Pendimethalin Exposure and Cancer Incidence Among Pesticide Applicators

Cancer epidemiologyCancer type: cancerStudy design: prospective cohortStudy size: 9089 exposed, 15285 non-exposedDescription of cohort(s) studied: Exposure(s) evaluated: pendimethelinImpact on risk: The risk for colorectal cancer was not associated with increasingpendimethalin exposure (for the highest exposed subjects, RR = 1.0; 95% CI = 0.3-3.4 when using the nonexposed as the referent group, or RR = 1.0; 0.2-4.4 when using the low-exposed as the referent group)Elevated risk of rectal cancer among subjects with the highest lifetime pendimethalin exposure-days compared with the nonexposed group (4.3; 1.5- 12.7)An increased risk for rectal cancer was found comparing subjects in the highest tertile with the non-pendimethalin exposed applicators (RR = 3.6; 95% CI = 1.2-11.3; P for trend = 0.02), whereas no clear pattern of RRs was observed when using the low-exposed group as the referent (2.9; 0.5-16.7; P for trend = 0.23).KEYWORDS CLASSIFICATION: analysis;Adult;Aniline Compounds;cancer epidemiology;Cohort Studies;epidemiology;Environmental Exposure;Female;Humans;Iowa;Male;Middle Aged;Neoplasms;North Carolina;poisoning;Prospective Studies;Questionnaires;Research;trends. BACKGROUND: Pendimethalin, a widely used herbicide, has been classified as a group C possible human carcinogen by the U.S. Environmental Protection Agency. We evaluated the incidence of cancer in relation to reported pendimethelin use among pesticide applicators in the Agricultural Health Study, a prospective cohort of licensed pesticide applicators in Iowa and North Carolina. METHODS: Information on pesticide use came from two questionnaires (enrollment and take-home). The present analysis includes 9089 pendimethalin-exposed and 15,285 nonpendimethalin-exposed pesticide applicators with complete information on pendimethalin use and covariates from a take-home questionnaire. We conducted Poisson regression analyses to evaluate the association of pendimethalin exposure with cancer incidence (mean follow-up = 7.5 years) using two exposure metrics: tertiles of lifetime days of exposure and tertiles of intensity-weighted lifetime days of exposure. RESULTS: Overall cancer incidence did not increase with increasing lifetime pendimethalin use, and there was no clear evidence of an association between pendimethalin use and risks for specific cancers. The risk for rectal cancer rose with increasing lifetime pendimethalin exposure when using nonexposed as the reference (rate ratio = 4.3; 95% confidence interval = 1.5-12.7 for the highest exposed subjects; P for trend = 0.007), but the association was attenuated when using the low exposed as the referent group (P for trend = 0.08). Similar patterns for rectal cancer were observed when using intensity-weighted exposure-days. The number of rectal cancer cases among the pendimethalin-exposed was small (n = 19). There was some evidence for an elevated risk for lung cancer, but the excess occurred only in the highest exposure category for lifetime pendimethalin exposure. The trends for lung cancer risk were inconsistent for different exposure metrics. CONCLUSIONS: We did not find a clear association of lifetime pendimethalin exposure either with overall cancer incidence or with specific cancer sites.