Ph.D Thesis

Ph.D StudentZivan Ohad
SubjectA Study of Primary and Secondary Pesticide Drift
from an Orchard
DepartmentDepartment of Civil and Environmental Engineering
Supervisors ASSOCIATE PROF. Yael Dubowski
Full Thesis textFull thesis text - English Version


Pesticides are considered an essential part of modern agriculture. However, over the past few decades, there are increasing concerns regarding pesticide drift and the resulting exposure of nearby communities to harmful drifted chemicals. Unfortunately, although atmospheric transport of pesticides is considered as a major loss path of pesticide from target area, there is still a large gap of knowledge regarding its spreading and health consequence.

Pesticide drift can be divided into Primary (during application) and Secondary drift (after application ceased). Previous studies have shown that pesticide drift is a complex phenomenon affected by multiple parameters.  Furthermore, the complex micrometeorology above orchard canopy imply that to estimate pesticide flux from it, air measurements should be done up to a sufficient height above the surface. However, currently available drift measurements from orchards were done only below canopy height.

The main objective of this work was to improve our understanding of primary and secondary drift from orchard applications, under Mediterranean climate.  The work included three major parts: (1) pesticides’ air measurements at the minimal buffer distances defined by current Israeli regulations (50 & 100 m for ground applications; 120 m for aerial applications), (2) investigation of pesticide drift profile at close proximity to orchard under various conditions, and (3) adaptation of simple air pollution dispersion model to describe near and far field drift dispersion.

 Pesticide drift was monitored following 21 ground applications and five aerial applications. All ground applications were done in the same peach orchard, while sampling at varying distances and heights. In addition to pesticide measurements, meteorological parameters were also monitored.

During ground applications pesticides were detected at all sampling distances (i.e., 7, 20, 50 and 100m away from the orchard), at concentration range of hundreds to a few . Furthermore, at 7 and 20m distance pesticide reached the highest sampling height of 10m, which is more than thrice the canopy height. Interestingly, there was almost no decline in concentrations with height.

Secondary drift was measured at several intervals to understand its temporal trend. For all tested pesticides, there was a reduction at air concentrations with time, however trends varied between pesticides of different vapor pressure. The overall pesticide load drifted from the orchard during secondary drift was not negligible compare to the primary drift (excluding the nonvolatile pesticide). Surprisingly, secondary drift also reached height of 10m (measured at 7 and 20m distance). To the best of our knowledge, this is the first work to measure secondary drift up to thrice the canopy height.

Considering it is not possible or feasible to measure everywhere, computer models are used. Here, two simplified models were inspected for their potential to predict pesticide drift. A modified Gaussian puff model to better represent the primary drift at very close proximity to the source. For medium and far distances from source location a commercial model (CALPUFF) that can calculate a more complex wind field was examined. Both models showed similar trends to those observed during field measurements.