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Primary and secondary pesticide drift under sub-humid climate; field measurements and modeling approaches

Ohad Zivan, Ph.D.

Background: Extensive use of pesticide is an essential part of modern agriculture. However, there is growing concern regarding off-target contamination due to pesticide drift from treated fields, and exposure of adjacent rural communities. Pesticide drift includes both spray drift during application (Primary drift) and post-application drift (Secondary drift) mainly resulting from evaporation of the applied pesticide. Quantitative knowledge on pesticide drift is still lacking. Most research has focused on primary drift and deposition of airborne pesticide, while much less attention has been given to atmospheric transport of smaller aerosols and gaseous pesticides. The case is more severe for secondary drift, especially for hot and semi-arid climate.

Aims: To assess, in semi-arid climate, primary and secondary drift of pesticide to rural communities adjacent to agricultural fields.

Methods: Concentrations of airborne Chlorpyrifos and Dichlorvos (organophosphate pesticides) were measured during and after application in a community adjacent to a treated field (~70m from field edge) using high volume samplers equipped with quartz filters and polyurethane foam plugs for aerosols and gases sampling, respectively. In addition, pesticide drift during applications were simulated using non-steady state CALPUFF atmospheric modeling software.

Results: Despite the distance from treated field, in all application events elevated atmospheric pesticide concentrations were observed during application (few µg*m-3) and in the following days (tens to hundreds ng*m-3). Modeling results predicted well the temporal trend but underestimated observed concentrations.

Conclusions: Rural communities adjacent to treated fields are exposed to primary and secondary pesticide drift, resulting in inhalation exposure that may not be negligible. CALPUFF provides a useful tool to model pesticide primary and secondary drift, but emissions estimations from treated fields still need to be improved.

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