Aquatic ecotoxicology of the pyrethroid insecticide lambda-cyhalothrin: Considerations for higher-tier aquatic risk assessment

Preliminary risk characterisation for the pyrethroid insecticide lambda-cyh alothrin identifies potential concerns for fish and aquatic invertebrates. Here we describe additional ecotoxicological studies for lambda-cyhalothrin generated to refine the aquatic risk assessment. These include tests condu cted under more realistic exposure conditions (i.e. accounting for the rapi d adsorption of lambda-cyhalothrin to sediments), studies on sediment toxic ity and bioavailability, tests on a range of fish and invertebrate species in order to characterise sensitivity distributions, and field studies which have examined effects on invertebrate communities and fish populations und er semi-natural conditions. Fish are generally less sensitive to lambda-cyh alothrin than are aquatic invertebrates, and fish species tend to be simila r to each other in their sensitivities. Adsorption of lambda-cyhalothrin re duces exposure and hence the apparent toxicity of the compound to fish, and under field conditions no adverse effects on fish have been observed even at concentrations approaching the water solubility. For aquatic invertebrat es, there is a wider range of sensitivities, with the Crustacea and Insects predictably being the more sensitive taxa. Again, adsorption reduces the e xposure of the chemical, and under field conditions no ecologically adverse effects have been observed at concentrations of c.0.02 mu g litre(-1). (C) 1998 Society of Chemical Industry.