Abstract-Free-ranging mammals near the Chornobyl nuclear reactor are experiencing substantial radiation dose rates from intramuscular concentrations of 134,137 Cs and skeletal 90 Sr. Radiocesium concentrations averaged 3,200 Bq/g of dry muscle, compared to a mean of 297 Bq 90 Sr/g in bone for mammals in the Exclusion Zone, a region of restricted human activity surrounding the reactor. Estimates of dose rates from intramuscular sources of radiocesium averaged 2.4 mGy/d within 8 km of the reactor and ranged as high as 60 mGy/d. Overall dose rates from internal 90 Sr for mammals in the Exclusion Zone averaged 1.0 mGy/d, although doses to specific tissues are likely much higher. Mammals captured 30 km southeast of the reactor averaged only 2 Bq/g of muscle and were receiving an average of 1.4 Gy/d from internal radiocesium. Dramatic variation exists in the spatial pattern of radiocesium in areas immediately surrounding the reactor and within and between remediated and unremediated regions. The variance of 90 Sr for taxa among sites was significantly less than that for 134,137 Cs. Thermoluminescent dosimeters placed on free-ranging mice showed that dose rates from external sources of radiation were much greater than the dose rates from internal sources of radiocesium. Estimated dose rates in very small areas of the Chornobyl region exceed those reported to impede reproductive success in mammals.

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An empirical two compartment model is presented which describes the transfer of radiocesium from fallout contaminated lichen to reindeer. Kinetic parameters were calculated from data derived from retention studies following a single dose of 134Cs to reindeer maintained on a natural mountain tundra pasture at Cantwell, Alaska. Cesium retention values were statistically indistinguishable for the autumn and winter period, however cesium retention half-times were reduced 2-4 fold during the summer months as compared to the autumn-winter studies. Cesium kinetics in the reindeer were not influenced significantly by animal sex although a significant increase in cesium retention with animal weight was observed. Results obtained from controlled lichen feeding experiments indicated that about 20-30% of the radiocesium contaminating lichen is available for absorption by the reindeer.The model was tested by comparing predicted values with results obtained with a single reindeer maintained on a constant 134Cs intake. Predicted values are compared to observed radiocesium concentrations in the lichen-caribou segment of the Arctic food chain.