Long-term ecological risks of prometryn in male marine medaka (Oryzias melastigma): Bioaccumulation, toxicity mechanism, and post-exposure recovery.

Prometryn (Pro) is a triazine herbicide increasingly detected in aquatic environments, yet its long-term effects and post-exposure recovery in marine fish remain poorly understood. We investigated Pro bioaccumulation, toxicity, and recovery in male marine medaka (Oryzias melastigma) following 42-day exposure to 10 and 100 μg/L Pro and 18-day depuration. Pro accumulated rapidly in liver, intestine, and gills, with approximately 80% eliminated within 4 days of depuration and complete clearance by 18 days. Exposure significantly reduced survival and hepatosomatic index and caused histopathological damage across multiple tissues, alongside disrupted antioxidant defenses and increased lipid peroxidation, indicating oxidative stress. Hepatic transcriptomic revealed 5068 differentially expressed genes (DEGs), with enrichment pathways including PPAR signaling, steroid hormone biosynthesis, and cytochrome P450-mediated metabolism, indicating broad metabolic and detoxification disruption. Following depuration, DEGs decreased to 2976, but residual transcriptional activity, oxidative stress markers, and tissue morphology indicated substantial yet incomplete recovery. Notably, rapid elimination preceded the recovery of several biological endpoints, revealing a decoupling between chemical clearance and biological restoration. These findings demonstrate that tissue residue depletion alone may underestimate herbicide-induced effects persistence, highlighting the need of integrating chemical, biochemical, histopathological, and molecular endpoints for evaluating ecological risks and recovery after aquatic contaminant exposure.