Agrochemicals undergo transport away from treatment areas by a number of mechanisms, including drift, volatilization, runoff, leaching, etc. This may account for significant losses of pesticides to the environment (Woodrow, Seiber, and Gibson, 2019). Transport and deposition of pesticides in fog and in the environment in the vicinity of pesticide use areas , first reported in the 1980s (Glotfelty, et al (1987), involves phase transfers of spray drift vapors, aerosols and particulate matter, and deposition of pesticides entrained in the fog. This has been reported for fog-prone food production areas, such as the Salinas Valley of California (Schomberg et al, 1991 ). Turner et al(1989) reported on inadvertent fog-derived residues in row crops(1989). Pesticides with low Henry’s constants, reasonable persistence in air and water, and use in times of the year when fogs form, are most likely to be transported and deposited in fog water. The resulting deposition may be a significant but largely overlooked source of residues in food and water. Commodities without a tolerance established for the crops receiving this input may be prevented from entering the food supply. Examples of pesticide residues in fogwater include organophosphates (diazinon, parathion, chlorpyrifos, methidathion) and some breakdown products such as paraoxon and chlorpyrifos oxon. Some compounds showed enrichment in the fog water beyond that expected based only on Henry’s law constant considerations. But the contribution of fog borne residues to exposures of humans was not considered to pose a significant health risk under most conditions. For wildlife, the residue exposure can be more significant, since fur and /or feathers can aid in the capture and retention of airborne residues. For redtailed hawks in almond orchards (Wilson et al, 1981) this exposure pathway needs to be taken into account, particularly for oxons of some OPs. This presentation will summarize results to date, and steps which can be taken to minimize exposure to pesticides in fog.

Transport and deposition of pesticide residues in fog

2019 Fall National Meeting

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