Childhood Leukemia and Residential Proximity to Agricultural Pesticide Applications

Abstract

MAA2-PD-09 Introduction: A number of studies suggest that household pesticide use may be a risk factor for childhood leukemia, but few have evaluated risk relationships for nearby agricultural pesticide use. The U.S. Environmental Protection Agency lists several pesticides used on agricultural crops as probable (class B2) or possible (class C) carcinogens. Ambient exposures to these compounds are a major source of public concern. Methods: Risk relationships were estimated for nearby agricultural pesticide applications associated with the lifetime residential histories for 158 cases and 243 controls enrolled in the Northern California Childhood Leukemia Study (NCCLS). Cases were diagnosed between 1999 and 2002 in the 35-county study area, including the highly agricultural Central Valley. Controls were selected from California birth files and individually matched to cases based on date of birth, sex, and race/ethnicity. Cumulative lifetime proximity to agricultural applications of specific pesticides within one half mile of subjects’ residences was ascertained by linking subjects’ residential histories with data from the California Pesticide Use Reporting system. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using conditional logistic regression. Results: Cumulative lifetime residential proximity was observed in 47% of cases and 37% of controls for pesticides classified asprobable (class B2) carcinogens, and in 53% of cases and 46% of controls for possible (class C) carcinogens. In preliminary analyses, the risk of childhood leukemia increased with residential proximity to probable carcinogens (OR = 1.56; 95% CI = 1.01–2.40) or possible carcinogens (OR = 1.38; 95% CI = 0.90–2.11). We did not observe risk increases associated with lifetime residential proximity to pesticides classified as genotoxins or developmental toxins. Discussion: These preliminary findings suggest that living near agricultural applications of pesticides classified as carcinogens may increase the risk of childhood leukemia. Current and future investigations will evaluate potential exposures to specific carcinogenic pesticides and genetic susceptibility to agricultural pesticide exposures. In addition, we will assess residential proximity to agricultural pesticide use occurring during specific periods such as early life and during gestation and evaluate exposure estimates against household measurements.