Pollution Load Assessment of Tannery Effluents and Their Impact on the Challawa River in Kano State, North West Nigeria

Tannery operations in Kano State discharge chromium-laden and high-organic-load effluents into the Challawa River, posing documented risks to aquatic ecosystems and downstream water users in one of northern Nigeria's most industrially concentrated river corridors. This study assesses the pollution load of tannery effluents and their impact on the Challawa River through a combination of effluent sampling at discharge points and river water quality monitoring at upstream and downstream stations. Effluent parameters measured include pH, total chromium, trivalent and hexavalent chromium, total suspended solids, biochemical oxygen demand, chemical oxygen demand, sulphide, and total dissolved solids. River water monitoring includes all effluent parameters plus dissolved oxygen, biological diversity index using macroinvertebrates as bioindicators, and sediment chromium accumulation by acid digestion and atomic absorption spectrophotometry. Results are compared against Federal Environmental Protection Agency effluent limits and National Environmental Standards and Regulations Enforcement Agency freshwater quality criteria. Pollutant load calculations are performed by integrating effluent flow rates with concentration data. Statistical comparisons between upstream and downstream stations are conducted using independent-samples t-tests and Mann-Whitney U tests for non-parametric data. Findings are expected to demonstrate significant chromium loading and dissolved oxygen depletion at downstream monitoring points. A professionally structured pollution control recommendation report is produced for tannery management and regulatory bodies in Kano State. Keywords: tannery effluent, chromium pollution, Challawa River, Kano, pollution load assessment