Project at a Glance

Title: Pesticides in air. Part II: Development of predictive methods for estimating pesticide flux to air.

Principal Investigator / Author(s): Hsieh, Dennis P H

Contractor: UC Davis

Contract Number: 92-313

Research Program Area: Emissions Monitoring & Control

Topic Areas: Agriculture, Modeling, Stationary Sources, Toxic Air Contaminants


This project consisted of two parts: (1) A literature review of post-application pesticide volatilization flux values that have been measured or modeled and (2) development of predictive tools for estimating post-application flux derived from correlations of pesticide physicochemical properties and measured flux reported in the literature (residue drift during application was not considered in this project). Part (2) was the primary goal of the project since a method for predicting pesticide flux would enable Air Resources Board personnel to predict the levels at which pesticides are likely to be found in the ambient air. This information would allow the prioritization of pesticides that pose potential health problems and for which monitoring should be considered. A review of the literature reporting on pesticide volatilization flux from soil, water, crop surfaces, generated using lab chambers, field measurements, or various modeling and other approaches, is divided into four main sub-headings: Category I -- field / laboratory flux chambers; category II -- meteorological methods; category III -- indirect residue analysis; and category IV -- mathematical modeling. Of the field/laboratory studies of pesticide volatilization flux, about 53 percent dealt with residues on soil, while 32 percent dealt with residues on foliage and the remaining 15 percent with residues in water. The references fall primarily in categories I, II, and IV (37percent, 27 percent and 26 percent, respectively), with category III constituting only 10 percent of the references. Our own efforts toward developing predictive flux tools took information from categories I-III for pesticides applied to soil, incorporated into soil, applied to crop surfaces and applied to water and correlated the physicochemical properties of those pesticides with their published evaporative flux values, resulting in a set of mathematical correlations. These correlations were derived from the following pesticide physicochemical properties: (1) Soil adsorption [KOC], water solubility [SW], and vapor pressure [VP] for residues on soil; (2) KOC, SW, VP, application rate [AR], and depth of incorporation [d] for residues incorporated into soil; (3) VP only for residues on crop surfaces; and (4) VP and SW for residues dissolved in water (in this case, evaporative flux was normalized to water concentration). In all cases, chemical properties and evaporative flux correlated well. These correlations could be used to estimate flux for chemicals that have known physicochemical properties. Using these estimated flux values as source strengths in the EPA's SCREEN-2 model, we calculated downwind concentrations for carbofuran, oxydemeton-methyl, methidathion, azinphosmethyl, and molinate that compared well with CARB-measured concentrations for these pesticides applied to field crops, orchards, and a rice field.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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