Concentrations and dose rate estimates of (134,137)cesium and (90)strontium in small mammals at Chornobyl, Ukraine

Free-ranging mammals near the Chornobyl nuclear reactor are experiencing su bstantial radiation dose rates from intramuscular concentrations of Cs-134, Cs-137 and skeletal Sr-90. Radiocesium concentrations averaged 3,200 Bq/g o f dry muscle, compared to a mean of 297 Bq Sr-90/g in bone for mammals in t he Exclusion Zone, a region of restricted human activity surrounding the re actor. Estimates of dose rates from intramuscular sources of radiocesium av eraged 2.4 mGy/d within 8 km of the reactor and ranged as high as 60 mGy/d. Overall dose rates from internal Sr-90 for mammals in the Exclusion Zone a veraged 1.0 mGy/d, although doses to specific tissues are likely much highe r. Mammals captured 30 km southeast of the reactor averaged only 2 Bq/g of muscle and were receiving an average of 1.4 mu Gy/d from internal radiocesi um. Dramatic Variation exists in the spatial pattern of radiocesium in area s immediately surrounding the reactor and within and between remediated and unremediated regions. The variance of Sr-90 for taxa among sites was signi ficantly less than that for Cs-134,Cs-137. Thermoluminescent dosimeters pla ced on free-ranging mice showed that dose rates from external sources of ra diation were much greater than the dose rates from internal sources of radi ocesium. Estimated dose rates in very small areas of the Chornobyl region e xceed those reported to impede reproductive success in mammals.