Biomonitoring, physico-chemical, and biomarker evaluations of abattoir effluent discharges into the Ogun River from Kara Market, Ogun State, Nigeria, using Clarias gariepinus.

The discharge of untreated effluents into aquatic ecosystems poses potential adverse effects to aquatic organisms. In this study, the physico-chemical characteristics of abattoir effluent from Kara Cow Market, Ogun State, Nigeria, surface water and sediments from the Ogun River were evaluated. Fish species and macrobenthic fauna diversity in the river were also examined. Acute toxicity and biochemical and histological studies were investigated in Clarias gariepinus exposed to sub-lethal concentrations of the effluent over a period of 28 days. Effluent physico-chemical parameters such as ammonia, conductivity, total dissolved solids, and total suspended solids were higher than set limits. Total polycyclic aromatic hydrocarbons (PAHs) in the effluent and sediment were 6.73 mg/L and 8.07 mg/kg, respectively. Tetracycline (an antibiotic administered to the cows at the market) levels in the effluent and surface water were 0.23 μg/mL and 0.85 μg/mL, respectively. Fish species diversity was lower at the test site compared to the reference site. Chironomus spp. and Tubifex tubifex dominated the benthic assemblage at the test site. There were significant changes (p < 0.05) in the biochemical indices but no histological alterations in exposed C. gariepinus after 28 days. The results demonstrate that the effluent poses potential risks to the aquatic organisms and ecosystem services provided by the river. We recommend that environmental regulatory agencies and stakeholders should establish effluent and solid wastes management systems at the market to prevent environmental and public health epidemics within the framework of the United Nations Sustainable Development Goals 6 (clean water and sanitation) and 14 (life below water). Graphical abstract ᅟ.