Comparison of pesticide deposition sampling methods for spray drift of atrazine

Abstract

Off-target deposition is a potential route of pesticide entry into the environment. To determine off-target deposition of pesticides, various deposition samplers are used. A study was carried out to compare a number of deposition samplers (chromatography paper, glass microscope slides, glass petri dishes, polyacrylic rods) used in spray drift determination of atrazine (and terbuthylazine when present in the formulation). The first sampling campaign was conducted to compare three horizontally oriented deposition samplers (glass microscope slides, chromatography paper, and glass petri dishes) and two vertically oriented deposition samplers. The second sampling campaign consisted of horizontal and vertical chromatography paper only, as this sampler provided the best results in the first sampling campaign. In each of the spraying events of atrazine three sampling lines were used. In the first application, the sampling distances were 0, 10, 25, 50, 100, 200, and 400 m. In the second application, the sampling distances were 0, 10, 30, 50, and 100 m. In addition, corresponding upwind control deposition samplers were also included in each pesticide sampling campaign. Analysis of pesticide deposition samples for both sampling campaigns was done by GC-MSD. The limit of detection (LOD) for atrazine was 0.006 μg.ml-1 (1st sampling campaign) and 0.01 μg.ml-1 (2nd sampling campaign), and 0.02 μg.ml-1, for terbuthylazine (2nd sampling campaign) respectively. Excellent recoveries of >70% were obtained by sonication extraction of chromatography paper, glass petri dishes, glass microscope slides, and polyacrylic rods. The precision in terms of %RSD was less than 20%. In the first sampling campaign, the chromatography paper was the best deposition sampler, and atrazine levels deposited on the samplers were up to 0.012 μg.cm-2. In the second sampling campaign, both atrazine and terbuthylazine were detected, and deposition levels were up to 11 μg.cm-2, and 12 μg.cm-2 respectively. Comparison of field deposition data and AgDISP modelled data showed that the model under-predicted the amount of atrazine in the first sampling campaign. In the second sampling campaign, the model under-predicted only at 0 m, but as the distance increased, there was agreement between the AgDISP and the field deposition results. Thus, the findings of this study make it apparent that field deposition studies are still important to arrive at buffer distances that accurately reflect environmental concentrations of off-target deposition during pesticide application. For the first time, this project has shown the comparison of various samplers with different materials of construction in the off-target deposition of a pesticide active ingredient (atrazine), under local South African conditions.