Uptake of americium-241 from two experimentally labelled deep-sea sediments by three benthic species: a bivalve mollusc, a polychaete and an isopod

Abstract

Laboratory experiments were conducted to determine the bioavailability of 241Am in contaminated deep-sea sediments to 3 benthic organisms: the bivalve mollusc Venerupis decussata. the polychaete Hermione hystrjx and the isopod Cirolana borealis. The biological availability was determined in 2 different sediments: the 'Atlantic sediment', originating from the NEA dumpsite in the NE Atlantic and the 'Pacific sediment', originating from a seabed disposal feasib~lityin vestigation site in the Pacific Ocean. The affinlty of 2 4 1 ~fmor the sediments was very high: K, values amounted to 1.5 X 105 + 3.0 X 104 for the Atlantic and 1.8 X 105 + 2.0 X 104 for the Pacific sediment. Accumulation of the radionuclide by the 3 species, measured over a period of 40 to 50 d, yielded transfer factors (TF = radioactivity g-' animal wet weight/radioactivity g-' wet sediment) lower than unity. Uptake of 2 4 1 ~wma s highest in the polychaete (TF Pacific = 0.12; TF Atlantic = 0.05). whereas radionuclide accumulation in the isopod (TF Pacific = 0.032; TF Atlantic = 0.006) was comparable with uptake by the bivalve (TF Pacific = 0.02; TF Atlantic = 0.004). Most of the radionuclide in the clam (56 to 75 %) was fixed to the shell; 78 % to 96 % of the 24%m was fixed to the body wall of the polychaete. The relative distribution of the radionuclide among the animals' tissues did not vary with the sediment type, whereas transfer factors in shell and viscera of clams and body wall of worms were dependent upon sediment type. In all cases transfer factors were up to 2 to 5 times higher for animals in Pacific sediment, although Kd's in both sediments were not statistically different. 241Am K, values in these sediments were found to be insensitive indicators of relative bioavailability of the radionuclide; however, the different geochemical associations of 241Arn in both sediments (in particular a highly resistant fraction not removed by hot acid leaching) can be used to explain the observed differences in bioavailability.