Toxicity of aqueous-phase and suspended particle-associated fenvalerate: chronic effects after pulse-dosed exposure of Limnephilus lunatus (Trichoptera).

Non-point source pollution of agricultural surface waters via spray drift and runoff can lead to different short-term exposure scenarios: contamination with water-dissolved or particle-associated pesticide. To compare water-dissolved and particle-associated exposure, fenvalerate (FV) was tested in a 1-h exposure setup with suspended silt particles (5 g dry wt/L; total organic carbon = 3.2%). Chronic effects on the test organism Limnephilus lunatus Curtis (Trichoptera), second and third instar, were observed more than 240 d after transfer of larvae into an outdoor-stream microcosm with pesticide-free water. Significant-effect concentrations were 0.001 microgram/L in water and 0.2 microgram/kg in suspended sediments. Toxicity is lower in the presence of suspended particles by factors between 100 (using mortality and production of biomass as endpoints) and 10 (using emergence pattern and dry wt of adults as endpoints). Effect levels were generally lower than those in previous studies using older larval stages. The reduction of adult dry weight may diminish reproductive success. Aqueous-phase contamination caused lethal and sublethal effects at concentrations of FV that can be measured in the field. In contrast, levels of particle-associated FV that are relevant to the field situation elicited only sublethal responses in the present experiment. Results from this study suggest that short-term FV contamination at expected, field-relevant levels may lead to long-term effects even if the chemical is associated with suspended particles.