Tissue-Specific Accumulation of Heavy Metals and Oxidative Stress in Atlantic Bonito (Sarda sarda, Bloch 1793) Marketed in Kütahya

Heavy metal pollution in aquatic environments presents a considerable risk to fish populations, primarily through the induction of oxidative damage. This study aimed to investigate the relationship between heavy metals (Cu, Cd, Hg, and Pb) and As accumulation and oxidative stress biomarkers, including malondialdehyde (MDA), total oxidant status (TOS), and oxidative stress index (OSI), together with antioxidant defenses such as reduced glutathione (GSH) and total antioxidant status (TAS), in the muscle and gill tissues of Atlantic bonito (Sarda sarda, Bloch 1793). Furthermore, human health risks were evaluated using the target hazard quotient (THQ), hazard index (HI), and carcinogenic risk (CR) metrics. Our findings indicate that heavy metals such as cadmium (Cd) and copper (Cu) accumulate significantly more in the gills than in the muscle tissue (p < 0.05). This accumulation seems to cause an unusual biological response, evidenced by a notable increase in oxidative stress markers—namely MDA, TOS, and OSI—within the gill tissues (p < 0.01). Specifically, gill MDA concentrations (5.43 ± 1.86 nmol/mg) were significantly higher than those observed in the muscle tissue (4.07 ± 1.63 nmol/mg). Concerning human safety, both the HI (0.8393) and CR values remained within established safety thresholds. These observations suggest that the gills are the primary site of metal-induced oxidative damage, and the robust correlation between metal accumulation and OSI/MDA levels implies that these parameters are reliable indicators for evaluating aquatic metal pollution.