AN EXPERIMENTAL-STUDY ON THE BIOACCUMULATION AND TURNOVER OF PO-210 AND PB-210 IN MARINE SHRIMP

The experimental accumulation of Po-210 and Pb-210 from seawater alone and from seawater and food was studied in the laboratory with the benthic shrimp Lysmata seticaudata. Shrimp accumulated both radionuclides from water for 21 d, reaching whole body concentration factors [CF = (Bq g-1 of shrimp wet wt)/(Bq ml-1 filtered water)] of 139 +/- 28 for Po-210 and 682 +/- 149 for Pb-210. 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 Po-210 in internal tissues which was not accompanied by an identical accumulation of Pb-210. It is concluded that in shrimp Po-210 was mainly accumulated from food, whereas Pb-210 was largely taken up from the fraction dissolved in seawater. A much higher digestive assimilation efficiency for Po-210, about 5-fold that of Pb-210, was observed in L. seticaudata. This difference can account for the enhancement of Po-210:Pb-210 ratios observed in the lower trophic levels of marine food chains. Turnover of Po-210 in shrimp tissues is much slower than for Pb-210, a fact which also contributes to the enhanced Po-210:Pb-210 concentration ratios observed in marine crustaceans.