Investigation of cancer epidemiology and study of carcinogenic agents in the Shanghai Rubber Industry

Preliminary studies on crude cancer incidences among workers from 89 factories in Shanghai revealed excessive risk of cancer for workers in certain workshops of rubber tire factories. Chronic in situ animal exposures showed that compounding and Banbury mills for mastication and mixing were origins of carcinogenic contaminants. Various chronic experiments indicated the carcinogenicity of PBNA in rats and mice, especially with regard to the lungs. The high concentration of PBNA in the atmosphere of the work area seemed to be related to the excessive incidence of lung cancer among the workers. Epidemiological investigation showed that there was an excessive number of cases of lung cancer in the workshop of rubber tire factories where compounding, mixing, and milling took place.

Carcinogenicity of N-phenyl-1-naphthylamine and N-phenyl-2-naphthylamine in mice

Technical N-phenyl-1-naphthylamine ( PANA ), which is an optic isomer of N-phenyl-2-naphthylamine ( PBNA ), has been used as a rubber additive without suspicion of its being carcinogenic. When male ICR mice were given repeated s.c. injections of both technical and pure PANA in dimethyl sulfoxide, it resulted in high percentage of malignant tumors similar to that in mice given technical PBNA . PANA had a tendency to induce hemangiosarcoma. Similar injections of PANA and PBNA into male TA-1 mice gave similar results. Previous unilateral nephrectomy enhanced both PANA and PBNA induction of renal hemangiosarcomas. The similar carcinogenic potency of PANA and PBNA suggests other routes of metabolic activation besides dephenylation for both chemicals in mice.