The Washington aerial spray drift study: Children's exposure to methamidophos in an agricultural community following fixed-wing aircraft applications

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Abstract
This study characterized exposures of eight children living in an agricultural community near potato fields that were treated by aerial application with the organophosphorus (OP) insecticide, methamidophos (O,S-dimethyl phosphoramidothioate). Exposure monitoring included air and deposition samples in the outdoor community environment, outdoor and indoor air samples at each residence, wipe samples of playground equipment, toys, indoor surfaces, and children's hands, and periodic urine samples. Monitoring occurred prior to, the day of, and 1 day following applications. Methamidophos deposition in the community was very low compared to deposition inside the boundaries of the treated fields. Community air concentrations increased from 0.05 μg/m3 (prespray) to 0.11 and 0.48 μg/m3 (spray day morning and afternoon, respectively), decreasing to 0.10 μg/m3 on the postspray day. Air concentrations outside residences followed a similar pattern; indoor levels did not exceed 0.03 pg/m3. Methamidophos residues were found on playground equipment following applications, but not on indoor residential surfaces. The median hand wipe levels increased from μg/sample (spray day), decreasing to 0.05 μg/sample (postspray day). Median concentrations of the primary methamidophos urinary metabolite were 61 μg/l before 1100 hours on the spray day, 170 μg/l after 1100 hours on the spray day, and 114 μg/l on the postspray day. Spray day metabolite levels were correlated with time outside on the spray day (rs=0.68), with spray day hand wipe levels (rs=0.67), and with postspray day metabolite levels (rs=0.64). Postspray day metabolites levels were also positively associated with postspray day hand wipe levels (rs=0.66). The documentation of children's exposure in this study does not necessarily mean that risks for these children were significantly altered, since nearly all children in the United States are exposed to some level of OP pesticides through dietary intake and other pathways. The association of metabolite levels with time spent outside, and the absence of methamidophos in homes indicates that children's exposures occurred primarily outdoors.

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