From soil sorption to bioaccumulation: Tracing the endectocide ivermectin in soil and earthworms

Ivermectin (IVM), a widely used antiparasitic drug in veterinary medicine, has emerged as an environmental contaminant due to its semi-persistence and potentially harmful ecotoxicological impacts on non-target terrestrial fauna. This study investigates the innovative combination of sorption, desorption, and bioaccumulation dynamics of IVM in soil-earthworm systems, focusing on the species Eisenia fetida, Aporrectodea caliginosa, and Lumbricus terrestris. Sorption experiments in artificial soil (AS) and its components (sand, clay, peat) revealed a strong affinity of IVM for organic-rich substrates, reducing bioavailability and bioaccumulation. Bioaccumulation studies showed that the kinetic bioaccumulation factor BAF_k for IVM in E. fetida ranged from 0.505 to 0.727 g soil dw/g earthworm dw, with elimination kinetics best described by a biphasic model, and suggesting minimal net accumulation. A. caliginosa and L. terrestris showed slightly higher accumulation potential, with accumulation factors exceeding 1 during the uptake phase, although equilibrium was not reached within 21 days. The prolonged accumulation process, combined with a calculated DT₅₀ of 142 days in AS, underscores IVM's potential environmental persistence and risk, particularly its ecotoxicological relevance. The results also suggest that strong sorption to organic matter in soils can mitigate bioaccumulation.