Correlation Techniques for Estimating Pesticide Volatilization Flux and Downwind Concentrations

Abstract

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.

Fate in the Environment and Long-Range Atmospheric Transport of the Organophosphorus Insecticide, Chlorpyrifos and Its Oxon

“…The average initial flux was approximately 1,500 μg CPY m −2 h −1 and decreased by a factor of approximately 200-7.2 μg CPY m −2 h −1 . In an earlier study, the eddy correlation micro-meteorological technique was used to estimate evaporation fluxes for several pesticides including CPY in the days following application in California (Woodrow and Seiber 1997). For CPY, a flux of 92.3 μg m −2 h −1 was calculated following application of 1.5 kg CPY ha −1 , which is equivalent to 0.15 g CPY m −2 .…”

“…During these periods on the surface and in the atmosphere, there is direct photolysis of CPY to CPYO. A detailed characterization of the initial 12 h period is given by Rotondaro and Havens (2012), while studies by Woodrow et al (Woodrow and Seiber 1997;Woodrow et al 2001) characterized average volatilization during the day or 2 following application. In the context of modeling volatilization losses, the simplest approach is to determine the total applied quantity and area treated, assume an immediate volatilization loss of 10-20% followed by a period of slower volatilization at an approximate initial rate of 1% per day decreasing with a half-life of approximately 3 d to 0.1% after 10 d. Rain and temperature will affect these rates.…”

“…In the context of modeling volatilization losses, the simplest approach is to determine the total applied quantity and area treated, assume an immediate volatilization loss of 10-20% followed by a period of slower volatilization at an approximate initial rate of 1% per day decreasing with a half-life of approximately 3 d to 0.1% after 10 d. Rain and temperature will affect these rates. For illustrative modeling purposes, it was assumed that a typical rate of application is 1.5 kg CPY ha −1 , which corresponds to 0.15 g CPY m −2 (Woodrow and Seiber 1997) to an illustrative area of 1.0 ha (10 4 m 2 ).…”

“…Such estimates are nonetheless useful to estimate the order of magnitude of these "source" concentrations when monitoring data have been obtained in the vicinity of sources. The SCREEN3 model has been used to estimate concentrations in air at ground-level (1.5 m) immediately downwind, such as 10-30 m, from treated crops (Woodrow and Seiber 1997). Measured concentrations of five pesticides were of similar magnitude to predicted concentrations (μg m −3 ) and similar in magnitude to estimated fluxes (μg m −2 s −1 ), a result that is consistent with the ratio of these two parameters being approximately 1 m s −1 .…”

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

“…Past studies of off-target pesticide drift have characterized the movement of the pesticide spray using tracer dyes, deposition and air sampling, foliar residues, and modeling techniques (Draper et al, 1981;Barnes et al, 1987;Gilbert and Bell, 1988;Riley et al, 1989;Clark et al, 1991;Salyani and Cromwell, 1992;Woodrow et al, 1997;Garcia et al, 2000;Richards et al, 2001;Woods et al, 2001). No studies to date have incorporated environmental sampling and biomarkers of exposures before, during, and following applications when assessing children's potential for exposure to pesticide drift.…”