Chronic Toxicity and Carcinogenicity Studies of 1-Methylnaphthalene in B6C3F1 Mice

The carcinogenic potential of 1-methylnaphthalene (1-MN), acompound which exists widely in the environment, was investigatedin B6C3F1 mice. Groups of 50 male and 50 female mice were givendiets containing 0, 0.075, or 0.15% 1-MN for 81 weeks. Bothtreatment groups developed pulmonary alveolar proteinosis athigh incidence, with 46.0 and 34.7% of females and 46.0 and38.0% of males, respectively, being affected. Total lipid andphospholipid levels in sera and monocytes in peripheral bloodwere also significantly increased in 1-MN-treated female andmale mice in contrast with control values. The incidences ofbronchiolar/alveolar adenomas in the lungs of male mice givenboth 0.075 or 0.15% 1-MN were 26.0 and 24.0%, respectively,in both cases significantly increased in contrast with the 4.1%observed for control males. However, neither dose dependencenor significant difference in the incidences of bronchiolar/alveolarcarcinomas between 1-MN-treated and control male mice was observed.The incidences of other tumors also were similar in both 1-MN-treatedand control groups. The results of the present experiment thussuggested a possible weak carcinogenic potential of 1-MN tothe lung of male but not female B6C3F1 mice.