Use of outdoor freshwater pond microcosms: I. Microcosm design and fate ofpyridaben

An outdoor freshwater microcosm study was conducted in which pyridaben, an insecticide-miticide, was directly applied to water to determine its fate a nd biological effects on an aquatic community. The following paper describe s the design, specific techniques, and fate of pyridaben in microcosms incl uding model prediction of the estimated environmental concentration, wherea s the subsequent paper describes the responses of biota. An analysis of Var iance design was used with four treatments in which pyridaben was applied a s an aqueous suspension (75% wettable powder) at three concentrations (0.34 , 3.4, 34.0 mu g/L) plus an untreated control to 24 microcosm tanks (23 m(3 )). Each treatment was replicated six times. Pyridaben was applied to each microcosm once in April and once in May 1993 to simulate actual crop applic ation. The Exposure Analysis Modeling System predicted that as a result of a drift (5.0%) exposure scenario, the half-life of pyridaben in water was 3 0 to 34 h. The model also predicted negligible concentrations of pyridaben in sediment after drift. Surface runoff was not considered an important sou rce of pyridaben to aquatic systems, because the Pesticide Root Zone Model predicted a maximum runoff concentration of 0.1 mu g/L. The half-life in mi crocosm water for the low, middle, and high treatment concentrations for bo th applications ranged from 11.8 to 28.5 h. After both applications at 3.4 mu g/L, pyridaben was not detected in sediment within 24 h, whereas at 34.0 mu g/L the half-life of pyridaben in sediment was 9.8 d.