A double-tracer technique to determine the relative importance of water and food as sources of polonium-210 to marine prawns and fish

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 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 KEY WORDS: Natural radioactivity .Polon~um .