Chronic toxicity of ivermectin to the benthic invertebrates Chironomus riparius and Lumbriculus variegatus

Previous studies have shown that ivermectin, a widely used parasiticide, is very toxic to many non-target invertebrate species. In view of the strong binding of ivermectin to sediments and the scarcity of data on chronic toxicity to freshwater sediment invertebrates, chronic effects of the parasiticide on the midge Chironomus riparius and the oligochaete Lumbriculus variegatus were investigated. C. riparius and L. variegatus were exposed for up to 28 days to ivermectin-spiked artificial sediment. Nominal ivermectin concentrations were 3.1 to 50 A mu g/kg dry sediment in the Chironomus test and 50 to 5,000 A mu g/kg dry sediment in the Lumbriculus test. The evaluated endpoints were survival, growth, emergence ratio and development rate for C. riparius, and survival/reproduction and total biomass for L. variegatus. Ivermectin had a significant, concentration-dependent effect on larval survival and growth, emergence and development rate of C. riparius. With a lowest observed effect concentration (LOEC) of 6.3 A mu g/kg dry sediment, larval dry weight was the most sensitive endpoint. L. variegatus was considerably less sensitive to ivermectin than C. riparius. A LOEC of 500 A mu g/kg dry sediment was derived for effects on survival/reproduction and total biomass. The results of the present study, especially the high toxicity of ivermectin to C. riparius, indicate that the potential impact of ivermectin on freshwater benthic invertebrates deserves further attention.