Ecotoxicological effects of soil microplastic types and concentrations on earthworms

Microplastics (MPs) pollution in terrestrial ecosystems has raised global concerns due to its potential threats to soil health and biota. This study systematically investigated the ecotoxicological effects of conventional plastic materials (i.e., polyethylene (PE), polypropylene (PP)) and biodegradable (poly(butylene adipate-co-terephthalate) (PBAT)) MPs on the earthworm Eisenia fetida under environmentally relevant concentrations. A 28-day soil incubation experiment was conducted with MPs exposure at 0.05 %, 0.5 %, and 2 % (w/w). Endpoints included survival, growth, reproduction, oxidative stress biomarkers, histopathological alterations (via H&E staining), and the integrated biomarker response (IBR). Results revealed polymer- and concentration-dependent toxicity. While PE- and PBAT-MPs did not significantly affect survival and growth, PP-MPs exhibited a paradoxical dose effect: 2 % PP-MPs caused significant mortality (16.7 %, p < 0.05), whereas 0.05 % PP-MPs stimulated growth (42.1 % increase, p < 0.001). All MPs treatments disrupted reproductive efficiency, increasing cocoon production without corresponding juvenile output. Oxidative stress and tissue damage (epidermis, intestine, and reproductive organs) were observed at 0.5 % and 2 % exposures. Notably, PBAT-MPs induced the highest cellular toxicity, evidenced by elevated 8-hydroxy-2'-deoxyguanosine (8-OhdG, 190.9 ng L^-1) and IBR values, indicating heightened DNA damage and integrative stress. These findings underscore the ecological risks of both conventional and biodegradable MPs to soil invertebrates, emphasizing the need for comprehensive risk assessments that consider polymer-specific toxicity and long-term exposure scenarios.