Ecotoxicity stress and bioaccumulation in Eisenia fetida earthworms exposed to vanadium pentoxide in soil

As an important commercial form of vanadium, vanadium pentoxide (V₂O₅) is widely used in various modern industries, and its environmental impacts and ecotoxicity have been extensively studied. In this research, the ecotoxicity of V₂O₅ to earthworms (Eisenia fetida) in soil was tested by exposure to V₂O₅ at a series of doses, and biochemical response indices, such as the superoxide dismutase (SOD) and catalase (CAT) enzyme activity and malondialdehyde (MDA) content, were analysed to determine the mechanism by which antioxidant enzymes respond to V₂O₅ exposure. The bioaccumulation factor (BAF) of vanadium pentoxide in the earthworms and soil was also measured to explore the bioaccumulation process of V₂O₅ in the test period. The results showed that the acute and subchronic lethal toxicity values of V₂O₅ towards E. fetida were 21.96 mg/kg (LC₅₀, 14 days) and 6.28 mg/kg (LC₁₀, 28 days), respectively. For the antioxidant enzymes, SOD and CAT were synchronously induced or inhibited within the time period, and the enzyme activity had a dose-effect relationship with the V₂O₅ concentration. MDA analysis indicated that lipid peroxidation in earthworms mainly occurred at the early stage and was eliminated slowly in the later stage during the test time. In addition, the BAFs were much less than 1, which indicated that V₂O₅ did not easily accumulate in earthworms, and the BAF was positively correlated with the exposure time and negatively linearly correlated with the V₂O₅ concentration in the soil. These results indicated that the bioconcentration and metabolic mechanism of V₂O₅ in earthworms differed with the different exposure concentrations, and bioaccumulation became balanced after 14-28 days in earthworms exposed to a relatively lower dose of V₂O₅. The analysis of the integrated biomarker response (IBR) index indicated that the trends of IBR values were positively related to the changing V₂O₅ concentration, and the IBR index could reflect the organism's sensitivity to the external stimulus of V₂O₅. The toxicity of V₂O₅ is mainly caused by V⁵⁺, which is also an important factor in formulating guidelines regarding vanadium levels in soil, and the test earthworm species (Eisenia fetida) is a sensitive biological indicator for risk assessments of vanadium oxidation in the soil.