USE of outdoor freshwater pond microcosms: I. Microcosm design and fate of pyridaben

Abstract

AbstractAn outdoor freshwater microcosm study was conducted in which pyridaben, an insecticide‐miticide, was directly applied to water to determine its fate and biological effects on an aquatic community. The following paper describes the design, specific techniques, and fate of pyridaben in microcosms including model prediction of the estimated environmental concentration, whereas the subsequent paper describes the responses of biota. An analysis of variance design was used with four treatments in which pyridaben was applied as an aqueous suspension (75% wettable powder) at three concentrations (0.34, 3.4, 34.0 μg/L) plus an untreated control to 24 microcosm tanks (23 m3). Each treatment was replicated six times. Pyridaben was applied to each microcosm once in April and once in May 1993 to simulate actual crop application. 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 30 to 34 h. The model also predicted negligible concentrations of pyridaben in sediment after drift. Surface runoff was not considered an important source of pyridaben to aquatic systems, because the Pesticide Root Zone Model predicted a maximum runoff concentration of 0.1 μg/L. The half‐life in microcosm water for the low, middle, and high treatment concentrations for both applications ranged from 11.8 to 28.5 h. After both applications at 3.4 μg/L, pyridaben was not detected in sediment within 24 h, whereas at 34.0 μg/L the half‐life of pyridaben in sediment was 9.8 d.