Variation in the Chemical Sensitivity of Earthworms from Field Populations to Imidacloprid and Copper

The chemical risk of pesticides for nontarget soil macroorganisms has mainly been assessed using the compost earthworm Eisenia fetida. However, E. fetida does not occur in agroecosystems, and it is generally less sensitive than other earthworm species. Thus, the extrapolation of its response to pesticides to other earthworm species may lead to uncertainties in risk assessment. Because toxicity data for other earthworms are scarce, we assessed the chemical sensitivity of five species (Allolobophora chlorotica, Aporrectodea caliginosa, Aporrectodea longa, Aporrectodea rosea, and Lumbricus rubellus) from different habitats (forests, wetlands, and grasslands), as well as E. fetida, to imidacloprid and copper in single-species acute toxicity tests. In addition, we examined the relationship between earthworm traits (ecotype and weight), habitat characteristics (ecosystem type and soil pH), and chemical sensitivity. The lower limits of the hazardous concentration affecting 5% (HC5) of species were 178.99 and 0.32 mg active ingredient/kg dry weight for copper and imidacloprid, respectively. Some concentrations that have been measured in European agroecosystems for both pesticides were above the HC5s, indicating toxic risks for these organisms. Furthermore, soil pH from the sampling habitat played a significant role, with earthworms sampled from extremely acidic soils being less sensitive to copper than earthworms from neutral soils. In addition, endogeic earthworms were more sensitive to imidacloprid than epigeic earthworms. This may translate to changes in soil functions such as bioturbation, which is mainly carried out by endogeic earthworms. Our results suggest that risk assessment should include a wider range of earthworms covering different habitats and ecosystem functions to achieve a better protection of the biological functions carried out by these key soil organisms. Environ Toxicol Chem 2023;42:939-947. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.