Laboratory and field response of Chironomus riparius to a pyrethroid insecticide

Sediment toxicity test and bioassay protocols are currently being standardi sed in order to meet European legislative requirements for product assessme nts and environmental monitoring. Most existing test methods require that s ediment-dwelling organisms are exposed to test substances bound to sediment in test systems with uncontaminated overlying water. These test systems ha ve not been widely compared with responses of field populations under reali stic exposure conditions. In this study, sediment toxicity data generated i n the laboratory were compared with the response of a field population of t he midge Chironomus riparius exposed to the pyrethroid insecticide permethr in. In the field this insecticide was applied to the overlying water column of artificial pond systems to give nominal concentrations of 1, 10, 50 and 100 mu g/L. The field response, as measured by larval density and adult em ergence, was not predicted by bulk sediment chemical concentration, sedimen t toxicity test or laboratory bioassay results. All three measurements unde restimated acute toxic effect. Rather, toxicity to C. riparius in the field was predicted more accurately using a short-term water-only toxicity test. No chronic or sublethal effects due-to sediment-bound permethrin were obse rved. This indicates that the primary route of exposure in the field was pr obably via the water column. Primary routes of exposure are difficult to pr edict a priori for different chemical types until the factors affecting bio availability have been fully elucidated. Until this time, there isa need fo r the validation of predictive sediment toxicity tests and for the measurem ent of in situ biological response in conjunction with sediment chemistry a nd toxicity for environmental monitoring purposes, particularly when ongoin g exposure via the water column is likely. (C) 1999 Elsevier Science Ltd. A ll rights reserved.