Neurotoxicity, oxidative stress biomarkers and haematological responses in African catfish (Clarias gariepinus) exposed to polyvinyl chloride microparticles

The aquatic environment is outrageously littered with resin pellets and particles of plastic origin which can jeopardise the health of aquatic organisms. The present study investigated the effect of polyvinyl chloride (PVC) microparticles on blood parameters, leucocytes, lipid peroxidation and antioxidant system (brain and gill) of Clarias gariepinus. C. gariepinus is a fresh water indicator species often used as model for ecotoxicological assay. Fish specimens were exposed to diets spiked with PVC microparticles (95.41 +/- 4.23 mu m) at the following concentrations; 0.50%, 1.50% and 3.0% and control diet for 45 days, followed by a depuration trial which lasted for 30 days. Blood and tissues (brain and gill) were sampled every 15 days interval for haematology, antioxidant enzymes and lipid peroxidation assay. The result obtained revealed that PVC orchestrated the marked alterations in haematological indices. Mean cell volume and mean cell haemoglobin values reduced significantly in all concentration treated groups and were time-dependent. Neutrophil counts decreased with a corresponding increase in PVC exposure time while lymphocytes and monocytes values showed no significant difference between the control and exposed fish groups. Glutathione peroxidase activity was altered substantially in the brain and gill of the exposed groups compared to the control. Superoxide dismutase activity was inhibited in the brain and gill of the exposed groups compared to the control, as well as the different exposed periods. Catalase activity reduced significantly in the brain of 0.5% PVC exposed groups, and also decreased in a time-dependent manner while its activity in the gill did not change significantly among the exposed groups relative to the control. Lipid peroxidation levels in the brain of PVC exposed groups increased significantly in a dose and time-dependent manner. However, PVC caused no significantly change in the gill lipid peroxidation level of the exposed fish, but elevated the lipid peroxidation levels as the exposure time increased. Acetylcholinesterase activity in the brain and gill of the exposed fish reduced substantially with increase in the exposure time. Variations in haematology, antioxidant enzymes, lipid peroxidation and acetylcholinesterase activities are indicative of oxidative stress and neurotoxicity in fish. C. gariepinus is an indispensable bioindicator to measure environmental impact of PVC microparticles.