ACCUMULATION, RELEASE, AND TISSUE DISTRIBUTION OF AG-110M FROM NATURAL FOOD (GAMMARUS-PULEX) BY THE COMMON CARP, CYPRINUS-CAPPIO L

Ag-110m uptake from food, retention, elimination, and tissue distribut ion were investigated in the freshwater fish Cyprinus carpio. The expe riments were carried out on two groups of 10 juvenile carps fed, for 8 weeks, with living Ag-110m-labelled gammarids. The fish in the first group, intended for radionuclide accumulation study, were placed in se parate aquaria and received daily, from Monday to Friday, 8-16 prey. T o monitor the Ag-110m uptake kinetics and calculate radioecological pa rameters, radioactivity measurements were performed on the fish once a week on Monday morning just before feeding; the measurements were tak en after 65 h without food, to avoid inclusion of any undigested Ag-11 0m in the digestive tract or in unexcreted feces. The fish in the seco nd group were placed together in an aquarium, fed contaminated gammari ds for 8 weeks, and dissected to evaluate the Ag-110m tissue distribut ion. Immediately following the exposure period, the fish of the first group were transferred into a single aquarium and fed uncontaminated f ood to study radionuclide release. After 7 weeks, the individuals were dissected to determine the tissue distribution of the residual Ag-110 m. Ag-110m accumulation from food by carp can be described by a one-co mpartment exponential model. Consumption of contaminated gammarids res ulted in a radionuclide transfer factor of 23 x 10(-3) at the end of t he 8-week uptake phase. During this phase, the retention factor decrea sed exponentially from 36 x 10(-3) to 16 x 10(-3). A single-compartmen t exponential model was fitted to the Ag-110m elimination data. The co rresponding radionuclide half-life was relatively short (22 days) and after 49 days the fish retained only about 21% of the accumulated Ag-1 10m. Because of biological dilution, due to fish weight gain, the conc entration of the residual Ag-110m was 11.6% of its initial value. Tiss ue distribution study showed Ag-110m accumulation and retention by the liver and digestive tract to be high. Although they represent only ab out 10% of the fish body mass, these two organs accounted for 60-80% o f the total radionuclide body load.