EVALUATION OF SAMPLERS FOR SPRAY DRIFT

Collection of airborne spray drift of malathion released from a ground -driven boom sprayer was investigated using six types of samplers: (1) horizontal alpha cellulose fallout sheets; (2) high-volume air sample rs; (3) sampling trains of rotary disk impactor and two bubblers (RDI) ; (4) rotating rod samplers; (5) vertical string samplers; and (6) pol yurethane foam plugs (PUF). Spray deposit was determined with marathio n residue collection on horizontal alpha cellulose sheets spaced at 3 m intervals in the spray swath and at 6-m intervals along a line perpe ndicular and downwind from the spray swath. Spray drift residues were collected by the samplers at four stations along a 90 m sampler line l ocated 30 m downwind and parallel to the spray swath. Gas chromatograp hic analysis was used to quantify the concentration of malathion. Resu lts indicated that fallout deposits (1) in the spray swath, (2) at 6, 12, 18, or 24 m from the spray swath edge, and (3) at 30 m downwind fr om the spray swath edge were approximately (1) 47, (2) 0.7, and (3) 0. 09% of the total spray application rate, respectively. The low in-swat h deposit was partially attributed to (1) a 1.2 m boom height-to ensur e that samplers of the evaluation were challenged with a uniform cloud of spray droplets, and (2) the use of a single swath width. No differ ences were observed in residue collections from high-volume air sample rs (P>0.4), rotating rod samplers (P>0.3), or vertical strings (P>0.7) at the four sampling stations. The collection from a high volume-PUF air sampler was 1108 ng/m(3), with 728 ng/m(3) from the filter and 380 ng/m(3) from the PUF. Malathion residues were not detected in the RDI under the selected test conditions. A low airflow rate of 1.2 L/min c ombined with the short duration of exposure to the moving spray cloud provided little opportunity for the RDI to collect a detectable level of malathion.