Pyrethroid effects on freshwater invertebrates: a meta-analysis of pulse exposures

Pyrethroids are widely used insecticides that may seriously harm aquatic organisms. Being strongly hydrophobic, pyrethroids in solution occur only in short pulses but may be retained in sediments for longer periods. Consequently, most studies consider the chronic exposure of sediment dwelling organisms. We collected data from 16 studies to determine effect thresholds for stream macroinvertebrates exposed to short pyrethroid pulses evaluating lethal and sublethal ecologically relevant endpoints. Dose-response models showed EC50 for lethality, functional and behavioural endpoints down to 1/100, 1/100 and 1/1000 of the 48 h LC50 for Daphnia magna, respectively. The results indicate that the overall sensitivity of stream macroinvertebrates to pyrethroids may be higher than previously believed. This review shows the relevance of incorporating data on sublethal endpoints and appropriate post-exposure observation periods in future studies. The current risk assessment procedures and the higher tier approach are discussed in the light of our results.