Laryngeal cancer incidence among workers exposed to acid mists (United States).

In 1992, the International Agency for Research on Cancer (IARC) determined that sufficient evidence existed to classify sulfuric acid mists as a human carcinogen, based primarily on six human studies. Possible mechanisms include irritation of epithelial cells in conjunction with cigarette smoking, or a direct genotoxic effect due to a modification of cellular pH. We have followed 1,031 men exposed to acid mists in the steel industry in the United States, via mailed questionnaire and telephone interview, extending by 10 years a prior follow-up of this cohort. These workers averaged 9.2 years of exposure, with an average first year of exposure of 1949. The primary exposure was to sulfuric acid mist, although part of the cohort was exposed to other acid mists. Fourteen laryngeal cancers were observed in the cohort compared with 5.6 expected based on US rates, with follow-up through 1994. A 14 percent upward adjustment in expected cancers due to differences in tobacco and alcohol consumption led to 6.4 laryngeal cancers expected, yielding a rate ratio of 2.2 (95 percent confidence interval = 1.2-3.7). Our findings are consistent with previous findings from this cohort and from most other studies, and tend to confirm IARC's classification of acid mists as a human carcinogen. The occupational exposures of this cohort were at least an order of magnitude higher than usual ambient exposures in urban air.