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

Publisher Website
Google Scholar
Abstract
Laboratory experiments were conducted to determine the bioavailability of 241Am in contaminated deep-sea sediments to 3 benthic organisms: the bivalve mollusk Venerupis decussata, the polychaete Hermione hystrix 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 [Northeast] Atlantic and the Pacific sediment, originating from a seabed disposal feasibility investigation site in the Pacific Ocean. The affinity of 241Am for the sediments was high: Kd values amounted to 1.5 .times. 105 .+-. 3.0 .times. 104 for the Atlantic and 1.8 .times. 105 .+-. 2.0 .times. 104 for the Pacific sediment. Accumulation of the radionuclide by the 3 spp., measured over 40-50 days, yielded transfer factors (TF = radioactivity/g animal wet radioactivity per g wet sediment) lower than unity. Uptake of 241Am was highest in the polychaete (TF Pacific = 0.12; TF Atlantic = 0.05); 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 (56-75%) was fixed to the shell; 78-96% of the 241Am was fixed to the body wall of the polychaete. The relative distribution of the radionuclide among the animals'' tissues did not vary with sediment type; transfer factors in shell and viscera of clams and body wall of worms depended on sediment type. In all cases transfer factors were up to 2- to 5-fold higher for animals in Pacific sediment, although Kd in both sediments were not statistically different. 241Am Kd values in these sediments were insensitive indicators of relative bioavailability of the radionuclde; the different geochemical associations of 241Am 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.