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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.

Wistar rats were exposed to 85Kr gas atmospheres to determine saturation/desaturation kinetics in major tissues. Tissue partition coefficients [concentration 85Kr in tissue (muCi/g)/concentration of 85Kr in the atmosphere (muCi/cc)] were determined following equilibration with 85Kr gas. Tissue partition coefficients were highest for adrenals and fat; lowest for bone, heart and brain. Tissue partition coefficients for immature rats, 1-12 days of age, and for adults, were not significantly different. The highest concentrations of 85Kr were found in fatty tissues and in gas pockets in the intestinal lumen.