Accumulation of Co-60 and Cs-134 in lake whitefish in a Canadian Shield lake

Radionuclides were added to the anaerobic hypolimnion of a Canadian Shield lake during the summer of 1989 to simulate nuclear fuel waste leakage into the bottom waters of a lake with deep groundwater flow. Lake whitefish (Cor egonus clupeaformis) were sampled in mid-October each year from 1989 to 199 4, except for 1992, to determine the concentration of Co-60 and Cs-134 in t heir tissues. The radionuclides remained in the hypolimnion until lake mixi ng in the autumn. Subsequently, there was more loss of Co-60 than Cs-134 fr om the water. After one year, 4% of the Co-60 and 15% of the Cs-134 remaine d in the water. This decreased to about 0.4% of the Co-60 and 0.6% of the C s-134 in the water after five years. Little Co-60 and Cs-134 were present i n lake whitefish the first autumn following the radionuclide addition. In f ish, the highest concentrations were recorded in October, 1990, after which concentrations gradually decreased. Cobalt-60 concentrations were lower th an Cs-134 concentrations, probably because Co-60 has a high affinity for or ganic particles and was not available for uptake. The relatively high Cs-13 4 concentrations in fish reflects its tendency to remain in the water and i ts continued availability to biota. Both Co-60 and Cs-134 concentrations we re high in the soft tissues. Co-60 was mainly distributed in the flesh, gut , gill, kidney, and liver, whereas Cs-134 was mainly distributed in the fle sh. The occurrence of relatively high Cs-134 concentrations in lake whitefi sh five years after their addition to the lake, long after Cs-134 concentra tions are no longer detectable in lake water, attests to the continued pers istence of this contaminant in aquatic biota.