Polymer-specific stress responses in planarians exposed to microplastics of similar size

Due to their potential ecological impacts, environmental contamination by microplastics (MPs) has gained significant attention. This study investigated the adverse effects of dietary exposure to three distinct polymer types of MPs with similar size-aliphatic polyurethane (PU), polyethylene-polytetrafluoroethylene composite (PE-PTFE), and high-density polyethylene-polytetrafluoroethylene-alumina nanocomposite (HDPE-PTFE-alumina) on the freshwater planarian Girardia tigrina. Dietary exposure was simulated to assess the effects of MPs on the organisms' defense systems and locomotor behavior. The biomarkers assessed were related to oxidative stress, detoxification, antioxidant capacity, cellular energy allocation, planarian locomotor velocity, physiology, and cholinesterase activity. The exposure to PU MPs induced the most pronounced biochemical alterations, with increased glutathione S-transferase, catalase, cholinesterase activities, energy reserves, and aerobic metabolism. Exposure to HDPE-PTFE-alumina MPs also increased glutathione S-transferase activity and aerobic metabolism while reducing lipid peroxidation. In contrast, exposure to PE-PTFE MPs solely reduced lipid peroxidation. Despite these biochemical shifts, planarian movement and physiology were not significantly affected. This study highlights the need for comprehensive analysis of diverse polymers, physiological endpoints, and exposure routes to understand the ecotoxicological impacts of MPs on model species. Additionally, it underscores that comparing effects across polymer types, even within the same species and size range, can lead to confounding results. The results offer valuable insights for future research on long-term sublethal effects, particularly regarding growth, reproduction, behavior, and redox biology in freshwater planarians.