Chronic effects of low insecticide concentrations on freshwater caddisfly larvae

摘要

The insecticide load in surface waters does not ordinarily reach concentrations acutely toxic to aquatic fauna. The effects of the low insecticide concentrations typical of natural habitats are still not clear, for they often appear only after relatively long exposure times. To test such a situation, the insecticides lindane and parathion were introduced into a static-with-renewal outdoor aquaria system at concentrations about four and five orders of magnitude lower than their respective 96-h LC50s, and their chronic (about 90 days) effects on the survival rate of freshwater caddisfly larvae were observed. The emergence and hence survival rate ofLimnephilus lunatusCurtis was significantly reduced by lindane at 0.1 ng l−1, a value nearly five orders of magnitude lower than the 96-h LC50. Parathion, with acute and subacute toxicity similar to that of lindane, did not significantly alter the emergence rate of this species. In contrast, this substance did produce a significant reduction in emergence rate of the closely related speciesLimnephilus bipunctatusCurtis at 1 ng l−1, even though this species was significantly less susceptible thanL. lunatusto parathion at high concentrations. We conclude that chronic insecticide exposure can be hazardous to freshwater macroinvertebrates even at unexpectedly low concentrations. The low-concentration effects may depend on both species and substance and therefore cannot be predicted from toxicity data at higher concentrati