Moore_1998_Arch.Environ.Contam.Toxicol_34_152

Laboratory toxicity data contrasting responses of aquatic organisms to insecticides are important for focusing on sensitive species (steepest exposure-response slope) exposed to aqueous concentrations of these insecticides in field studies. These data also allow prediction of expected responses of aquatic species to a range of insecticide concentrations in situ. Aqueous 48-h toxicity tests were performed to contrast responses of Daphnia magna Straus, Hyalella azteca Saussure, Chironomus tentans Fabricius, and Pimephales promelas Rafinesque to acetylcholinesterase-inhibiting insecticides: chlorpyrifos, aldicarb, and chlordane. As expected, invertebrates tested (H. azteca, C. tentans, and D. magna) were >/= 200 times more sensitive than the vertebrate P. promelas to chlorpyrifos exposures. H. azteca was approximately 3.5 times more sensitive to chlorpyrifos (453% mortality/&mgr;g/L) than D. magna (128% mortality/&mgr;g/L). For both aldicarb and chlordane, C. tentans was the most sensitive species tested (2.44 and 2.54% mortality/&mgr;g/L, respectively). Differences in chlordane potency for test species varied only by a factor of approximately 2-3 (0.88% mortality/&mgr;g/L for H. azteca to 2.54% mortality/&mgr;g/L for C. tentans). Although point estimates of population responses such as LC50s, NOECs, and LOECs are of some utility for predicting effects of pesticides in aquatic systems, exposure-response slopes are also useful for extrapolation of laboratory data to diverse field situations, especially where sediment sorption may regulate insecticide exposure or bioavailability.