Concentrations and Dose Rate Estimates of super(134,137)Cesium and super(90)Strontium in Small Mammals at Chornobyl, Ukraine

Free-ranging mammals near the Chornobyl nuclear reactor are experiencing substantial radiation dose rates from intramuscular concentrations of super(134,137)Cs and skeletal super(90)Sr. Radiocesium concentrations averaged 3,200 Bq/g of dry muscle, compared to a mean of 297 Bq super(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 super(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 mu 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 super(90)Sr for taxa among sites was significantly less than that for super(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.