AbstractThe dissipation of the insecticide deltamethrin was studied in natural prairie ponds (0 3–1 3 ha, 1–1 5 m depth) following aerial application Four ponds were treated at normal field rates (7 5 g/ha) with deltamethrin, two in June 1986 and two others in June 198−Parts per billion concentrations of deltamethrin were observed in the surface microlaver (0 12 mm, sampled with a glass plate) in all treatments during the first 8 to 12 h after application Levels of deltamethrin were about 1000‐fold lower in subsurface water (10–20 cm depth) Pseudo first order half‐lives of deltamethrin in the surface film varied from 0 6 to 5 h and were influenced by macrophvte density and amount of sprav deposit Half‐lives of deltamethrin in subsurface waters were less variable, averaging 14 h Deltamethrin was not detected in sediments (0–2 5 cm depth containers, detection limit 10 ng/g dry weight) following sprav application in either year The stereoisomer (αR, 1R/α S 1S‐cis‐) was detected in subsurface water along with a cyclopropvl acid derivative (DBCA) and phenoxybenzoic acid (PBA) Concentrations of DBCA and PBA 10 to 100 fold higher than that of the parent compound persisted in subsurface water for 18 to 25 d after spray deposition The surface film influenced the overall fate of deltamethrin by reducing diffusive transport to subsurface waters and increasing the amount of the insecticide available for volatili
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