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Spray Deposition of Two Insecticides into Surface Waters in a South African Orchard Area

^a Dep. of Zoology, Private Bag X1, Univ. of Stellenbosch, Matieland 7602, South Africa
^b Forensic Chemistry Lab., Dep. of Health, Cape Town 8000, South Africa

View larger version (49K): [in a new window]   Fig. 1. Location of sampling sites (left): LR, sampling site in the Lourens River; END, site for the endosulfan trials; AZI, site for the azinphos-methyl trials. Plot schematic (right) depicting the orientation of spray deposit collectors and sampling sites for tributary water samples during the azinphos-methyl trials with a 10-m distance between tree row and tributary.

View larger version (31K): [in a new window]   Fig. 2. Spray deposition (±SE) of azinphos-methyl at different distances downwind of the orchard tree row (bearing pears). Squared regression coefficient for an exponential regression is R2 = 0.99.

View larger version (18K): [in a new window]   Fig. 3. Spray deposition rates of azinphos-methyl measured in the present study and 95th-percentile values for basic drift deposition according either to the German exposure assessment procedure (Federal Biological Research Centre for Agriculture and Forestry; BBA) (Ganzelmeier et al., 1995) using late growth stage or to the U.S. Spray Drift Task Force (SDTF) data set (USEPA, 1999) using high drift potential orchards.

View larger version (45K): [in a new window]   Fig. 5. Concentrations (±SE) of endosulfan in tributary water 15 m downwind of the sprayed plot. A, calculated peak concentrations based on 95th-percentile values for basic drift deposition (Ganzelmeier et al., 1995); B1, calculated peak value based on measured deposition rate; B2, measured peak value; C, measured 1-h average value.

View larger version (44K): [in a new window]   Fig. 4. Concentrations (±SE) of azinphos-methyl in tributary water 10 m downwind of the sprayed plot. A, calculated peak concentrations based on 95th-percentile values for basic drift deposition (Ganzelmeier et al., 1995); B1, calculated peak value based on measured deposition rate; B2, measured peak value; C, measured 1-h average value.