A MORTALITY KINETICS APPROACH TO CHARACTERIZING THE FRACTIONATED EXPOSURE-MORTALITY RESPONSE RELATIONSHIP OF RADON PROGENY

The utility of mortality kinetics analysis in evaluating mortality dat a from fractionated exposure studies was demonstrated using radon-prog eny induced extra mortality as an example. Gompertz (log-hazard) funct ions were used to characterize the mortality of male SPF Wistar rats e xposed to radon progeny at 100 WL and 1000 WL for total exposures rang ing from 20 to 10 240 WLM. There was an upward parallel displacement o f the Gompertz functions following the period of radon exposure. The s hape of the Gompertz functions for the exposed animals was consistent with a Gompertz model of toxicity resulting from short-term exposure, resulting in non-repaired injury that summates with natural (aging) in jury. The parallel upward displacements (epsilon(ss)) of the Gompertz functions showed an unexpected non-monotonic pattern for rats exposed at 1000 WL. The parallel upward displacements showed a sharp upward in crease from 320 to 640 WLM, fell at 1280 WLM, and thereafter increased linearly to 10 240 WLM. These data suggest that the radon progeny exp osure-mortality response is non-linear. In contrast, there was no sign ificant parallel upward displacement of the Gompertz functions for rat s exposed at 100 WL for total exposures of 20-1280 WLM, but a large di splacement began at 2560 WLM total exposure.