Influence of dose-rate on lung cancer induction in rats exposed to radon and its progeny

Abstract

Background: Experimental animal studies were used in addition to epidemiological studies to investigate the effects of exposure, exposure rate and other factors in predicting risks resulting from human radon exposures. An excess risk of lung cancers was observed in rats at cumulative exposure as low as 0.09 J h m −3 (25 WLM) performed at relatively high potential alpha energy concentration (PAEC) of about 2.1 mJ m −3 (100 WL). A trend toward increased tumour risk with decreased exposure rate was observed in rats exposed at cumulative exposures varying from about 0.72 J h m −3 (200 WLM) up to 10.8 J h m −3 (3000 WLM), and high exposure rates varying from 0.09 J h m −3 (25 WLM per week) to 1.8 J h m −3 (500 WLM per week). In contrast, the results obtained at low cumulative exposure, comparable to domestic indoor exposure showed no evidence of an inverse exposure-rate effect. Methods: A new series of experiments were carried out to investigate specifically the influence of exposure rate on lung cancer induction in rats at relatively low cumulative exposures of about 0.36 J h m −3 (100 WLM), and at potential alpha energy concentrations ranging from 0.27 mJ m −3 (13 WL) up to 3.15 mJ m −3 (150 WL). Results: The results indicate that at relatively low cumulative exposures comparable to lifetime exposures in high-radon houses or current underground mining exposures, the risk of lung cancer in rats decreases with decreasing PAEC, i.e., exposure rates. Conclusion: These data suggest that the induction of lung cancer results from a complex interplay between cumulative and exposure rate, with an optimal combination of these two parameters.