TOXIC EFFECT OF TIRE WEAR PARTICLE-DERIVED COMPOUND 6PPD- QUINONE TO CLARIAS GARIEPINUS (GSH, GPX AND SOD)

Background: N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-quinone or 6PPD-Q), a pervasive transformation product of tire-wear antioxidants, has been identified as a highly toxic contaminant in urban stormwater runoff, responsible for acute mortality in sensitive salmonid fish. However, its sublethal, chronic, and mechanistic toxicity on non-salmonid freshwater species, such as the African Catfish (Clarias gariepinus), remains less understood. Objective: This study investigates the toxic effects of 6PPD-Q on the antioxidant defense system—specifically glutathione (GSH), glutathione peroxidase (GPx), and superoxide dismutase (SOD)—in Clarias gariepinus under sub-chronic exposure. Methodology: Clarias gariepinus fingerlings were exposed to environmentally relevant and higher concentrations of 6PPD-Q [0, 0.5, 1.0, 5.0 g/L] for a period of 28 days under controlled conditions. Liver tissues were analyzed for GSH levels, GPx activity, and SOD activity at 7, 14, and 28 days of exposure.
Results: 6PPD-Q exposure induced significant dose- and time-dependent oxidative stress in C. gariepinus. Initial exposure (days 7–14) resulted in a compensatory increase in SOD and GPx activities and GSH levels. However, prolonged exposure (day 28) to higher concentrations (1.0–5.0 g/L) led to a significant decrease in GSH levels and inhibited GPx and SOD activities, indicating an overwhelming of the antioxidant defense system. Conclusion: The results demonstrate that 6PPD-Q is highly toxic to Clarias gariepinus, inducing severe oxidative stress that disrupts key detoxification pathways. The inhibition of GSH, GPx, and SOD suggest that 6PPD-Q can trigger severe hepatic cellular damage and long-term health risks in this species, necessitating tighter monitoring of tire-derived pollutants in freshwater ecosystems.