FATE OF CHLORPYRIFOS IN OUTDOOR POND MICROCOSMS AND EFFECTS ON GROWTHAND SURVIVAL OF BLUEGILL SUNFISH

Three series of outdoor pond microcosms were treated with the organoph osphorous insecticide chlorpyrifos to determine the fate of this compo und and its ecological impact on an aquatic community. A variety of ap plication regimes were used, including a one-time surface spray, three soil-water slurry applications, and combinations of spray and slurry applications. Maximum chlorpyrifos concentrations in microcosm water r anged from 0.03 to 2.58 mu g/L. Chlorpyrifos disappeared rapidly after each spray application, probably due to volatilization from surface w ater, with an initial half-life of about 1 d. In slurry-treated microc osms, and in spray-treated microcosms after initial volatilization, ha lf-lives in water were consistently around 6 d. A small fraction (gene rally less than 10%) of the chlorpyrifos applied went to the sediment, where it was more persistent than in the water column. The mean lengt h and weight of individual bluegill sunfish (stacked as juveniles befo re chlorpyrifos application) were unaffected by chlorpyrifos exposure. Survival and total biomass of bluegill were reduced in microcosms exp osed to the highest chlorpyrifos concentrations. The inhibition concen trations (IC25) for bluegill survival and total biomass were about 0.4 to 1.9 mu g/L, based on maximum measured concentrations or maximum 96 -h average concentrations. Bluegill survival and total biomass were un affected by repeated exposures to chlorpyrifos if the maximum concentr ations remained below these levels.