Distribution of radionuclides in mussels, winkles and prawns. Part 1. Study of organisms under environmental conditions using conventional radio-analytical techniques

Abstract

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 α-emitting ( 210Po, 238Pu, 239 + 240Pu, 241Am) and γ-emitting ( 95Nb, 95Zr, 103Ru, 106Ru, 137Cs, 241Am) radionuclides in their tissues and organs. Ravenglass mussels exhibited 239 + 240Pu concentrations ranging from 43 Bq kg −1 dry in muscle tissue to 1658 Bq kg −1 dry in byssal threads, the corresponding 137Cs range being 131–1340 Bq kg −1. Although 210Po 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 137Cs, 210Po and 239 + 240Pu in the total soft parts of Ravenglass mussels were, respectively, 9, 25 800 and 1400. In Cumbrian winkles, nuclide concentrations ranged for 239 + 240Pu, from 18·5 Bq kg −1 dry (muscle tissue) to 457 Bq kg −1 dry (pallial complex); for 137Cs, from 103 (foot tissue) to 1495 Bq kg −1 (pallial complex) and for 210Po, from 12·2 (muscle tissue) to 145 Bq kg −1 (digestive gland). Total soft part concentration factors (CFs) were calculated to be 16 for 137Cs, 5500 for 210Po and 5700 for 239 + 240Pu. 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 γ-emitter activities were present above detection limits and the highest 239 + 240Pu concentration was 5·96 Bq kg −1 dry in the carapace. 210Po 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 × 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 210Po are higher than those from 239 + 240Pu in mussels but are less than those from 239 + 240Pu in winkles.