Effects of 90Sr on Tree Swallow Nestlings Near Groundwater Contaminant Plumes

Discharge of groundwater contaminant plumes has created elevated concentrations of Sr-90 in some aquatic sediments at Chalk River Laboratories. Tree swallows (Tachycenita bicolor) feed and supply their nestlings almost exclusively with airborne insects that developed as larvae in aquatic sediments. To monitor the uptake and test for potential detriment due to Sr-90 in a terrestrial animal, we measured the gross beta concentrations in the bone of 12-d-old tree swallow nestlings in areas having sediments with elevated levels of gross beta (Sr-90 and Y-90) and in several control areas where sediment gross beta was primarily due to naturally occurring K-40. Nesting behavior and reproductive success of the tree swallows were similar regardless of the gross beta concentrations in sediments near their nest boxes. Radiation can damage DNA and cause micronuclei to form in cells, so we examined the frequency of micronuclei in erythrocytes of nestlings. The formation of micronuclei in the erythrocytes of the nestlings was also similar wherever nestlings were analyzed. The results revealed no significant increases even near sediments with the highest gross beta levels. At Perch Lake, where Chalk River Laboratories has a large area of Sr-90-contaminated sediments, the bones of 12-d-old nestlings contained gross beta concentrations as high as 29 Bq g(-1). This would produce a skeletal dose rate of 9 mu Gy h(-1), which is one-fourth of the threshold dose rate of 40 mu Gy h(-1), above which detriment could occur. Failing to find any indication of detriment in the field study, we irradiated wild eggs in the lab and returned them to their nest for natural incubation, hatching, and feeding by the parents. There was an increase in formation of micronuclei following a dose of 3.2 Gy, and the other results were consistent with existing literature.