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Toxicology of 85Kr: chronic exposure studies.

Male and female Wistar rats were exposed chronically to graded doses of 85Kr to determine long-term biological effects of simulated environmental exposure. Rats were exposed in 4 groups, including room air-exposed controls and 3 groups exposed to 85Kr concentrations equivalent to 10(2), 10(3) and 10(4) times the maximum permissible concentration (MPC) for the general population (3 X 10(-7) microCi/ml). Exposures continued 24 hr/day, 7 days/week for 808 days, until only approximately 10% of the original 400 rats were alive. No effect of 85Kr exposure was observed on weight gain or tumor incidence, including leukemias. The results support the adequacy of established 85Kr exposure limits for the general population in light of the absence of evidence of build-up in tissues after chronic exposure and the lack of exposure-related biological effects in rats after near-lifespan exposure to concentrations equivalent to 10,000 times the MPC.