Assessment of toxic effects of thallium on the earthworm Eisenia fetida using the biomarker response index†

Thallium (Tl), though not essential for biological systems, is widely used in industrial activities, resulting in soil pollution and adverse effects on soil biota. Systematic toxicological studies on Tl, especially concerning soil organisms, are relatively rare. This research evaluates the toxic effects of Tl on earthworms by measuring oxidative stress biomarkers, such as superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), malondialdehyde (MDA), and 8-hydroxydeoxyguanosine (8-OHdG), and by assessing the expression of functional genes, such as heat shock protein 70 (Hsp70), metallothionein (MT), and annetocin (ANN). Additionally, this study employs the Biomarker Response Index (BRI) and two-way ANOVA to comprehensively assess the cumulative toxicity of Tl in earthworms. The findings indicate that Tl exposure significantly exacerbates oxidative stress and cellular damage in earthworms, particularly under conditions of high concentration and prolonged exposure. BRI results demonstrate a continuous decline in the physiological state of earthworms with increasing Tl concentration and exposure duration. Two-way ANOVA reveals significant dose-responsive increases in SOD and CAT activities, as well as in ANN gene expression. Apart from GST activity, other biomarkers significantly increased over time, and the changes in biomarkers such as SOD, CAT, MDA, and 8-OHdG were significantly influenced by dose and time. LSD post hoc tests show significant effects of dose, time, and their interactions on all biomarkers except for GST. These findings are valuable for gaining a deeper understanding of the ecological risks of Tl in soil environments and its potential threats to soil biota, aiding in the management of ecological risks associated with Tl-contaminated soils.