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Last Edited: 10/18/2007

Soil sampling at schools in Imperial County, California
Written: 2000


The Environmental Health Investigations Branch of the California Department of Health Services, as part of ongoing research on the United States/Mexico Border, previously identified schools in Imperial County with nearby agricultural use of pesticides. The Environmental Health Investigations Branch received further funding from the United States Environmental Protection Agency to conduct a pilot study of pesticide concentrations in soil at schools in Imperial County. The goal was to assess whether the collection and analysis of soil from schoolyards was a feasible method to study the relationship between agricultural pesticide use and potential exposures to children.

A laboratory method was identified that could potentially measure 20 pesticides used agriculturally near schools in Imperial County as well as the now banned pesticide, DDT and its environmental breakdown products, DDD and DDE. The two schools with the highest nearby agricultural usage of pesticides near schools in Imperial County were selected. In July 1999, eight soil samples were collected at these schools at 100 feet from the school fenceline nearest to agricultural fields. A comparison school with much less nearby agricultural usage of pesticides was selected. At this comparison school four soil samples were collected at the fenceline.

Field and laboratory quality control parameters were not acceptable for ten target analytes (chlorathaonil, dimethoate, disulfoton, DDT, endosulfan I, endosulfan II idrodione, metalaxyl, cis-premethrin and sethoxydim). These nine are not considered appropriate for futher study by the laboratory methods utilized.

Field and laboratory quality control parameters were acceptable for 13 pesticides. Of these, eight were not detected in any sample. The eight were atrazine, carbofuran, chlorpyrifos, cycloate, fonofos, linuron, malathion, and trans-permethrin. This absence of detections is consistent with the estimated short environmental fate of most of these compounds. These eight pesticides are not considered appropriate for further study of soil at schools in Imperial Valley.

Five compounds (DDD, DDE, chlorthal-dimethyl, diazinon, and trifluralin) were reliably measured and detected at low part per billion (ppb) levels in soil. The levels detected are low and considered safe for children to contact. The detection of trifluralin--the compound with the highest agricultural use and the compound with the longest estimated environmental half-lives of all pesticides agriculturally applied near the schools--suggests that any additional sampling should be done in conjunction with environmental fate information. Future exposure or soil studies may be warranted at "sensitive" receptors, such as schools. Such studies would assist in defining whether there is a relationship between agricultural use and potential pesticide exposure to children.

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