Abstract
As one of the studies on the aspect of water pollution of the Lake Kasumigaura, the second largest lake in Japan, the accumulation and the distribution of the fission products, in the lake, which were originated from the past nuclear tests were investigated.
The Sr-90 concentrations in the lake are 0.8 pCi/l in water, 230 pCi/kg in the dried sediments, 5-100 pCi/kg in living fish and shellfish. The concentrations of Cs-137 are 0.2 pCi/l in water, 2 × 103 pCi/kg in the dried sediments and 10-60 pCi/kg in living fish or shellfish. The areal distribution of Sr-90 in sediments is uniform all over the Lake. However, Cs-137 concentration in the bottom sediments of the near shore is lower than that in the center of Lake. The vertical distribution of both nuclides in the sediments of the central bottom are shown as follows.
(1) Sr-90 concentrations in the layer from 0 to 30 cm in depth and Cs-137 concentrations from 0 to 20 cm are higher. The concentrations of both nuclides are highest in the range of 10 to 15 cm.
(2) Sr-90 concentrations in the layer between 30 and 45 cm in depth and Cs-137 concentrations between 20 and 25 cm are intermediate.
(3) Sr-90 concentrations in the layer deeper than 45 cm and Cs-137 deeper than 25 cm are very low.
