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Ecotoxicological effects of polyethylene microplastics on earthworms (Eisenia fetida) in tetracycline-contaminated soil: Oxidative stress, intestinal barrier damage, and metabolic reprogramming
Summary
Scientists found that when microplastics and antibiotic residue (tetracycline) mix together in soil, they cause even more damage to earthworms than either pollutant alone — harming their gut tissue, disrupting their energy production, and overwhelming their natural defense systems. Since earthworms are a key indicator of soil health, and soil health underpins the food we grow, this suggests that the growing combo of plastic waste and antibiotic pollution in farmland could pose bigger risks to ecosystems (and potentially our food supply) than scientists previously realized by studying these pollutants separately.
The widespread use of antibiotics and plastics has intensified the co-contamination of tetracycline (TC) and polyethylene (PE) microplastics in agricultural soils, yet how PE modulates the toxic effects of TC on soil organisms remains insufficiently understood. Therefore, this study examined how PE modulates TC-induced toxicity in earthworms by exposing them to different concentrations of PE (0.5%, 1%, 2%, 5%, 8%) under TC contamination conditions, combining antioxidant enzyme assays, histopathology, and metabolomic analyses. Results showed that the presence of PE significantly altered TC-induced oxidative stress: superoxide dismutase (SOD) activity declined with increasing PE concentration, reaching the lowest level at TP8 (52.58 U g −1 ); catalase (CAT) activity exhibited hormesis effects, peaking at TP1 (8823.04 U g −1 ); and glutathione S-transferase (GST) activity was significantly suppressed, with the lowest value at TP2 (1.0994 U g −1 ). Histological analysis revealed severe damage to the body wall and intestinal tissues, particularly under TP5 and TP8 treatments, where intestinal epithelium and chloragogenous tissue exhibited marked degeneration and fragmentation. Furthermore, metabolomics revealed marked metabolic reprogramming, characterized by TCA cycle disruption, oxidative stress induction, and altered amino acid flux, ultimately impairing energy metabolism and antioxidant defenses. In addition, key pathways including phenylalanine, tyrosine, and tryptophan biosynthesis; phenylalanine metabolism; and glycerolipid metabolism were significantly affected, suggesting impaired energy metabolism, antioxidant defenses, and osmotic regulation. Overall, these findings highlight the ecological risks of microplastic contamination in antibiotic-polluted soils, offering important implications for soil ecological risk assessment and pollution management.