Occupational Exposure to Metribuzin and the Incidence of Cancer in the Agricultural Health Study
Received 12 August 2008; accepted 23 December 2008. published online 16 April 2009.
Purpose
Little is known about the potential carcinogenicity of the triazinone herbicide metribuzin. We evaluated the association between metribuzin use and cancer risk in the Agricultural Health Study, a prospective cohort study of licensed pesticide applicators in Iowa and North Carolina.
Methods
Applicators (N=23,072) provided information on metribuzin use on a self-administered questionnaire at enrollment (1993–1997). Among metribuzin users (n=8,504), there were 554 incident cancer cases. We used multivariable Poisson regression to evaluate potential associations between metribuzin use and cancer incidence by using two quantitative exposure metrics, lifetime days and intensity-weighted lifetime days.
Results
Using intensity-weighted lifetime days, the rate ratio (RR) and 95% confidence interval (CI) for the highest exposed tertile for lymphohematopoietic malignancies were 2.09 (95% CI: 0.99–4.29), p trend=0.02 and 2.42 (95% CI: 0.82–7.19), p trend=0.08 for leukemia. For non-Hodgkin lymphoma, the RR was 2.64 (95% CI: 0.76–9.11), p trend=0.13 for lifetime days and 2.52 (95% CI: 0.66–9.59), p trend=0.13 for intensity-weighted lifetime days. Patterns of association were similar for both exposure metrics, but associations were generally weaker than for intensity-weighted days.
Conclusions
The results from this study suggest a potential association between metribuzin use and certain lymphohematopoietic malignancies; however, having not been observed previously, caution should be used in interpretation.
aEmory University Rollins School of Public Health, Department of Epidemiology
bAmerican Cancer Society, Department of Epidemiology and Surveillance Research
cDivision of Cancer Epidemiology and Genetics, National Cancer Institute
dEpidemiology Branch, National Institute of Environmental Health Sciences
Address correspondence to: Dr. Laura E. Beane Freeman, National Cancer Institute, Division of Cancer Epidemiology and Genetics, 6120 Executive Blvd., Room 8112, Bethesda, MD 20892-7240. Tel: (301) 451-8793. fax: (301) 402-1819.
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