The experimental accumulation of 210Po and 'lOPb from seawater alone and from seawater and food was studied in the laboratory with the benthic shrimp Lysrnata seticaudata. Shrimp accumulated both radionuclides from water for 21 d, reaching whole body concentration factors [CF = (Bq g-' of shrimp wet wt)/(Bq ml-' filtered water)] of 139 k 28 for "OPo and 682 + 149 for 'l0Pb. When uptake was from water only, tissue analyses revealed that radionuclide accumulation was mainly due to external adsorption. Accumulation in internal tissues also occured through the intake of seawater for osmotic regulation. Exposure of shrimp to radionuclides dissolved In water and labelled food produced a noticeable accumulation of 210Po in internal tissues which was not accompanied by an identical accumulation of 210Pb. It is concluded that in shrimp 210Po was mainly accumulated from food, whereas 210Pb was largely taken up from the fraction dissolved in seawater. A much higher digestive assimilation efficiency for 210Po, about 5-fold that of ''Opb, was observed in L. seticaudata. This difference can account for the enhancement of 2'oPo:210Pb ratios observed in the lower trophic levels of marine food chains. Turnover of 2'0Po in shnmp tissues is much slower than for 2'0Pb, a fact which also contributes to the enhanced 2'o~o:2'0Pb concentration ratios observed in marine crustaceans.

Accumulatlon of polonium In the common prawn Palaemon serratus and the sea perch Serranus scnba was studied expenmentally to clanfy the relative Importance of water and food as sources of the hlgh 210Po concentrations usually found in marlne organisms A double-tracer technlque was used whlch enables dlfferentlating the bioaccun~ulation of PO dissolved in seawater (as 210Po) and the dlgestlve transfer of PO from food (as 208Po) Accumulatlon of d~ssolved PO by prawns was found to occur m a~n l y through adsorption on the exoskeleton w~t h a minor accumulation in internal tissues through the intake of seawater for osmoregulatlon In contrast, 208Po in labelled food was r e a d~l y absorbed and accumulated In the Internal tlssues of prawns Sim~lar expenments w~t h fish indicated that "'PO dissolved in seawater did not contribute directly to PO accumulated in lnternal organs Instead, nearly all internally bound PO resulted from the assimilat~on of 208Po-labelled food Measured PO absorption efficlenc~es were approxmately 0 35 and 0 05 of the Ingested dose for prawns and flsh respect~vely, and roughly corresponded to the assimllatlon effic~encies of proteins from food In both pra\vns and flsh, ingested 208Po distributed In the tissues In a manner s~m~l a r to naturally occurnng 'I0Po in control organlsms, whereas 2'oPo dissolved in seawater parhhoned differently Modelling uptake through both pathways demonstrated that PO in the food accounted for >97 % of the PO measured in these 2 organlsms These expenmental results suggested that, In nature, accumulation of PO by m a n n e organlsms In higher trophlc levels depends upon the prevlous PO blndlng to organlc matter In lower troph~c levels, therefore, PO transfer through manne food-chains is p n m a r~l y a funct~on of the food a s s d a t~o n effic~ency and feeding rate of the organlsms The double-tracer technlque descnbed here IS a useful expenmental tool in the study of PO transfer pathways in manne organisms, and could also be a p p l~e d to the study of other aspects of PO b~ogeochenl~stry

No abstract

The experimental accumulation of 210Po and 'lOPb from seawater alone and from seawater and food was studied in the laboratory with the benthic shrimp Lysrnata seticaudata. Shrimp accumulated both radionuclides from water for 21 d, reaching whole body concentration factors [CF = (Bq g-' of shrimp wet wt)/(Bq ml-' filtered water)] of 139 k 28 for "OPo and 682 + 149 for 'l0Pb. When uptake was from water only, tissue analyses revealed that radionuclide accumulation was mainly due to external adsorption. Accumulation in internal tissues also occured through the intake of seawater for osmotic regulation. Exposure of shrimp to radionuclides dissolved In water and labelled food produced a noticeable accumulation of 210Po in internal tissues which was not accompanied by an identical accumulation of 210Pb. It is concluded that in shrimp 210Po was mainly accumulated from food, whereas 210Pb was largely taken up from the fraction dissolved in seawater. A much higher digestive assimilation efficiency for 210Po, about 5-fold that of ''Opb, was observed in L. seticaudata. This difference can account for the enhancement of 2'oPo:210Pb ratios observed in the lower trophic levels of marine food chains. Turnover of 2'0Po in shnmp tissues is much slower than for 2'0Pb, a fact which also contributes to the enhanced 2'o~o:2'0Pb concentration ratios observed in marine crustaceans.

No abstract