DISTRIBUTION OF RADIONUCLIDES IN MUSSELS, WINKLES AND PRAWNS .1. STUDY OF ORGANISMS UNDER ENVIRONMENTAL-CONDITIONS USING CONVENTIONAL RADIO-ANALYTICAL TECHNIQUES

Mussels (Mytilus edulis) and winkles (Littorina littorea), collected from Ravenglass, Cumbria, England in the vicinity of the British Nuclear Fuels plc nuclear reprocessing plant at Sellafield, and prawns (Palaemon serratus), landed nearby at Whitehaven, have been investigated to determine the distributions of alpha-emitting (Po-210, Pu-238, Pu-239 + 240, Am-241) and gamma-emitting (Nb-95, Zr-95, Ru-103, Ru-106, Cs-137, Am-241) radionuclides in their tissues and organs. Ravenglass mussels exhibited Pu-239 + 240 concentrations ranging from 43 Bq kg-1 dry in muscle tissue to 1658 Bq kg-1 dry in byssal threads, the corresponding Cs-137 range being 131-1340 Bq kg-1. Although Po-210 concentrations were not determined in byssal threads, muscle tissue still displayed the lowest polonium concentration (124 Bq kg-1), whilst the viscera (containing digestive gland, stomach and kidneys) contained the highest (596 Bq kg-1). Subsequent concentration factor estimates for Cs-137, Po-210 and Pu-239 + 240 in the total soft parts of Ravenglass mussels were, respectively, 9, 25 800 and 1400. In Cumbrian winkles, nuclide concentrations ranged for Pu-239 + 240, from 18.5 Bq kg-1 dry (muscle tissue) to 45 7 Bq kg-1 dry (pallial complex); for Cs-137, from 103 (foot tissue) to 1495 Bq kg-1 (pallial complex) and for Po-210, from 12.2 (muscle tissue) to 145 Bq kg-1 (digestive gland). Total soft part concentration factors (CFs) were calculated to be 16 for Cs-137, 5500 for Po-210 and 5 700 for Pu-239 + 240. The magnitude of these CFs, as for those in the mussel, is consistent with the respective CF values recommended by the International Atomic Energy Agency for molluscs. Radionuclide concentrations in Whitehaven-landed prawns were much lower than those observed in mussels or winkles; no artificial gamma-emitter activities were present above detection limits and the highest Pu-239 + 240 concentration was 5.96 Bq kg-1 dry in the carapace. Po-210 activities, however, were more readily detectable throughout the prawn's tissues, concentrations ranging from 2.7 Bq kg-1 (abdomen muscle) to 144 Bq kg-1 (cardiac foregut), producing CFs of the order of 2 X 10(4) in tissues associated with feeding and digestion. Previous studies have attempted to determine the principal nuclide source to marine organisms by comparing nuclide activity ratios in their tissues, sea water and,particulate material From the environmental samples studied here, no single transport medium appears to dominate uptake. The primary radiological implication of the observed radionuclide concentrations in Ravenglass mussels and winkles is that, from seafood ingestion, the critical group receives only a small percentage (ca 10%) of the ICRP-recommended subsidiary dose limit. Dose contributions from Po-210 are higher than those from Pu-239 + 240 in mussels but are less than those from Pu-239 + 240 in winkles.