pathway of the consumption of molluscs [9].

Besides increasing the knowledge of the behaviour of natural radionuclidesin estuarine areas, the main objectives of this research were: (a) to analyze the210po,210pb and 2269u distribution in the estuary, focusing the attention on theabiotic part of the ecosystem, and (b) to assess quantitatively the radiologicalconsequences of the aquatic discharges of the phosphate industry.

In this paper, the identification of the source term (releases of the factory), theüstribution of natural raüonuclides within the two rivers, the inventories ofradionuclides in sediments, and the fractionation of activity concentration arepresented.

269

Fig. 1. Sampling stations in the estuary formed by the Odiel and Tinto rivers.

2. IVIATERIALS AT{D METHODS

2.1. Sampling

A sampling network was established on the Odiel and finto rivers. Sixteen

stations were selected; examining the waters and bottom sediments along both

rivers, up-stream from the effluent discharge sites, along the estuary and on

uelva

OCEANO ATT.A¡TTICO

270

the beaches of the Atlantic coast. The sampling stations are shown in Fig. 1.The sediments were collected with a Shipek grab sampler by the University ofSeville in Febmary 1993. The samples were dried at 40"C until constant weightwas achieved, except for those samples used for the determination of granu-lometric composition. In this case the sediments were frozen and stored untiltheir particle size analysis [10].

2.2. Radioanalytical methods

The 210Po was extracted from the sediment after its total dissolution withsequential acid leaching (HNOB, HF, HCI and HCIO4). The polonium was elec-troplated onto a silver disk according to the method of Flynn [11]. The chemicalrecovery was determined by addition of 2o8Po tracer obtaining an average recov-ery of 90Vo. The polonium activities were measured by alpha spectrometryusing silicon surface-barrier detectors.

The radiochemical procedure used to determine 210Pb actiüty is based onthat described in Joshi [12]. The lead leached from the sediment as describedabove. The solution was then passed through an anion-exchange resin (Dowex

1x8 Cl-) A pure lead sulfate precipitate was obtained after various steps ofpurification [13]. "oPb was determined by counting the 1.17 MeV beta emissionof its daughter product "oBi. Yield was calculated gravimetrically with a stabletracer of lead obtaining an average recovery of 90Vo. Also, 210Pb was directlydetermined by its 46.5 KeV gamma peak. The sediments prepared in n geome-try were measured by y-spectrometry, with a low enerry photon planar germa-nium detector. The results obtained for both methods were compared byapplyrng the following statistical analysis between duplicates [14]:

where: S¿ = standard deviation between duplicatesi 4 = difference betweenduplicates divided by the mean of the duplicates. P = number of duplicates.

The results of both ztopS analyses are in good agreement (88Vo), with aconfidence level of 1 o. In the calculation of ratios between radionuclides theradiochemically determined results were used due to their lower uncertainty.

The activity of 2269u was determined by y-spectrometry using a coaxialgermanium detector. The contribution from 235IJ was subtracted from the 185KeV peak activity. The uncertainties are quoted at 2 o.

2.3. Inuentory estimation

The determination of inventory was made using the following formula

I ¡ = A ¿ ' D ¡

27L

where: /¿ = inventory of radionuclide i expressed in Bq m-'; A¿ = concentrationactiüty of radionuclide i expressed in Bq kg-t (dry weight); D¡ = surface densityof sediment expressed in kg m-2.

To calculate the inventories, D¿ was assumed constant along the river, with

an average value (to a depth of 5 cm) of 43 t 16 kg m-t (6 stations).Three areas were identified for the puqposes of this study. The Odiel river,

estimated by the University of Sevilla to have an area of 3 kmz [15,16], wasdivided into four sectors, called A,B,C and D. The areas of the finto river andthe Estuary were both divided into two sectors, called A and B.

2.4. Granulometric analysis of the sediments

For separation of the <2 pm fraction, the dry sample was stirred in distilledwater. The fraction remaining in suspension after 24 hours was then collected.Stokes'|aw was used to show that particles remaining in suspension after this

time are those with a diameter <2 pm. The process was repeated until aquantity of these particles sufficient for analysis was obtained [17].

The particle size distribution of the <62 pm diameter fraction was made

using a Coulter Counter Model TA-II.

3. RESULTS AND DISCUSSION

3.1. Radioactiuity of factory effiuents

The most significant discharges from the phosphate works were the direct

discharges from the factory to the Odiel and the supernatant of phosphogyp-

sum piles outflowing to the Tinto River [18]. The discharge is released by

extracting water from the river and mixing it with the liquid that contains the

acid used in mineral dissolution. The releases are made via a pipe line that is

located at the front of the industrial installation.The activity ratios between the different radionuclides from the discharge

pipes illustrate the disequilibrium existing after the treatment of the phos-

phate minerals.The bulk of the inventory released to the river during the operation of the

factory since it started production cannot be calculated as there is no historical

discharge or effluent radionuclide concentration data. Indeed the frrst records

are from 1988.

3.2. Distribution of radionuclides actiuities on riuerine sediments

The results of "oPb, 2topo and "6Ra concentration activities (1993) along the

river are presented in Table 2. There is a considerable increase in radionuclide

activity close to the discharge point of the effluent pipes (S4, S10) and a

272

Percentage

1 6

1 4

1 2

1 0

E

6

4

2

0

1 6

1 4

1 2

1 0

8

6

4

2

0

1 6

1 4

1 2

1 0

8

6

4

2

0

o/o 1 61 4

1 2

1 0I

6

4

2

0

s-10

s-1 1

o 5.5 6.9 8.6 10.9 13.8 17.4 21.9 27.6 34.7 4d¡.8 55.2 69.s 87

Grain size umFig. 2. Granulometric composition of selected riverine sediments.

decrease of activity in the stations located close to the estuary (S15, 516), asexpected. Theztopbfropo activity ratio upstream (stations 51 and 52) is close tounity as expected in an area not influenced by the discharge. The stationsdownstream of the pipes in both rivers (S3, 54, 55, 56, 57, 58, 59, S10, S13),and close to the estuary (S15, S16), show ztopblztopo activity ratios between 0.36+ 0.27 and 0.86 + 0.05, significantly lower than in the discharge pipe and thephosphorypsum piles (Table 1). This reduction in the activity ratio of theseradionuclides in the riverine sediments can be attributed to their differentgeochemical behaviour. Because "oPo is more easily adsorbed onto the suspended

10.9 13.8 17.4 21.9 27.6 U.7 /|3.8 55.2 69.5

o 5.5 6.9 8.6 10.9 13.8 '�17.4 21.9 27.6 U-7 43-8 55.2 69.5 87

o 5.5 6.9 8.6 10.9 13.8 17.4 21.9 27.6 34.7 43.8 55.2 69.5 87

273

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TABLE 3

Contents o¡210p¡ in the fraction of sediment <2 ¡tm in diameter

Fraction of activity onparticles <2 pm(Vo)

s-4s-6s-10s-11

7.7+0.30.22+0.O21.4510.05o.r2+0.02

t.75.99.23.9

4.810.4L4.65.7

particulate matter than "oPb, this results in a rapid removal of the poloniumand a higher accumulation rate for this element than lead, and consequently ahigher polonium concentration in the sediments and a decrease in theztop6ftopo activity ratio. A similar behaviour c¿rn be observed in the Tagusestuary [19], which is also influenced by the releases of phosphate industries.There is a different ratio of these radionuclides ztop6ftopo (1:2) in the particu-late suspended matter from the Tagus estuary, but unfortunately there is nodata on disequilibria of radionuclides in their effluents after the treatment ofthe phosphate minerals.

The uncertainty in the ztop6fzega activity ratios obtained at some stationsdoes not allow us to determine their different behaviour. At stations 54 (close

to Foret) and S10 (close to phosphogypsum piles), i.e. those directly affected bythe discharges, the2LoPbf26Ra ratios are in good agreement with the ratios inthe effluent (see Table 1).

The enhanced ztopofzaga activity ratios at stations 54 and S10 close to thedischarge points reflect the incremental increase in the concentration of polo-nium in the sediments compared to radium for the reasons given above.

The radionuclide contents in the upstream stations (S1, S2 Odiel river) arehigh if compared with the natural radioactivity of non-polluted Spanish rivers.The natural radionuclide contents of Catalan river sediments r¿rnge from 6 to20 Bq kg-t tttu 120,211 and in the Jarama river they range from L2 to 105 Bqkg-t "tU 1221. Contents from 45 to 138 Bq kg-t {"6Ra) are reported in Tagusriver [23] and 28 to 62 Bq kg:-t {t3tu) and 30 to L24 Bqkg¡t {"oPb) in Frenchrivers [2a]. The existence of old Roman galena mines and the mineralogicalcomposition of the river bed may be the cause of the high ztopS activities(506-922 Bq kg-') at stations 51 and 52.

The activity concentration in the sediment fraction less than 2 pm at selectedstations is shown in Table 3. These stations were selected as representativesof maximum and minimum values of activities. The percentage of activityassociated with the size less than 2 pm was calculated using the followingformula:

Measured activity in 1 g ofsediment particles <2 pm (Bq)

Fraction of bulk sample<2 W(Vo)

F=+276

where: F = fracLton of activity on fine particles; p = fraction of bulk sample <2 ¡tm;C = rri€asured activity in bulk sample; G = measured activity in fraction <2 pm.

As is shown, the fraction of radioactivity present in these particles is

between 5 and L\Vo. This fraction is "theoretically" resuspendable, and can be

transported and collected by the organisms that live in the estuary. This is an

important factor that must be taken into account when models are applied in

the context of radiological hazard.

3.3. Riuerine sediment inuentory

The estimated total inventory of ttoPb, 210po and 226Ra in the sediments ispresented in Tables 4 and 5. The estimated quantity of radionuclides released

during 1993 in the whole area is 0.52 + 0.04 TBq, which is comparable with thetotal inventory in the sediments of 0.92 + 0.20 TBq present during that year. It

TABLE 4

Estimation of radionuclides inventories in sediments from Estuary

Area x Station106 m2

Inventory Bq + 1o

*210p6 21opo 226R^

Odiel riverAB

c

D

2.10lot7.1oe1.10e14.1084.lo1o+1.10102.10ea7.1081.10et5.1081.1010+5.10e2.10e19.1081.101ot4.loet. lo1ot4. loeg.10er3.10e

g.101ot4.lo10

9.10et3.10e

2.1010+6.10e2.10er6.1086.1010t2.1010g.loet1.1oe

3.10e11.10e

2.10e17.108l.101otb.loe1.101ol5. loe9.10et3.10e

2.101116.10102.101019.10e

4.1010+1.10108.1010+3.1010

1.10lotb. loe

4.1010+2.10102.10e18.108

1.101otb.loe2.10e18.1081.1010+4.10e1.1010+4.10e7.10et3.10e

6.101012.1010

2.10lotz. loeg.101o+1.1010

0.590.200.300.200.230.270.2L0.350.360.23

s1-s2s-3s-4s-5s-6s-7s-8s-9s-9s-9

s-10s-11

Tinto riverA 2.4B 2.5

EstuaryA 1.8B 1 .8

s-13 3.101011.1010s-14 5.1010+2.1010

*Radiochemistry values considered of 210Pb'

**Average Surface density expressed in Kg m-2 = 43 (5 cm depth).

277

TABLE 5

Inventory ofthe 210Pb, 210po and 226Ra (5 cm depth) (1993)

Inventory Bq+2o

*Released **Sd *Released **Sd *Released **Sd

Total (TBq)

*Released **Sd

210p5 210po 226R^

2.1011+ 3.1011+B.1o1o 5.1010

8.10lot 4.101h4.10e z.1o1o

0.92+0.20

is worthy of note that errors in the estimation of inventories could have beenmade due to the calculation of the surface area of the river bed (from unknownbathymetry) and the scarce information obtained from the factories (realistic

and controlled information of the volume released is needed). However, a betterestimate of the total inventory could be made if the sedimentation rate of the

area was known and core sampling to a depth of 50 cm was made. This is one

of the objectives of further research in the area.

4. CONCLUSIONS

The radiological impact of phosphate factories on the environment is easily

detectable in the area of Huelva estuary. Higher levels of natural radioactivity

are observed in the rivers Tinto and Odiel than in others not affected by suchindustries (ten to fifteen times the content of a non-polluted Spanish river).

The releases of 0.5 TBq from the factories are preferentially transferred tothe river-bed which has a present inventory approximately 1 TBq for the threeradionuclides considered in this study.

The 2lopoftoPb, zzagu/zropb and zzeg¿ztopo activity ratios manifest üsequili-bria in the natural radioactive series after the acid treatment of the mineral

and as a consequence of differential behaviour in the estuarine ecosystem.The particles less than 2 mm in diameter contain a small percentage of

radionuclides (5-L5Vo), but this has to be considered in models of radiologicalhazard assessment as this is the fraction which is easily resuspended andtransported.

5. ACKNOWLEDGEMENTS

The authors would like to thank the University of Sevilla (Department of

Nuclear Physics) for collaboration in this project and in the sampling campaigll.

They would also thank the Agencia del Medio Ambiente Andaluzfor technical

3.1011+2.1010

2.101h3.1010

0.52-0.04

278

assistance and the use of sampling equipment. They would like to mention the

excellent analytical work performed by F. Palomares. This work was partially

funded by the Radiation Protection Research Programme of the European

Union (contract no. FISP-CT-0035 "Pathways of radionuclides emitted by nonnuclear industries") and by ENRESA (Empresa Nacional de Residuos Radiac-tivos S.A of Spain).

6. REFERENCES

1. La Industria Química y Básica en Huelva, 1989. Libro blanco. Huelva.Z. Josa-García, J.M., 1980. Procesos para la separación y recuperación del uranio del

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