Combined toxicity of acetochlor and metribuzin on earthworm Eisenia fetida: Survival, oxidative stress responses and joint effect

Abstract

The overuse of herbicides has been linked to serious environmental problems. However, most related studies have focused on characterizing the effects of single herbicides, whereas relatively few studies have assessed the acute toxicity and physiological effects of combined herbicide exposure. Here, earthworms were exposed to acetochlor- and metribuzin-contaminated artificial soil to examine the toxic effects (including mortality, reactive oxygen species (ROS) levels, antioxidant enzyme activity, and malondialdehyde (MDA) levels) of single and combined exposures, after which the toxicity endpoints were analyzed using fa-CI and IBRv2. The 14 d-LC50 for single contaminated acetochlor and metribuzin were 137.06 (124.43–154.26) and 181.28 (161.63–221.02) mg·kg−1, respectively, whereas the LC50 for the combined stress was 112.06 (90.31–195.03) mg·kg−1. Therefore, combined herbicide exposure was significantly more lethal than the administration of either herbicide alone, and this synergistic effect was confirmed via fa-CI plot analysis. Further, acetochlor and metribuzin co-exposure inhibited the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) while significantly increasing ROS and MDA levels. IBRv2 analysis indicated that acetochlor and metribuzin co-exposure (10.0 mg·kg−1) had the strongest effects on several biomarkers in earthworms. ROS level was the most affected indicator and the largest change trend was observed at 7 days post-exposure. Our findings thus suggest that conducting ecotoxicity assessments based on single contaminants may significantly underestimate the effects of contaminant mixtures. Further, this study provides novel insights into the mechanisms of interaction between environmental pollutants.