Comparative toxicity of fresh and expired butachlor to earthworms Eisenia fetida in natural soil: Biomarker responses

Butachlor as a selective pre-emergent herbicide, is mainly used to control the growth and productivity of certain annual grass and broad-leaf weeds. As non-target soil creatures, earthworms are affected detrimentally due to direct contact with pesticides. Our purpose was to compare the changes in the oxidative stress biomarkers in earthworms Eisenia fetida under the exposure of fresh and expired butachlor in the natural soil. LC₅₀ of the fresh/unexpired and expired butachlor were determined by probit analysis amounting ≤440 and ≤ 471 mg/kg dry soil, respectively. Earthworms were then exposed to three sublethal concentrations (1/5th, 1/10th, and 1/20th of LC₅₀) of both fresh and expired butachlor for 4 and 8 days. The level of oxidative stress biomarkers namely lipid peroxidation, glutathione S-transferase, and carbonylated proteins were increased. Besides, the catalase activity and value of total antioxidant capacity in earthworm's caulomic fluid were found to be decreased. In addition, it was clearly showed that butachlor can cause tissue damages in earthworms. The fresh and expired butachlor trigger the onset of oxidative damages as illustrated by altered oxidative stress biomarkers and tissue damages, particularly at the end of 8 days and high concentrations. Contrary to expiration, we found evidence that expired BUC is acutely toxic to earthworms. The fresh BUC was more deleterious than expired one to earthworms. Meanwhile, it must be considered that the regulations towards disposal of expired toxicants must be strictly followed without impairing the soil ecosystem.