Proximity to Crops and Residential Exposure to Agricultural Herbicides in Iowa
Ward, Mary H., Lubin, Jay, Giglierano, James, Colt, Joanne S., Wolter, Calvin, Bekiroglu, Nural, Camann, David, Hartge, Patricia, Nuckols, John R., Environmental Health Perspectives
Rural residents can be exposed to agricultural pesticides through the proximity of their homes to crop fields. Previously, we developed a method to create historical crop maps using a geographic information system. The aim of the present study was to determine whether crop maps are useful for predicting levels of crop herbicides in carpet dust samples from residences. From homes of participants in a case-control study of non-Hodgkin lymphoma in Iowa (1998-2000), we collected vacuum cleaner dust and measured 14 herbicides with high use on corn and soybeans in Iowa. Of 112 homes, 58% of residences had crops within 500 m of their home, an intermediate distance for primary drift from aerial and ground applications. Detection rates for herbicides ranged from 0% for metribuzin and cyanazine to 95% for 2,4-dichlorophenoxyacetic acid. Six herbicides used almost exclusively in agriculture were detected in 28% of homes. Detections and concentrations were highest in homes with an active farmer. Increasing acreage of corn and soybean fields within 750 m of homes was associated with significantly elevated odds of detecting agricultural herbicides compared with homes with no crops within 750 m (adjusted odds ratio per 10 acres = 1.06; 95% confidence interval, 1.02-1.11). Herbicide concentrations also increased significantly with increasing acreage within 750 m. We evaluated the distance of crop fields from the home at < 100, 101-250, 251-500, and 501-750 m. Including the crop buffer distance parameters in the model did not significantly improve the fit compared with a model with total acres within 750 m. Our results indicate that crop maps may be a useful method for estimating levels of herbicides in homes from nearby crop fields. Key words: agriculture, exposure assessment, geographic information systems, herbicides, pesticides. Environ Health Perspect 114:893-897 (2006). doi:10.1289/ehp.8770 available via http://dx.doi.org/[Online 2 February 2006]
People living in agricultural areas may be exposed to pesticides through drift from agricultural fields in proximity to their homes. In orchard-producing areas of Washington State, pesticide levels in carpet dust and pesticide metabolites in urine of residents increased with self-reported proximity of homes to crop fields (Lu et al. 2000) and during the pesticide application season (Curl et al. 2002). Children in agricultural areas had five times the concentration of pesticides in their urine compared with children in an urban area (Lu et al. 2000). The presence of an agricultural worker in the home also increases pesticide levels through "take-home" exposures (Curl et al. 2002; Curwin et al. 2005; Lu et al. 2000).
Carpet dust can be a reservoir for pesticides and other chemicals because they are protected from degradation. Levels of pesticide in carpet dust were 10- to 200-fold higher than levels in soil around the home in residential (Lewis et al. 1994) and agricultural areas (Simcox et al. 1995). Previous studies have found residues in carpet dusts from both recently used pesticides (Colt et al. 1998; Curwin et al. 2005; Lu et al. 2000) and pesticides used many decades ago (Colt et al. 1998, 2004; Rudel et al. 2003).
We previously developed a geographic information system (GIS)-based method that used satellite imagery to create historical crop maps in the midwestern United States. Residences were mapped, and the extent of agricultural fields proximate to the homes was determined as a way of identifying homes with potential exposure to agricultural pesticides (Ward et al. 2000). Corn and soybeans are the major crops in Iowa; > 95% of corn and soybean acreage was treated with herbicides from the late 1970s through the 1990s (Iowa State University 1997). The aim of the present study was to determine whether crop maps are useful for predicting residential levels of crop herbicides as determined by their measurement in carpet dust samples from residences in a population-based case-control study of non-Hodgkin lymphoma (NHL). …