Does polyacrylamide-based adjuvant actually reduce primary drift of airborne pesticides?

Atmospheric drift of pesticides sprayed outside treated fields may pose serious environmental and health concerns. Chemical adjuvants, among other techniques, reduce drift by modifying the physicochemical properties of the pesticide solution, which presumably produces larger droplets upon spraying that are less prone to drift. Previous studies, that have addressed the effect of adjuvants on drift reduction, mainly rely on measurements of droplet sedimentation while ignoring the presence of pesticides in the forms of small aerosols and vapor. Such forms are expected to be highly susceptible to atmospheric drift that may pose human health risk via inhalation exposure. The present study examines the effect of a polymer-based adjuvant on airborne-pesticide drift using active air sampling in two field campaigns. Surprisingly, these measurements indicate higher primary drift (PD) of airborne pesticides in the presence of adjuvant in the spraying solution. The results are further supported by comparing measured drifts to those calculated using a modified Gaussian puff dispersion model, which enabled to evaluate the impact of varying meteorological conditions during the field experiments. In addition, the adjuvant effect on droplet size distribution generated by common nozzles, was tested in a wind tunnel. The resulting size-distributions demonstrated that while the addition of adjuvant resulted in a desired shift of the volumetric distribution towards larger droplets, it also led to a significant increase in the number concentration of fine droplets. Such trends can explain how the addition of polymeric adjuvant can yield both, a reduction in sedimenting drift outside treated areas and an increase in airborne PD intensity, as observed in the present study. This study demonstrates the complex effect of chemical adjuvants and the urgent need to further explore and understand their environmental impact.