CLARIAS GARIEPINUS

6PPD-quinone (6PPD-Q) is a transformation product of the tyre additive 6PPD. It enters aquatic systems through stormwater runoff and poses an emerging toxicological concern. This study examined the acute and sub-lethal effects of 6PPD-Q on Clarias gariepinus, a freshwater catfish commonly used in ecotoxicological studies. The objective was to determine the sensitivity of Clarias gariepinus to 6PPD-Q and to assess changes in haematological parameters as indicators of physiological stress. Juvenile Clarias gariepinus were exposed under laboratory conditions to a range of 6PPD-Q concentrations for 96 hours to evaluate acute toxicity, followed by sub-lethal exposure for haematological analysis. No mortality was recorded during the acute phase, indicating that the compound did not reach a lethal threshold within the tested concentration range. Sub-lethal exposure produced measurable haematological alterations. There was a significant decrease (P<0.05) in red blood cell count, haemoglobin concentration, and packed cell volume, suggesting anaemia and impaired oxygen transport. White blood cell counts increased, indicating immune response activation. These findings demonstrate that 6PPD-Q affects fish health at non-lethal levels, even when acute mortality is absent. This study highlights the ecological risk posed by 6PPD-Q in aquatic environments. Its persistence and sub-lethal toxicity underscore the need for environmental monitoring and regulation of tire-derived pollutants. Further research should address long-term exposure, tissue accumulation, and population-level impacts in freshwater ecosystems.

One of the most recent and emerging contaminants today, is plastic. These plastics through improper waste disposal and runoff, find their way to water bodies. This plastic when they fragment or occur in very small sizes (<5mm) are termed microplastic. They can be classified on physical characteristics or chemical characteristics. They pose risk to both fish and consumers of the fish. The fish samples were analysed within 24hrs of collection. The fish were digested using 10% KOH, and purified using H2O2. The filtrates were examined under microscope to identify the microplastic particles, which were physically confirmed using the hot needle method and confirmed chemically using Fourier transfer infrared spectroscopy. Microplastics occur at all stations through the three months under study. The microplastics found based on morphological characteristics are pellet, foams, fibre, filaments, and fragments, while on polymer characteristics, there were two namely; polypropylene and polyethene. The type of microplastic prevalent in each station had a relationship to the prevalent economic activities at the watershed. For example, at station 3 (Ikpoba bridge), the
prevalent economic activities at the water fronts are car and rug washes, the prevalent plastic is polypropylene

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.