M.Sc Thesis

M.Sc StudentKatzman Doron
SubjectAssessing the Impact of a Polymeric Spray Drift Retardant
Adjuvant on the Reduction of Airborne Pesticides
DepartmentDepartment of Civil and Environmental Engineering
Supervisor ASSOCIATE PROF. Yael Dubowski


Pesticide are used worldwide for pest control in various scenarios; large quantities of these hazardous chemicals are applied to agricultural lands in order to keep pests at bay and achieve high crop yields, much needed to support the growing world population. When pesticides are applied to a field as spray, significant portions may be lost due to atmospheric transport during application (Primary drift) and at the period following it (Secondary drift).

Such airborne pesticide can sediment in the vicinity of the emission area or remain airborne and travel over large distances in the atmosphere, posing risk to various sensitive targets in its path. Sensitive targets of such may include human-beings, crops, or any sensitive ecological system. Therefore, minimizing pesticide drift is highly desired and much efforts have been put to achieve reduction by different means.

Chemical adjuvants, added to the sprayer's tank mix, are used in order to alter the spray solution's physicochemical properties and produce larger droplets. Many studies concluded that shifting the droplet size distribution toward larger droplets is followed by a reduction in drift, and so, such "drift reducing adjuvants" have become commonly used. However, most studies addressing drift reduction, as well as regulatory efforts to protect sensitive targets (e.g., defining buffer zones, where strips of land are left unsprayed), rely on measurements of sedimenting droplets. Such approach does not address pesticides present in small aerosols or vapor phase, which are highly susceptible to drift and may pose human health risk by penetrating into the respiratory system.

In this work, the effect of a polymer-based adjuvant on the drift of airborne pesticides was examined during two field studies using active air sampling. The results of these studies suggest higher primary drift of airborne pesticides when the adjuvant was used. This conclusion was supported by comparing the field measurements to drift results obtained by a modified Gaussian puff dispersion model, which enabled to compensate for variations in meteorological conditions during the field experiments. In order to explain such findings, the effect of the adjuvant on droplet size distribution produced by common nozzles was examined in a wind tunnel. It was shown that although the desired shift of volumetric distribution toward larger droplets was achieved, the adjuvant also led to a significant increase in the number of fine droplets. 

Regarding secondary drift, the field measurements suggested that the adjuvant only had a minor impact on it, which can also be explained by temperature and relative humidity variations. Nevertheless, complimentary laboratory experiments suggested that the adjuvant resulted in an enhancement in pesticide volatilization and photolysis rates, which could be attributed to the larger area of films produced in its presence or to its effect on film surface morphology and pesticide distribution within it.