Pendimethalin exposure and cancer risk among pesticide applicators: a report from the U.S.-based agricultural health study

Purpose We evaluated the incidence of cancer in relation to pendimethalin exposure among pesticide applicators in the Agricultural Health Study, a prospective cohort study of licensed pesticide applicators in Iowa and North Carolina. Pendimethalin is a widely used herbicide, intended for the control of most annual grasses and certain broadleaf weeds in most crops. Methods This study includes 9089 pendimethalin-exposed and 26,836 nonexposed pesticide applicators. At the time of enrollment (1993–1997), detailed information on pesticide exposure and potential confounders was obtained from a self-administered questionnaire. Poisson regression analysis was used to evaluate the effect of pendimethalin exposure, categorized into tertiles, on cancer incidence, controlling for the effects of potential confounding factors. Results Significant increased relative risks (RRs) for rectum cancer among subjects with the highest life-time pendimethalin exposure days were observed compared with both non-pendimethalin-exposed (RR = 3.5, 95% CI = 1.3–9.2) and low-pendimethalin-exposed (RR = 9.2, 95% CI = 1.1–81.1) applicators. We also observed an increased RR for rectum cancer when we used intensity-weighted lifetime pendimethalin exposure days as the exposure metric, using non-pendimethalin-exposed applicators as the referent group (RR = 3.5, 95% CI = 1.3–9.2, Ptrend = 0.04). Relative risk for lung cancer was also increased among subjects in the upper half of the highest tertile of life-time pendimethalin exposure days (RR = 5.2, 95% CI = 1.6–17.3, Ptrend = 0.03), compared with low-pendimethalin-exposed applicators. The association was more pronounced for adenocarcinoma of both rectum and lung. Conclusion Our findings suggest a possible association between pendimethalin exposure and incidence of rectum and lung cancers among pesticide applicators in the U.S.-based Agricultural Health Study