MARGARET OMOSIGHO EBHODAGHE

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.