Fate of chlorpyrifos in outdoor pond microcosms and effects on growth and survival of bluegill sunfish

Three series of outdoor pond microcosms were treated with the organophosphorous insecticide chlorpyrifos to determine the fate of this compound and its ecological impact on an aquatic community. A variety of application 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 ranged from 0.03 to 2.58 micrograms/L. Chlorpyrifos disappeared rapidly after each spray application, probably due to volatilization from surface water, with an initial half-life of about 1 d. In slurry-treated microcosms, and in spray-treated microcosms after initial volatilization, half-lives in water were consistently around 6 d. A small fraction (generally less than 10%) of the chlorpyrifos applied went to the sediment, where it was more persistent than in the water column. The mean length and weight of individual bluegill sunfish (stocked as juveniles before chlorpyrifos application) were unaffected by chlorpyrifos exposure. Survival and total biomass of bluegill were reduced in microcosms exposed to the highest chlorpyrifos concentrations. The inhibition concentrations (IC25) for bluegill survival and total biomass were about 0.4 to 1.9 micrograms/L, based on maximum measured concentrations or maximum 96-h average concentrations. Bluegill survival and total biomass were unaffected by repeated exposures to chlorpyrifos if the maximum concentrations remained below these levels