Uptake and depuration of 131I by the edible periwinkle Littorina littorea: uptake from seawater

Uptake and depuration experiments for the edible periwinkle Littorina littorea have been performed using 131I-labelled seawater. Throughout the experimental phase the winkles were fed on unlabelled Chondrus crispus. 131I concentrations in winkles during uptake followed linear first-order kinetics with an uptake half-time of 11 days, whereas for depuration a triphasic sequence with biological half-lives of 4, 23 and 56 days was determined. In general, iodine turnover in winkles via labelled seawater appears to be slower than observed for other molluscs (2–3 days). Most of the activity prior to and after depuration is found to be in the shell, with indications that shell and soft parts accumulate and depurate 131I at a similar rate. The operculum displays the highest specific activity of all fractions with a concentration factor of 750 l kg−1. Concentration factors for whole winkle, shell, soft parts and digestive gland are in the order of 40–60 l kg−1, higher than the IAEA recommended CF value for iodine in molluscs of 10 l kg−1. The 131I CF in winkles is closer to that of the conservative radionuclides 99Tc and 137Cs than the CF of the particle reactive radionuclides 239,240Pu and 241Am.