Genotoxicity and hematological biomarkers in Mugil sp. from a PAH-contaminated urban estuary in Pernambuco, Brazil

Estuarine ecosystems located in tropical urban regions are increasingly exposed to cumulative anthropogenic and hydroclimatological pressures. This study assessed the environmental health of the Pina Basin estuary (Pernambuco, northeastern Brazil) through an integrated approach combining water quality assessment, polycyclic aromatic hydrocarbon (PAH) monitoring, and biomarker responses in resident mullets (Mugil sp.) during dry and rainy seasons. Physicochemical analyses revealed severe environmental degradation, particularly during the rainy season, when dissolved oxygen levels reached critical hypoxic conditions (0.20 mg L^-1). Although dissolved Σ16 PAH concentrations remained relatively low (<100 ng L^-1), biological responses indicated persistent physiological stress. Micronucleus frequencies showed no significant seasonal variation (0.38% dry; 0.43% rainy; p = 0.719), suggesting chronic and continuous genotoxic exposure throughout the year. In contrast, hematological and biochemical biomarkers exhibited pronounced seasonal responses. Platelet counts decreased significantly during the rainy season (p < 0.001), a pattern associated with handling stress and hypoxia-induced cellular aggregation rather than thrombocytopenia. Rainy-season lymphopenia was accompanied by significant reductions in aspartate aminotransferase activity (p = 0.022) and seasonal variations in protein and lipid metabolism. Multivariate correlation analyses linked these physiological alterations primarily to severe hypoxia, nutrient enrichment, and diffuse urban runoff, rather than to isolated chemical contamination. The findings demonstrate that biomarker networks in wild mugilids are effective early-warning indicators of ecosystem degradation, reflecting the cumulative impacts of urban stressors in tropical estuaries. Integrating physiological and genotoxic biomarkers into environmental monitoring programs is therefore essential for improving coastal management and conservation strategies.