Direct and indirect effects of microplastics from agricultural mulch films on terrestrial isopods Porcellionides pruinosus (Crustacea, Isopoda): A comparative exposure study

Microplastic (MPs) contamination in terrestrial ecosystems is an emerging concern, with indirect impacts on soil biota often exceeding direct toxicity. This study examined direct and indirect effects of MPs from agricultural mulch films-low-density polyethylene (LDPE), polybutylene adipate terephthalate (PBAT) and starch bioplastics (starch-based)-on the soil isopod Porcellionides pruinosus. We conducted comparative feeding and mesocosm experiments under environmentally realistic conditions. We analysed toxicological endpoints like survival and weight change, and stress-related markers like total haemocyte count, differential haemocyte count, phenoloxidase PO-like activity, enzymatic assays of acetylcholinesterase, glutathione S-transferase, and electron transport system activity. No acute toxicity was observed; however, soil exposure had a more pronounced effect on P. pruinosus, confirming that indirect impacts via altered soil conditions are stronger than direct dietary exposure. Notably, only bio-based MPs triggered changes in cellular and biochemical stress parameters, while fossil-based MPs had no observable effect. The stress response of P. pruinosus in mesocosm experiments aligned with shifts in microbial respiration, suggesting that soil-mediated effects play a dominant role in organismal stress. These findings underscore the importance of considering indirect pathways in MP toxicity assessments and highlight the suitability of terrestrial isopods for integrating diverse toxicological endpoints and stress markers in both laboratory and mesocosm settings.