Specific cesium activity in freshwater fish and the size effect.

The specific Cs-137 activity of muscle tissue of silver carp (Hypophthalmichthys molitrix) from the cooling pond of the Chernobyl nuclear power plant caught in 1987 and 1988 increased almost linearly with fish weight ("size effect") in contrast to liver tissue, whose specific activity remained independent of weight. A kinetic model for uptake and excretion was developed to describe the size effect in muscle tissue by introducing a weight-dependent Cs biological half-time to fish. Similar size effects of specific Cs-137 activity were also found for other species of fish from the cooling pond, but were primarily attributed to changes in feeding habits with increasing weight of fish rather than to metabolic changes, since the specific Cs-137 activity both of muscle and liver tissue increased with fish weight for those species in contrast to silver carp.