Uptake and elimination of radiocaesium in fish and the "size effect.".

A number of hypotheses have previously been developed concerning the rates of uptake and elimination of radiocaesium (137Cs) in fish. These include the influence of potassium and other water chemical parameters on both uptake and elimination, and the effect of fish size on accumulation. In order to test these hypotheses, we have assembled a data set comprising more than 1,000 measurements of radiocaesium (137Cs) in predatory fish (perch, pike and brown trout) in nine European lakes during the years after Chernobyl. These data have been analysed using simple models for uptake and excretion of 137Cs in fish, showing that: 1. Fish-water concentration factors (CF) were inversely proportional to potassium [K+] concentration of the different lakes, in agreement with previous studies. 2. The uptake rate of 137Cs in fish was negatively correlated with lake [K+], but excretion rate was independent of [K+]. 3. Lower than expected CF values were found in one lake, Iso Valkjärvi, Finland. This is attributed to inhibition of the K+ (and therefore 137Cs) high affinity transport system in aquatic plants and fish by low pH and/or low Ca2+. 4. The inclusion of fish weight as a parameter in our dynamic model significantly improves the ability of the model to fit the observed measurements of 137Cs. 5. The model developed from the above hypotheses was able to fit the data from nine different lakes to within approximately a factor of 3 of the observed values.

Model testing using Chernobyl data: II. Assessment of the consequences of the radioactive contamination of the Chernobyl Nuclear Power Plant cooling pond.

The "Cooling Pond" scenario is designed to test models for radioactive contamination of aquatic ecosystems, based on data for contamination of different aquatic media and biota due to fallout of radionuclides into the cooling pond of the Chernobyl Nuclear Power Plant. Input data include characteristics of the cooling pond ecosystem (hydrological, hydrochemical, and hydrobiological conditions) and estimates of the amounts of 137Cs in the cooling pond. Predictions are requested in two stages: (1) calculations for 137Cs concentrations for comparison against actual measurements, including activities of 137Cs in the cooling pond water, in sediment layers, and in fish; and (2) calculations for which actual measurements are not available, including dose and risk estimates for aquatic biota and for humans following hypothetical consumption of contaminated biota. The latter calculations are intended to provide an opportunity for intercomparison among modelers of their results for a simulated assessment problem.

Using a bank of predatory fish samples for bioindication of radioactive contamination of aquatic food chains in the area affected by the Chernobyl accident.

From the analysis of experimental data on radioactive contamination of various fish, it is suggested that predatory fish specimens can be used as bioindicators of radionuclide accumulation in reservoir food chains of the Chernobyl emergency area. The increased content of cesium radionuclides were detected in the muscle tissue of predatory fish collected in various regions of the Chernobyl emergency area. In most of the water bodies studied, maximum contamination levels of predatory fish by radionuclides of cesium occurred in 1987-1988, whereas in 'nonpredatory' fish the concentration of cesium was maximum, as a rule, in the first year following the accident. The exposure doses of fish of various ecological groups and ages are estimated. The exposure doses of various population groups, using fish from contaminated water bodies, are also estimated. When forming the environmental data bank for the Chernobyl accident zone it is suggested that perch, pike-perch and pike be used as bioindicators of radioactive contamination of food chains.

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.