Effect of liming on the behaviour of (90)Sr and (137)Cs in a lake ecosystem.

Liming of lakes is considered one possible remedial action to reduce the accumulation of radionuclides into fish in the case of a radiological accident. These responses were tested in field conditions in a small acidified lake that was divided into two parts: one limed with CaCO(3) and the other half left as an unlimed control. The transfer of (90)Sr from water into fish decreased on average by 50% during the first year after liming. However, at the same time the (90)Sr concentration in water increased, reaching a maximum within 6 months after liming. Approximately 50% more (90)Sr was detected in water in the limed part of the lake than on control side during the first year. (90)Sr was most probably released from the sediment as the Ca concentration and pH of the water increased. As a result of these two processes, which counterbalanced each other (increased release of (90)Sr into water from sediment and decreased transfer of (90)Sr from water into fish), the (90)Sr concentration in fish did not notably differ between the limed and control sides of the lake. Liming may only be suitable as a remedial action if carried out immediately after a radiological accident, before significant amounts of radionuclides have been deposited in lake sediments. In the case of (137)Cs, the effect of liming was less pronounced. (137)Cs activity concentration in water increased in the first year by 20% and uptake by fish decreased by 20%.