Seasonal Dynamics and Pollution Load Assessment of Industrial Effluents: A Case Study of Kano Metropolis, Nigeria, West Africa

Industrialization in rapidly growing urban centers has intensified environmental concerns, particularly regarding the discharge of untreated or poorly treated effluents into aquatic systems. This study evaluates the seasonal dynamics and pollution load of industrial wastewater within Kano metropolis, Nigeria, with emphasis on physicochemical characteristics and associated health risk implications. Wastewater samples were collected from twelve industrial discharge sites during both wet and dry seasons, covering influent, effluent, upstream, and downstream points. Standard analytical methods were employed to determine key parameters including pH, electrical conductivity, total dissolved solids (TDS), alkalinity, sulphate, phosphate, dissolved oxygen (DO), biochemical oxygen demand (BOD), and chemical oxygen demand (COD). Results revealed significant spatial and seasonal variations in wastewater quality. While some parameters such as TDS and temperature largely remained within permissible limits, others—including conductivity, alkalinity, phosphate, and COD—frequently exceeded recommended standards, particularly during the wet season. Elevated conductivity and alkalinity values indicate high ionic and buffering capacity of the effluents, while excessive COD levels reflect substantial organic pollution loads. Notably, certain sites (especially Sites 10, 11, and 8) exhibited extreme contamination, with COD and phosphate concentrations far surpassing allowable limits. Seasonal influence was evident, as wet season samples showed increased pollutant concentrations at several sites, likely due to runoff and enhanced mobilization of contaminants. Health Risk Index (HRI) analysis further demonstrated that alkalinity and COD were the dominant contributors to environmental and human health risks across the study area. Several sites recorded HRI values significantly greater than unity, indicating high to extremely high-risk levels. Site ranking based on overall HRI identified Site 10 as the most polluted, followed by Sites 11 and 8, while Sites 3 and 9 showed relatively low risk. The findings highlight critical environmental challenges associated with industrial effluent discharge in Kano metropolis and underscore the need for stricter regulatory enforcement, improved wastewater treatment practices, and continuous monitoring. This study provides valuable baseline data for environmental management and policy formulation aimed at mitigating industrial pollution and safeguarding public health.