Contribution of animal experimental data for the risk assessment of exposure to radon decay products

摘要

Experimental studies were used in addition to epidemiological studies to investigate the effects of exposure, exposure rates and other factors in predicting risks resulting from human exposures. The advantage of data from animals is that animals can be exposed under carefully controlled conditions and that exposure and exposure rate can be estimated more accurately. This review summarises data on lung cancer risk from radon experimental studies focusing on the exposure-rate effects. A dose-effect relationship was established in rats, which was very similar for medium and high cumulative exposures, to that observed in uranium miners. At high cumulative exposures up to 3000 WLM (10.8 J hm~(-3)), an inverse dose-rate effect similar to that observed in uranium miners was also found in rats. In contrast, recent results from our group indicate that at relatively low cumulative exposures of 0.36 Jhm~(-3)(100 WLM), comparable to lifetime exposures in high-radon houses or current underground mining exposures, the risk of lung cancer in rats decreases with PAEC, i.e., exposure rate. This confirms the results obtained at lower cumulative exposure, showing that for a similar cumulative exposure of 25 WLM (0.09 Jhm~(-3)), the relative risk (RR) of lung cancer decreases with decreasing exposure rates. These data suggest that the induction of lung cancer results from a complex interplay between cumulative exposure and exposure rate, with an optimal combination of these two parameters, i.e., a combination of cumulative dose and dose rate that results in a maximum risk of lung cancer induction. They support the hypothesis that, at low doses, the risk of lung cancer is governed by the rate at which the dose is delivered, and not by the total cumulative dose alone. These data are also consistent with that of underground uranium miners showing an inverse dose-rate effect at high cumulative exposures, but a diminution of this effect at cumulative exposures lower than 50 WLM (0.18 Jhm~(-3)). They support both an inverse dose-rate effect at high cumulative exposures, as well as its diminution or disappearance at low cumulative exposures.