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

As an important commercial form of vanadium, vanadium pentoxide (VO) is widely used in various modern industries, and its environmental impacts and ecotoxicity have been extensively studied. In this research, the ecotoxicity of VO to earthworms (Eisenia fetida) in soil was tested by exposure to VO 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 VO exposure. The bioaccumulation factor (BAF) of vanadium pentoxide in the earthworms and soil was also measured to explore the bioaccumulation process of VO in the test period. The results showed that the acute and subchronic lethal toxicity values of VO towards E. fetida were 21.96 mg/kg (LC, 14 days) and 6.28 mg/kg (LC, 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 VO 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 VO did not easily accumulate in earthworms, and the BAF was positively correlated with the exposure time and negatively linearly correlated with the VO concentration in the soil. These results indicated that the bioconcentration and metabolic mechanism of VO 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 VO. The analysis of the integrated biomarker response (IBR) index indicated that the trends of IBR values were positively related to the changing VO concentration, and the IBR index could reflect the organism's sensitivity to the external stimulus of VO. The toxicity of VO is mainly caused by V, 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.