210Pb enhancement in rivers affected by the phosphate rock processing in southwestern Spain

21ºPb enhancemen in i e s a ec ed by he phospha e ock p ocessing in sou hwes e n Spain A. Ma ínez-Agui e and M. Ga cía-León Facul ad de Física, Uni e sidad de Se illa, Apdo. 1065, 41080 Se illa, Spain ABSTRACT The ac i i y le els o 21ºPb in solu ion and bo om sedimen a we e measu ed in he es ua y o med by he Odiel and Tin o i e a in sou hwes Spain. The le els in bo h wa e and sedimen samples indica e ha he discha ges om wo e ilize ac o ies in he a ea enhance he adioac i i y o such samples. l. INTRODUCTION Recen ly, high adioac i i y le els o U, Th and 226Ra iso opes we e ound in solu ion, suspended ma e and bo om sedimen s o he Odiel and Tin o i e s loca ed in sou hwes em Spain [l-3]. The anomaly was a ibu ed o wo e il ize ac o ies loca ed in an indus ial complex su ounded by hese wo i e s (Fig. 1). These ac o ies elease hei was es di ec ly o he Odiel i e o s o e hem in unco e ed piles nea he Tin o i e channel. In his pape , we ha e ex ended p e ious wo k o he s udy o 210Pb in solu ion and bo om sedimen s. 2. SAMPLES AND EXPERIMENTAL METHODS Se en poin s on he Odiel i e , ou on he Tin o i e and one a he con lu ence o bo h i e s (Fig. 1) we e sampled o wa e and bo om sedimen s in July 1990 (d y season) and in Feb ua y 1991 (we season) o e alua e seasonal a ia ions in 21ºPb ac i i ies. The pH o he wa e s was measu ed a he ime o sampling. The suspended ma e was sepa a ed by il a ion h ough Nu cleopo e il e s o 0.45 µm po e size. Immedia ely, he il a e was acidi ied o pH -2 wi h concen a ed HNOa, The small size ac ion (d < 63 µm) was sepa a ed om sedimen samples in o de o de e mine he 21ºPb con en . De e mina ions o pe cen o ganic ma e and pe cen o wa e we e ca ied ou on each bo om sedimen sample. N � PHOSPHOGYPSUM PILES 0 FERTILIZER INDUSTRIES o 3km Fig. l. Map o he Odiel and Tin o i e s which shows he sampling s a ions along bo h i e channels. The e ilize ac o ies and he phosphogypsum s o age a ea a e also shown. 21ºPb was de e mined h ough he measu emen o i s daugh e 21ºPo by cx-spec ome y, a le secula equilib ium was achie ed. The samples we e spiked wi h known ac i i ies o 208Po o de e mine he chemical eco e y o he o al p ocedu e. Samples we e i s acid diges ed wi h concen a ed HN08 ollowed by aqua egia and, inally dissol ed in 8 M HN08• Po was sepa a ed using a sol en ex ac ion me hod wi h TBP as he o ganic phase and 8 M HN03 as he ino ganic phase. A e igo ous shaking Po emains in he ino ganic phase whe eas o he adionuclides join he o ganic phase. The solu ion con aining he Po was e apo a ed o d yness and sel deposi ion o Po on o sil e planche s was encou aged by shaking gen ly a 60ºC. The planche was inally measu ed by cx-spec ome y wi h ion implan ed de ec o s. Fu he de ails on he adiochemical p ocedu e a e p esen ed in Mo ón e al. [ 4). 3. RESULTS AND DISCUSSION To simpli y he subsequen discussion we will i s p esen he esul s o wa e samples om bo h i e s o all sampling campaign.s, ollowed by hose ob ained o bo om sedimen s. Samples O ep esen hose alcen in he Odiel i e , T in he Tin o i e and OT in he con luence o bo h i e s. Sedimen samples a e iden i ied as SO, ST and SOT o he Odiel, Tin o and he con lu ence espec i ely. The index ep esen s he sampling s a ion along each i e (Fig. 1). 3.1. Wa e s The esul s ob ained o he analysis o 210Pb in wa e samples alcen du ing he low ide in 1990 (d y season) and 1991 (we season) a e p esen ed in Table l. The le els o 21ºPb in he Odiel i e a ea unde s udy ange om 3. 7 ± 0.5 o 289 ± 22 mBq 1-1 wi h he maxima, in summe and in win e , in on o one o he e ilize ou alls (Fig. 2). The le els dec ease quickly downs eam om his poin , due, p obably, o p ecipi a ion o Fe and Mn du ing mixing downs eam [5]. This ac i i y pa e n is simila o hose ob ained p e iously o o he adionuclides [1,2) e lec ing he p esence o a local sou ce o adioac i i y ( he e ilize indus ies) along he i e channel. The minimum le els ound in sum me a e clea ly highe han hose in win e , p obably due o a lowe wa e s eam low o he i e in he d y season. In he case o he Tin o i e he le els along he channel a e qui e cons an , anging om 17.0 ± 1.5 o 26.6 ± 3.0 mBq 1-1 in summe 1991, wi h a sligh dec ease downs eam o he channel. In 1991, he le els ange om 15.3 ± 3.1 o 45.6 ± 2.7 mBq 1-1• In bo h campaigns he TABLE I Da a o 21ºPb in mBq 1-1 in wa e samples (low ide) aken om he Odie! and Tin o i e basins in 1990 (d y season) and 1991 (we season). The pH o he wa e s a he ime o sampling is also gi en. N.M means no measu ed 1990 1991 Code pH 210pb pH 210pb 01 2.86 21.1±2.5 3.90 N.M. 02 6.37 7.9±1.0 5.52 7.8±0.7 03 6.42 10.2±3.4 5.90 3.7±0.5 04 6.35 289±22 5.96 36.4±2.6 05 6.32 34.4±2.2 6.03 8.4±0.8 06 6.48 12.2±1.4 6.06 7.4±1.1 07 6.40 14.0±1.0 6.02 50.6±3.9 Tl 2.41 41.7±3.1 2.88 N.M. T2 5.54 26.6±3.0 3.22 45.6±2.7 T3 5.82 19.5±1.5 5.56 15.3±3.1 T4 6.10 17.0±1.5 6.40 30.7±5.7 OT 6.56 11.7±1.0 6.23 10.5±1.2 º' Odlel and Tin o wo e s 02 03 04 05 06 07 ----1990 - - -- --1991 OT T4 T3 T2 T1 Fig. 2. 210pb in mBq 1-1 in wa e samples aken om he Odiel and Tin o i e s in 1990 and 1991. maximum le el in he Tin o i e was ound in s a ion T2. This s a ion is loca ed close o an a i icial s eam coming om he · phosphogypsum s o age a ea. In ac , he pH o he wa e a his s a ion is lowe han a he es o he s a ions, a 3.22 in 1991 (Table 1), which e lec s he was es eleased a his poin . We also obse e ha he le el o 210Pb ound a s a ion T4 o he Tin o i e is qui e simila o ha ound a s a ion 07 o he Odiel i e . This ac could be explained by he in luence ha con amina ed wa e s om he Odiel i e ha e on he Tin o i e channel. Thus, con amina ed wa e om he Odiel i e can low ups eam in o he Tin o i e when he ide changes om low o high. In he Ne he lands, Kos e e al. [6] ob ained le els o 210Pb o 0.9 mBq 1-1 in wa e s o he Oos e chelde sys em while in he a ea a ound a e ilize ac o y in he Nieuwe Wa e weg sys em hey ound 10 mBq 1-1. In gene al, he au ho s assumed le els below 1 mBq 1-1 as a backg ound le el, hose highe han 3 mBq 1-1 as p obably enhanced and inally, hose highe han 5 mBq 1-1 as clea ly enhanced. Lewis [5] epo ed dissol ed 21ºPb in no mal i e wa e s o be less han 0.2 mBq 1-1• By con as in acid i e wa e s, dissol ed 210Pb was ound o each 230 mBq 1-1 in he Colo ado sys em and 2.8 mBq i-1 in he wes b anch o he Susquehannah i e [7]. Compa ing he le els o 21ºPb in he Odiel and Tin o i e s o bo h sampling campaigns we should conside bo h i e s o be clea ly enhanced in 210Pb ac i i y by he e ilize indus ies, pa icula ly in he a ea close o he ou alls. The backg ound le el away om he ou alls appea s o be a ound 7 mBq 1-1• We will conside sepa a ely he case o samples 01 and Tl, which we e collec ed a he sou ce o bo h i e s, a om he e ilize indus ies (20 km ups eam in bo h cases) and una ec ed by hei was es. Bo h sampling s a ions p esen le els o 210Pb much highe han he usual alues in esh i e wa e s. This ac mus be ela ed wi h he acid pH o he wa e s (Table 1) a bo h s a ions. These acid pHs p oduce a dissolu ion o 210Pb om soil pa icles and consequen ly a highe 21ºPb ac i i y in solu ion, as was p e iously ound in he Colo ado i e and in he Susquehannah i e (6, 7]. This e ec o dissolu ion om bo om sedimen s by he acid pH o he wa e s was also ound o o he adionuclides in he same sampling s a ions (1-3). 3.2. Sedimen s The small size ac ion (d::;; 63 µm) o 7 bo om sedimen s om he Odiel i e , 4 om he Tin o and 1 om he con luence o bo h i e s sampled in 1990 and 1991 we e sepa a ed o 210Pb de e mina ions. The esul s ob ained oge he wi h pe cen o wa e and pe cen o o ganics o each sedimen sample a e p esen ed in Table 2. Le els o 21ºPb a e qui e high in he a ea close o he e ilize indus ies in he Odiel i e , wi h a maximum le el o 799 ± 48 mBq g-1 in 1990 and 534 ± 25 mBq g-1 in 1991. These le els o adioac i i y a s a ions 04 o 07 a e much highe han he backg ound le el, ::;;100 mBq g-1 epo ed elsewhe e [6]. Only in wo s a ions (Fig. 3), ups eam om he indus ies, in bo h sampling campaigns, does he le el o 210Pb all in he non enhanced ange (::;;100 mBq g-1). 210Pb ac i i y le els a s a ion 07 we e much lowe (::;;100 mBq g-1) in he 1990 TABLE2 Da a o 210Pb in mBq g-1 in he small size ac ions o bo om sedimen a aken om he Odie! and Tin o i e basins in 1990 (d y season) and 1991 (we season). Pe cen o wa e and pe cen o o ganice in he sedimen samples a e siso gi en. N.M. means no measu ed Code %Wa e % O ganics 210pb %Wa e % O ganice 210pb S01 52.58 5.73 N.M. 61.18 15.40 N.M. S02 26.64 11.76 13.9±1.3 24.53 3.09 8.0±0.7 S03 60.58 9.51 27.2±1.5 57.21 8.25 40.9±2.7 S04 52.53 10.91 212±10 39.13 11.57 284±14 S05 65.51 5.26 438±21 59.83 9.74 420±31 S06 58.18 9.47 799±49 67.93 12.95 534±25 S07 65.35 9.47 78.6±3.7 55.64 9.58 411±24 STl 79.63 8.38 N.M. 39.80 2.25 N.M. ST2 38.78 4.34 96.7±6.1 51.37 8.96 33.1±3.3 ST3 59.29 9.64 39.8±1.9 56.8 11.72 233±9 ST4 61.46 8.64 74.4±4.8 56.03 10.93 47.9±2.5 OT 64.98 8.69 149±11 66.77 11.49 204±16 Odlel and Tin a 1edlmen 1 502 503 504 S011 508 507 ___ 1990 ------1991 se S 4 5 3 S 2 Fig. 3. 21°Fb in mBq g-1 in bo om sedimen samples aken om he Odiel and Tin o i e s in 1990 and 1991. sampling campaign han in ha o 1991. This mus be ela ed o so ne d ainage ac i i ies ca ied ou in he a ea in 1990. In he Tin o i e he le els ange om 33.1 ± 3.3 o 233 ± 9 mBq g-1 in he ine ac ion o bo h yea s. 21ºPb le els in he Tin o i e sedimen s, o he same sampling campaigns, a e much lowe han in he Odiel i e . Mo eo e , he e is a clea peak o ac i i y in s a ion T3 in he sampling campaign o 1991 (Fig. 3), wi h le els much highe han he ypical backg ound le el. This s a ion is loca ed a he con luence wi h a small na u al s eam, Es e o del Rincón, (Fig. 1) which c osses he phosphogypsum s o age a ea, and could anspo so ne gypsum pa icles wi h high ac i i y le els. These pa icles will e en ually be deposi ed on he Tin o i e bed a he con luence. High ac i i y le els o o he na u al adionuclides we e also ound a he same s a ion in 1988 and 1989 [1,2]. The s a ions ups eam om he indus ies a he Odiel i e and also s a ions ST2 and ST4 o he Tin o i e , howe e , p esen le els o 21ºPb much lowe and simila o he backg ound le el (SlOO mBq g-1). In gene al, no co ela ions be ween 210Pb con en and o ganic o g anula composi ion we e ound in ei he i e , and he ac i i y pa ems ob ained a e simila o hose ound o o he adionuclides in p e ious yea s [1,2]. 4. ACKNOWLEDGEMENTS The au ho s wish o hank J.M. Ab il, G. Manjon and J. Diaz o helping in he sampling. The wo k was pa ially suppo ed unde con ac DGICYT PB89- 0621 and EEC con ac FI3P-CT920035. 5. REFERENCES l. Ma ínez-Agui e, A. and M. Ga cía-León, 1991. Na u al adioac i i y enhance men by human ac i i ies in i e s o he sou hwes o Spain. J. Radioanal. Nucl. Chem. Le ., 155: 97-106. 2. Ma ínez-Agui e, A., M. Ga cía-León and M. l ano ich, 1994. The dis ibu ion o U, Th and 226Ra de i ed om he phospha e e ilize indus ies on an es ua ine sys em in sou hwes Spaín. J. En i on. Radioac i i y, 22: 155-177. 3. Ma ínez-Agui e, A., M. Ga cía-León and M. I ano ich, 1994. U and Th dis ibu ion in solu ion and suspended ma e om i e s a ec ed by he phospha e ock p ocessing in sou hwes e n Spain. Nucl. Ins um. Me h. Phys. Res. A, 339: 287- 293. 4. Mo ón, M.C., A. Ma ínez-Agui e and M. Ga cía-León, 1988. De e mina ion and le els o U, Th and Po om di e en en i onmen al samples. In: In e na ional Con e ence on En i onmen al Radioac i i y in he Medi e anean A ea. SNE ENS, Ba celona, p. 111. 5. Lewis, D.M., 1977. The use o 210Po as a hea y me al ace in he Susquehanna i e sys em. Geo. Cosmochim. Ac a, 41: 1557. 6. Kos e , H.W., P.A. Ma wi z, G.W. Be ge , A.W. Wee s, P. Van Hegel and J. Niewuenwize, 1991. 210Po, 210Pb and 226Ra in aqua ic ecosys ems and polde s, an h opogenic sou ces, dis ibu ion and enhanced adia ion doses in he Ne he  lands. In: V In e na ional Symposium on he Na u al Radia ion En i onmen , Salzbu g, Aus ia. 7. Sco , M.C., 1982. The chemis y o U and Th se ies nuclides in i e s. In: M. l ano ich and R.S. 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