CO-CARCINOGENIC EFFECTS IN RATS OF COMBINED EXPOSURE TO RADON AND OZONE

The aim of this study was to estimate in rats the potential carcinogen ic or co-carcinogenic risk of ozone, acting either alone as a complete carcinogen, or as a promoter after pulmonary irradiation by inhalatio n of radon and its decay products. Three experimental groups were used : Group 1 was exposed to radon and daughters at a cumulative exposure of 3.6 J h m(-3) (1000 WLM); Group 2 was exposed first to radon in the same conditions as Group 1, and one month after the end of radon expo sure, to ozone by inhalation at a concentration of 0.2 mu L L-1, 6 h d (-1), 5 d/week for 6 months; Group 3 was exposed to ozone alone in the same conditions as Group 2. The incidence of lung cancer was 16% in G roup 1, 24% in Group 2, and 4% in Group 3, compared with 0.8% in contr ols. Lung carcinomas induced by ozone alone showed a trend toward a pr eferential differentiation pattern to the squamous cell type. These re sults show a direct carcinogenic effect of ozone in rats for levels of exposure in the same range as those observed during peak levels of ur ban airborne pollution and suggest a potential co-carcinogenic effect of combined exposure to radon and ozone. Copyright (C) 1996 Elsevier S cience Ltd.