Chlorothalonil is a broad spectrum, non-systemic fungicide widely used to control diseases affecting over 50 fruit, vegetable and agricultural crops. Despite its extensive use for over 30 years, little is known about the potential human carcinogenicity associated with the routine application of chlorothalonil. Rodent studies have shown evidence of renal tubular carcinomas and adenomas. We explored cancer incidence with chlorothalonil exposure using data from the Agricultural Health Study, a prospective cohort of licensed pesticide applicators in Iowa and North Carolina.
Licensed private and commercial pesticide applicators were recruited into this study from 1993 to 1997. Detailed information regarding pesticide use was obtained via self-administered questionnaires. Cancer incidence was followed through December 31, 2004. Chlorothalonil exposure was classified by lifetime exposure days and intensity-weighted lifetime exposure days, and then categorized into tertiles. The intensity-weighted lifetime exposure days metric was calculated based on a complex algorithm which includes pesticide application methods among other factors. This may increase or decrease exposure.
Of the 47,625 pesticide applicators included in this analysis, 3,657 applicators reported using chlorothalonil with a median of 3.5 application days per year. Chlorothalonil was not associated with overall cancer incidence, nor did we find any association with colon, lung, and prostate cancers – the only cancers for which we had sufficient numbers to explore associations.
We did not find any strong evidence for an association between chlorothalonil and the cancers investigated. Although animal studies have suggested renal cancer may be associated with chlorothalonil, we had insufficient data to evaluate this cancer.