Oxidative Damage, Energy Imbalance, and Behavioral Disruptions in Girardia tigrina Exposed to Treated Sewage Effluents

This study assessed the ecotoxicological effects of treated sewage on the freshwater planarian Girardia tigrina, integrating biochemical, energetic, and behavioral biomarkers. Planarians were exposed for 48 h to different concentrations of treated sewage (12.5%, 25%, 50%, and 100%) and compared to controls using commercial water and water from a preserved area (Flona). Exposure to 100% treated sewage caused 100% mortality within 48 h. At sublethal concentrations, biochemical analyses indicated oxidative stress, with increased lipid peroxidation (LPO) at 12.5% and 25%, reduced total glutathione (TG), and elevated catalase (CAT) activity at 25% and 50%. Energetic metabolism was also affected: aerobic metabolism decreased, while anaerobic metabolism increased at 25% and 50%, indicating a shift in energy production pathways under stress. Behaviorally, planarians exposed to 50% sewage showed reduced locomotor activity, and all concentrations delayed photoreceptor regeneration. Despite pollutant levels being below Brazilian limits, several pesticides exceeded European standards, reinforcing concerns about chronic effects of complex mixtures in treated effluents. Biological responses suggested early signs of accelerated aging, with impaired regeneration and mobility. These higher-level effects were preceded by biochemical disturbances, including reduced antioxidant capacity and a shift from aerobic to anaerobic energy metabolism. The rise in anaerobic activity highlights extreme stress at concentrations ≥ 25%. Overall, findings demonstrate that even low concentrations of treated sewage containing pesticide mixtures can cause sublethal but significant effects in non-target organisms. The study underscores the value of planarians as sensitive bioindicators and highlights the urgency of enhancing sewage treatment and regulatory standards to better protect aquatic ecosystems.