Radiation Dosimetry of Small Mammals Inhabiting a Liquid Radioactive Waste Disposal Area

Abstract

Radiation doses received by small mammals inhabiting a dry radioactive leaching pond on the Idaho National Engineering Laboratory Site in southeastern Idaho were determined by surgically implanting lithium fluoride thermoluminescent dosimeter (TLD) chips. One hundred eight—two TLD packets were implanted in 3 species; white—footed deer mouse (Peromyscus maniculatus), least chipmunk (Eutamias minimus), and Ord's kangaroo rat (Dipodomys ordii), with 65% recovery. All species from the radioactive leaching pond received significantly greater (P <.001) doses than control species. The deer mice received a mean dose equivalent rate of 160 mrem/day which was significantly greater (P <.001) than the mean dose equivalent rates received by least chipmunks (17 mrem/day) and Ord's kangaroo rats (6 mrem/day). The mean dose received by deer mice was 8% of the maximum air exposure recorded near the ground surface of the leaching pond. The maximum dose rate received by an individual deer mouse was nearly 50% of the maximum exposure rates in the study plot. Interspecific dose differences appeared to be related to habitat preference. Deer mice were most frequently captured on the gravelly and sparsely vegetated dry pond bed which had site exposure rates of 200 to 2000 mRoentgen/day. Conversely, chipmunks and kangaroo rats were usually captured on the pond banks which were adjacent to areas with sandy soil and denser vegetation. Site exposure rates on the pond banks ranged from 10 to 30 mRoentgen/day. Doses received by individuals of each species had high variation which appeared to be caused by the variable air exposure rates and the mobility of the small mammals. Intraspecific differences in activity, behavior and home range may have also influenced the dose variability in individual rodents. The advantage of implanted TLD over externally attached TLD and possible radiation effects on small mammal populations are discussed.