Ecotoxicity of chlorpyrifos on earthworm Eisenia fetida (Savigny, 1826): Modifications in oxidative biomarkers

Chlorpyrifos (CPF; O, O'-diethyl-3, 5, 6-trichloro-2-pyridyl phosphorothionate) as an organophosphate compound with moderate toxicity that entered the soil in 1965, is widely used as an active substance of many insecticides. CPF may affect some biochemical mechanisms, particularly through disrupting pro- and anti-oxidant balance and inducing free radical-induced oxidative stress. Expired pesticides, if present in ecosystem, may pose new issues of toxicological concern. In the current study, modifications in the oxidative stress (OS) hallmarks including the content of lipid peroxidation (LPO/MDA) and the activities of antioxidant enzymes catalase (CAT) and glutathione S-transferase (GST) in the whole body extract and total antioxidant capacity (TAC), in the coelomic fluid (CF) of earthworm Eisenia fetida were evaluated spectrophotometrically after exposure to different concentrations (1/20th, 1/10th, and 1/5th of LC₅₀) of fresh and expired CPF for 4 and 8 days. First, LC₅₀ for both fresh and expired CPF were determined by using probit method as ≤192 and ≤ 209 mg/kg dry soil, respectively. Our results also revealed that both fresh and expired CPF could be toxic to earthworms via inducing OS at higher concentrations. Here, CPF-induced OS was determined by a significant elevation (p < 0.05) in LPO content, CAT and GST activities and also a meaningful decrease (p < 0.05) in TAC value. Briefly, CPF may exhibit toxic effects in earthworms in the fresh and expired forms via changing oxidative balance and modifying some biochemical markers in the whole body. Further unraveling is needed to elucidate CPF-related impairments in soil organisms.