CARCINOGENIC AND COCARCINOGENIC EFFECTS OF RADON AND RADON DAUGHTERS IN RATS

It has been previously established that lung cancer could be induced i n rats by exposure to radon and radon daughters. Although the oat-cell carcinomas that are common:in humans were not found in rats, other hi stological types of lung carcinomas, especially squamous cell carcinom as and primitive lung adenocarcinomas, were similar to those observed in humans. A dose-effect relationship was established for cumulative d oses: varying from 25 to 3000 working-level-months (WLM), which was si milar for medium and high cumulative doses to that,: observed in urani um miners. This experimental protocol was also used to study the poten tial cocarcinogenic effects of Other :: environmental or industrial ai rborne pollutants such as tobacco smoke, mineral fibers, diesel exhaus ts, or minerals from metallic mine ores that may act synergistically w ith radon exposure. In rats exposed to radon and tobacco smoke combine d, the incidence of lung cancers was higher by a factor-of 2-4 accordi ng to the cumulative radon exposure and the duration of tobacco smoke exposure. When mineral fibers were injected intrapleurally, an increas ed incidence of malignant thoracic tumors was observed in rats exposed to radon and fibers combined, but synergistic effects resulted in add itivity. With diesel exhausts or minerals from metallic ores, a slight , nonsignificant increase in the incidence of lung carcinomas was obse rved compared with rats exposed to radon alone. These results demonstr ated that iris possible to establish the potential cocarcinogenic acti on, showing either multiplicative, additive, or no effect of various e nvironmental or industrial airborne pollutants combined with radon exp osure. This radon model is valid for investigating possible interactio ns between two occupational exposures.