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Last Edited: 10/18/2007

Pesticide Use in California: US/Mexico Border Region, Final Report
Written: 2000

Analytical Procedures, Methodologies, and Field Protocols to Monitor and Determine Environmental Contaminants

To assist the U.S. Environmental Protection Agency (EPA) in determining where potential pesticide exposures are occurring in children near the U.S./Mexico border, pesticide use report (PUR) data from the California Department of Pesticide Regulation (CDPR) was analyzed for the years 1991-1995 for two California border counties, San Diego and Imperial. In California, all agricultural pesticide use (pounds of product applied) is reported by growers to local and state pesticide regulatory agencies. The site of application is identified to an area of approximately one square mile. The CDPR converts pounds of pesticide product applied to pounds of active ingredient.

The quality of the pesticide use data was assessed, including evaluation of the completeness of the data and potential errors (outliers). Toxicological evaluation of the top ten pesticides by weight for each year and county was undertaken. Pesticides were classified as respiratory irritants, possible/probable human carcinogens, reproductive/developmental toxicants, and acethylcholinesterase inhibitors. Relevant animal and human literature, along with classifications by other agencies, were reviewed to classify pesticides. The top pesticides by frequency of application, and the top crops applied with pesticides were examined. Time and seasonal trends of pesticide use was analyzed by year. Locations of sites where children are likely to congregate in the two counties, including schools, day care centers, churches, migrant camps, and parks were linked to a geographic information system (GIS) for analysis. Data from the 1990 U.S. Census and updated population estimates, along with digital coverages of residential land use, were also imported into the GIS to identify population areas. Schools and census tracts were ranked by proximity to total annual volume of pesticide applications and by total annual volume of respiratory irritants.

Data quality assessment of the pesticide use data revealed that the data appear to be reasonably accurate, as the majority of the data fell in manufacturer’s ranges for application rates, and the geographic distribution of pesticide use closely coincides with agricultural land use. Evaluation of the frequency of data entry and grower errors was severely limited due to the restricted availability of hard copy forms. Although outliers in application rates were found to comprise 0.1% or less of the total applications, adjustment of these large applications resulted in changes of the ranking of the top ten pesticides.

Pesticide use (number of pounds applied) in Imperial County was found to be 4-8.5 times higher than in San Diego County over the time period examined. From 1991-1995, total pesticide use increased 24% in Imperial County (from 6.5 to 8.1 million pounds), and 7% in San Diego County (from 888 to 947 thousand pounds). The top 10 pesticides by weight (in 1995) in Imperial County were metam-sodium, sulfur, methyl bromide, malathion, trifluralin, methomyl, EPTC, chlorthal-dimethyl, chlorpyrifos, and dimethoate. In San Diego County, the top 10 pesticides by weight (1995) were methyl bromide, petroleum oil, chloropicrin, mineral oil, metam-sodium, glyphosate, sulfur, potash soap, chlorothalonil, and copper hydroxide.

Geographic analysis of pesticide use and population centers showed that although the total population and population density of children is lower, heavy use of pesticides such as respiratory irritants are more likely to be applied near residential areas in Imperial County than in San Diego County. Sixty-nine percent of Imperial County census tracts had agricultural pesticide applications within their boundaries, compared to only 19% of the census tracts in San Diego County. Pesticide use near schools (within 2.8 miles) in Imperial County was approximately 10 times higher than in San Diego County (33,040 vs. 3355 pounds per public school; and 23,898 vs. 2725 pounds per private school). In Imperial County, all schools with children aged 11 years and younger had agricultural use pesticides applied within 2.8 miles of the school. In San Diego County, 55% of schools with children aged 11 and younger had pesticide applications within 2.8 miles of the school.

This analysis was limited by the lack of currentness of some of the locations of sites where children reside. Actual locations within the one square mile area where pesticides are being applied are not known. Although children may be residing or attending schools near pesticides applications, the PUR data only allowed the mapping of agricultural pesticide use, but not exposure. California has stringent regulations of the use of pesticides aimed at protecting the public. In order to determine the extent of any exposure, environmental monitoring would be required. The U.S. EPA is currently planning on conducting such monitoring in selected locations of the border area. This study may assist the EPA as a sampling frame for selecting monitoring locations.

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