Effect of liming on the behaviour of 90Sr and 137Cs 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 CaCO3 and the other half left as an unlimed control. The transfer of 90Sr from water into fish decreased on average by 50% during the first year after liming. However, at the same time the 90Sr concentration in water increased, reaching a maximum within 6 months after liming. Approximately 50% more 90Sr was detected in water in the limed part of the lake than on control side during the first year. 90Sr 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 90Sr into water from sediment and decreased transfer of 90Sr from water into fish), the 90Sr 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 137Cs, the effect of liming was less pronounced. 137Cs activity concentration in water increased in the first year by 20% and uptake by fish decreased by 20%.

► Acidified lake was divided into two parts: one limed with CaCO3 and the other half left as an unlimed control.
► The transfer of 90Sr from water into fish decreased by 50% during the first year after liming.
► At the same time liming increased the 90Sr concentration in the water by 50%.
► The increased amount of 90Sr in water is assumed to have originated from the lake sediments.
► The 90Sr concentration in fish remained relatively unchanged.