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

Abstract A number of hypotheses have previously been developed concerning the rates of uptake and elimination of radiocaesium ( 137 Cs) 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 1000 measurements of radiocaesium ( 137 Cs) 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 137 Cs 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 137 Cs 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 Valkjarvi, Finland. This is attributed to inhibition of the K + (and therefore 137 Cs) high affinity transport system in aquatic plants and fish by low pH and/or low Ca 2+ . 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 137 Cs. 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.