Agricultural Pesticide Use in California: Pesticide Prioritization, Use Densities, and Population Distributions for a Childhood Cancer Study. (Children's Health Articles)
Gunier, Robert B., Harnly, Martha E., Reynolds, Peggy, Hertz, Andrew, Von Behren, Julie, Environmental Health Perspectives
Several studies have suggested an association between childhood cancer and pesticide exposure. California leads the nation in agricultural pesticide use. A mandatory reporting system for all agricultural pesticide use in the state provides information on the active ingredient, amount used, and location. We calculated pesticide use density to quantify agricultural pesticide use in California block groups for a childhood cancer study. Pesticides with similar toxicologic properties (probable carcinogens, possible carcinogens, genotoxic compounds, and developmental or reproductive toxicants) were grouped together for this analysis. To prioritize pesticides, we weighted pesticide use by the carcinogenic and exposure potential of each compound. The top-ranking individual pesticides were propargite, methyl bromide, and trifluralin. We used a geographic information system to calculate pesticide use density in pounds per square mile of total land area for all United States census-block groups in the state. Most block groups (77%) averaged less than 1 pound per square mile of use for 1991-1994 for pesticides classified as probable human carcinogens. However, at the high end of use density (> 90th percentile), there were 493 block groups with more than 569 pounds per square mile. Approximately 170,000 children under 15 years of age were living in these block groups in 1990. The distribution of agricultural pesticide use and number of potentially exposed children suggests that pesticide use density would be of value for a study of childhood cancer. Key words: agriculture, childhood cancer, ecologic study, epidemiologic study, exposure assessment, geographic information systems, pesticides, risk assessment. Environ Health Perspect 109:1071-1078 (2001). [Online 2 October 2001] http://ehpnet1.niehs.nih.gov/docs/2001/109p1071-1078gunier/abstract.html
Some epidemiologic studies suggest an association between pesticide exposure and childhood cancer (1,2). Most studies have used questionnaires to evaluate parental occupational exposure around the time of the child's birth and exposure to the parents or child from pesticide use in the home and garden. Such information is potentially limited by response bias. Childhood cancer has not been evaluated with respect to potential exposure to agricultural pesticides because respondents are unlikely to have specific knowledge about pesticide use on nearby fields.
Few tools exist for identifying regions with a high density of agricultural pesticide use. County crop acreage totals are available, but land use varies tremendously within California counties because of differences in topography and urbanization. Some investigators have used satellite imagery and a geographic information system (GIS) to identify the location of agricultural fields (3,4). These indices provide information on the population living near fields, but only indirect estimates of pesticide use based on crop type. The resulting pesticide use estimates are limited by crop misclassification and the assumption that all fields are treated similarly for a given crop. Some studies of cancer in adults have been conducted with pesticide use data summarized at the county level (5-7). However, the number of residents living near agricultural fields and the amount of specific pesticides applied agriculturally in these communities have generally not been available.
In 1992, California accounted for 22% of all agricultural pesticide use in the United States (8). There has been some form of pesticide use reporting in California for several decades, although before 1990 reporting was limited to applications that were restricted and required a permit. The California legislature mandated the Pesticide Use Report (PUR) system in 1990 (9), legally requiring growers and applicators to report all commercial agricultural pesticide use. Every month, written or electronic records of all pesticide applications are submitted to the county agricultural commissioners. …