Because of growing concerns over the potential risks from exposure to airborne pesticides that have acute and chronic human and ecological health impacts, information on concentrations in air downwind of emission sources is being increasingly required, especially in populated areas. A simple and cost-effective approach to estimating downwind air concentrations from emissions was developed by relating physicochemical properties of various pesticides and other organics with their published volatilization rates (flux) from treated soil, plant foliage, and water. The resulting set of ln-ln correlations was used to estimate flux for pesticides with known physicochemical properties. These estimated flux values were used as source strengths in the EPA's SCREEN-2 dispersion model to calculate downwind concentrations near treated fields for time periods soon after application. Using estimated flux values for carbofuran, oxydemeton-methyl, methidathion, azinphos-methyl, and molinate, downwind concentrations were calculated that compared well with concentrations measured near treated fields for these pesticides applied to field crops, orchards, and rice fields. This approach is useful for prioritizing pesticides that pose potential health hazards and for which monitoring should be considered.
Methyl bromide (MeBr) is used extensively in agriculture as a soil fumigant and there is growing concern over the role it may play in the depletion of stratospheric ozone. Methyl bromide is applied using various techniques and very little is known about how much of the applied fumigant volatilizes into the atmosphere after the application. This field study was designed to estimate the post‐application methyl bromide volatilization loss rates from two different application practices. The fields were approximately 6 km apart in Monterey County, California, and were treated in conformity with local practices as of 1992. The MeBr was injected at a depth of 25 to 30 cm. One field was covered simultaneously with a high‐barrier plastic film tarp during the application, and the other was left uncovered, but the furrows made by the injection shanks were bedded over. Volatilization fluxes were estimated using an aerodynamic‐gradient technique immediately following the completion of the application process and continued for 9 d for the tarped field and 6 d for the nontarped field. The cumulative volatilization losses from the tarped field were 22% of the nominal application within the first 5 d of the experiment and about 32% of the nominal application within 9 d including the one day after the tarp was removed on Day 8 after application. In contrast, the nontarped field lost 89% of the nominal application by volatilization in 5 d. The volatilization rate from the tarped field was shown to be significantly lower than the nontarped field at a 95% confidence level.
Pesticide emissions to air have been shown to correlate with compound vapor pressure values taken from the published literature. In the present study, emissions correlations based on vapor pressures derived from chemical property estimation methods are formulated and compared with correlations based on the literature data. Comparison was made by using the two types of correlations to estimate emission rates for five herbicides, a fungicide, and an insecticide, for which field-measured emission rates from treated soil, foliage, and water were available. In addition, downwind concentrations were estimated for two herbicides, three fungicides, four insecticides, and two fumigants, for which concentration measurements had been made near treated sources. The comparison results demonstrated that correlations based on vapor pressures derived from chemical property estimation methods were essentially equivalent to correlations based on literature data. The estimation approach for vapor pressures is a viable alternative to the inherently more subjective process of selecting literature values.
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