Concentration-time dependent dual toxicity of nano-MoS2 to Eisenia fetida: Remediation at low concentration versus persistent damage at high concentration.

The widespread environmental release of molybdenum disulfide nanomaterials (nano-MoS2) necessitates a rigorous assessment of their ecological risks. The present study systematically investigated the multiscale toxicity of nano-MoS2 to Eisenia fetida. Results showed that although short-term exposure (7 days) to low concentrations of nano-MoS2 (≤ 50 mg/kg) minimally impacted the physiological activities of E. fetida, chronic exposure (28 days) significantly inhibited their growth, reproduction and respiration. In addition, higher concentrations (≥ 200 mg/kg) caused acute mortality, severe growth suppression, and concentration-dependent suppression of macromolecule synthesis. Notably, the toxicity of high-concentration nano-MoS2 toward E. fetida persisted over time without gradual attenuation. Oxidative stress was identified as the primary toxic mechanism, supported by concentration-dependent epidermal and histopathological damage observed via a scanning electron microscope (SEM) and tissue section analysis. Compared to the control, elevated levels of reactive oxygen species and oxidative damage markers (i.e., malondialdehyde (MDA), lactic dehydrogenase (LDH), protein carbonyl (PCO)) were detected, with effects intensifying with both concentration and exposure duration. Antioxidant enzyme activity showed an "inverted U" shaped response to concentration, increasing at low levels but declining under high exposure over time. Metabolomic analysis further indicated that high concentrations (500 mg/kg) suppressed energy metabolism and amino acid synthesis, whereas low concentrations (50 mg/kg) enhanced glycerophospholipid metabolism for membrane protection. These findings demonstrate that nano-MoS2 exhibits concentration-dependent and time-cumulative toxicity, impairing E. fetida viability through oxidative stress-induced structural and metabolic disruption. The identification of a 50 mg/kg toxicity threshold and associated metabolic compensation pathway advances early-warning frameworks for nanomaterial-contaminated soils.