Heavy Metal-Induced Genotoxic Damage in Chelon auratus: Evidence from a Coastal Gulf Ecosystem

Estuarine and river-influenced coastal ecosystems are recognized as important sinks and channels for transfer of heavy metals into the marine environment. Continuous intake of metal pollutants could create chronic exposure situations, perhaps leading to molecular and cellular damage to resident biota, even if environmental concentrations are within regulatory limits. Thus, the incorporation of molecular and genotoxicity biomarkers into environmental monitoring programs has received growing interest, as changes in gene expression are among the earliest detectable responses to pollutant stress and may precede genotoxic effects, including DNA damage, at higher or prolonged levels of contaminant exposure. The present study aimed to determine the levels of heavy metals in the coastal zone where the Deliçay River flows into the Gulf of Iskenderun in the extreme northeastern Mediterranean Sea, Türkiye, and to investigate the genotoxic effects in the euryhaline ray-finned fish golden grey mullet (Chelon auratus). In this study, seasonal water samples (n = 3 per site per season) and C. auratus specimens (n = 10 per site per season; total n = 80) were collected from a reference site and the Deliçay estuary. Water samples were analyzed for metals (cadmium (Cd), chromium (Cr), iron (Fe), lead (Pb), and zinc (Zn)) and fish samples were analyzed with the micronucleus (MN) test for determining nuclear abnormalities and the comet test for DNA damage levels. The concentrations of Fe, Zn, and Pb in seawater exceeded the Criterion Continuous Concentration (CCC) thresholds during the summer and autumn seasons, as well as in terms of annual mean values, indicating a potential chronic ecological risk to marine organisms. From the results of the micronucleus test performed in the present study, the highest MN frequencies (10.16 ± 0.15%) and other erythrocytic nuclear anomalies [kidney-shaped (10.36 ± 0.32%), binucleated (14.20 ± 0.10%), notched (14.63 ± 0.20%), lobed (15.43 ± 0.11%), and budded (15.33 ± 0.15%)] were found along the studied coastal zone in summer season. Results of the comet test, supporting the micronucleus test results, showed the highest percentages of DNA damage determined in all seasons in the gill and liver tissues of fish sampled in the studied coastal zone. This study is the first to evaluate the effects of heavy metal-induced genotoxic stress on ecological integrity in this coastal zone using a biomarker-based approach, and the results underscore the need for comprehensive environmental monitoring and pollution reduction strategies to protect ecosystem health.