1927 Environmental Toxicology and Chemistry, Vol. 20, No. 9, pp. 1927–1935, 2001  2001 SETAC Printed in the USA 0730-7268/01 $9.00 + .00 Environmental Toxicology ACCUMULATION OF 137 CESIUM AND 90 STRONTIUM FROM ABIOTIC AND BIOTIC SOURCES IN RODENTS AT CHORNOBYL, UKRAINE RONALD K. CHESSER,*²‡ B RENDA E. RODGERS,§ JEFFREY K. WICKLIFFE,§ SERGEI GASCHAK,‡ IGOR CHIZHEVSKY,‡ CARLETON J. PHILLIPS,§ and ROBERT J. BAKER‡§ ²Department of Genetics, University of Georgia, Athens, Georgia 30602, USA ‡International Radioecology Laboratory, Slavutych, Ukraine §Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409, USA ( Received 19 July 2000; Accepted 21 December 2000) Abstract—Bank voles (Clethrionomys glareolus) and laboratory strains of house mice (Mus musculus BALB and C57BL) were relocated into enclosures in a highly contaminated area of the Red Forest near the Chornobyl (Ukraine) Reactor 4 to evaluate the uptake rates of 137 Cs and 90 Sr from abiotic sources. Mice were provided with uncontaminated food supplies, ensuring that uptake of radionuclides was through soil ingestion, inhalation, or water. Mice were sampled before introduction and were reanalyzed every 10 d for 137 Cs uptake. Levels of 90 Sr were assessed in subsamples from the native populations and in experimental animals at the termination of the study. Uptake rates in house mice were greater than those in voles for both 137 Cs and 90 Sr. Daily uptake rates in house mice were estimated at 2.72  10 12 unstable atoms per gram (whole body) for 137 Cs and 4.04  10 10 unstable atoms per gram for 90 Sr. Comparable rates in voles were 2.26  10 11 unstable atoms per gram for 137 Cs and 1.94  10 10 unstable atoms per gram for 90 Sr. By comparing values from voles in the enclosures to those from wild voles caught within 50 m of the enclosures, it was estimated that only 8.5% of 137 Cs was incorporated from abiotic sources, leaving 91.5% being incorporated by uptake from biotic materials. The fraction of 90 Sr uptake from abiotic sources was at least 66.7% (and was probably much higher). Accumulated whole-body doses during the enclosure periods were estimated as 174 mGy from intramuscular 137 Cs and 68 mGy by skeletal 90 Sr in house mice over 40 d and 98 mGy from 137 Cs and 19 mGy from 90 Sr in voles over 30 d. Thus, uptake of radionuclides from abiotic materials in the Red Forest at Chornobyl is an important source of internal contamination. Keywords—Radiation Chornobyl Chernobyl Dose Rodents INTRODUCTION The explosion and subsequent fire at the Chornobyl nuclear facility on April 26 through May 6, 1986, resulted in the at- mospheric dispersion of vast quantities of highly radioactive particulate matter [1]. Approximately three to six exobec- querels (EBq) were released into the environment [2,3] and distributed across eastern and northern Europe [4]. Complex particles associated with the nuclear fuel inventory of Reactor 4, however, were scattered into the habitats immediately sur- rounding the reactor facility [5]. In the regions of the Red Forest and Glyboke Lake (Ukraine), heavy depositions of ra- dioactive ash on trees and water bodies resulted in the death of more than 400 ha of pine forest [6]. Presently, less than 2% of the radionuclide activity originally released by the Chor- nobyl accident remains. The remaining fraction is comprised of dangerous levels of 137 Cs and 90 Sr, which have considerable biological affinity and long half-lives (30.1 and 28.2 years, respectively). Physical and chemical transformation of the radionuclide material has led to the incorporation of high concentrations of 137 Cs and 90 Sr into the biota within the exclusion zone, which is an area with a 30-km radius around the Chornobyl nuclear power plant [7]. Small mammals from the Red Forest, ap- proximately 2 km west/southwest of Reactor 4, averaged more than 13,000 nuclear disintegrations per second (Becquerels [Bq]) of 137 Cs in each gram of muscle tissue. This activity results in an average dose rate of almost 10 mGy/d (1 mGy * To whom correspondence may be addressed (rchesser@ttu.edu). = 0.1 rad), or 10-fold the maximum guidelines established by the International Atomic Energy Agency (Vienna, Austria) [8]. Although sterility resulting from chronic doses of 1 mGy/d or more has been reported [8,9], no evidence has been found for reproductive inhibition in mammals from the Red Forest [7,10,11]. In fact, the density of mammals in the exclusion zone is comparable to that in areas with relatively low radio- active contamination only 30 km from the reactor [12]. In previous studies of native rodent species, the bank vole (Cleth- rionomys glareolus) consistently showed the highest specific activity of intramuscular 137 Cs, averaging almost 25 kBq/g, which yields a dose rate of approximately 18 mGy/d [7,13]. The primary route for incorporation of radionuclides into the mammals inhabiting the Chornobyl exclusion zone likely is biotic transfer. Radiocesium is a biological analogue of po- tassium, whereas radiostrontium is an analogue of calcium. Concentrations of radionuclides remain substantially higher in the soils and sediments (i.e., abiotic concentrations) than the concentrations that are transferred into the biotic community. Thus, 137 Cs and 90 Sr will be absorbed from the soil through plant root systems and incorporated into cells, and ingestion of plant material will convey radioactive material to herbi- vores. Typically, 137 Cs and 90 Sr in the biotic portion of a con- taminated ecosystem will be less than 1% of that in the abiotic fraction [14–16]. Small mammals often construct underground burrows and nests and, therefore, surely ingest and inhale soil particles containing radionuclides. Clearly, uptake of free par- ticulate matter by inhalation, drinking, and ingestion of soils may be an important avenue for loading mammalian tissues with radionuclides. The potential for ingestion of soil deposited