Biological Fate of Cobalt-60 Released During the Corrosion of Neutron-Activated Stanless Steel in Seawater

摘要

Passing seawater over radioactive Type 347 stainless steel in a sediment/seawater laboratory system and exposing marine animals to this environment provided information on the bioaccumulation of exp 60 Co from radioactive structural material. Exposure of marine organisms to radioactive corrosion products and directly to radioactive stainless steel in seawater simulated some of the possible conditions which could arise from the deposition of radioactive stainless steel on the ocean floor. Detectable levels of exp 60 Co in marine animals were not observed on a short term basis (5 weeks). Longterm (13 months) exposure of marine animals in a sediment/seawater system resulted in exp 60 Co bioaccumulation. The specific activity of exp 60 Co in the organisms was as much as one million times less than that initially present in the radioactive stainless steel. This was due to the dilution of exp 60 Co by stable cobalt in the seawater, sediments and organisms. As expected the exp 60 Co specific activity of the organisms never increased above that of the radioactive source. This is because exp 60 Co is chemicaly indistinguishable from stable Co. Increasing exp 60 Co concentration factors with decreasing exp 60 Co concentrations in the seawater and sediment media coupled with relatively constant exp 60 Co specific activities suggest a possible homeostatic control of cobalt concentrations in certain marine organisms. The evidence indicates that the marine animals derived more of the accumulated exp 60 Co from the sediments and interstitial water than from seawater. Cobalt-60 concentration factors were generally found to be lower than published cobalt concentration factors due to the predominantly insoluble nature of the corrosion products. Baseline information is provided on trace element concentrations in deep-sea organisms. Stable Co and twenty other elements were measured in abyssal invertebrates and a fish. (ERA citation 07:044746)