This work quantitatively evaluates the level and impact of selected physiochemical properties of fertilizer effluent on the Obinna River of Adani, Enugu State, Nigeria. The fertilizer effluent originated from surrounding farms and flushed into the Obinna River. Water samples were collected from designated points along the river and analysed for physical, chemical and biological properties using standard methods of APHA. Impact of selected key parameters such as nitrate, phosphate, manganese, dissolved oxygen, biochemical oxygen demand and heavy metals (lead, iron and manganese), was studied. The results of the parameters were compared with the World Health Organisation (WHO) permissible standard for freshwater. Measured concentrations of phosphate (5.00, 7.21, 3.92 mg/L), manganese (1.53, 1.18, 1.47 mg/L) and lead (18.9, 21.7, 39.7 ppm) were found to be above the WHO standard while nitrate (0.04, 0.03, 0.03 mg/L) and iron (0.001, 0.001, 0.1 mg/L) were within the standard. The mean concentrations of heavy metals increased in the following order: Fe (0.034) < Mn (1.4) < Pb (26.8) from upstream S1 to downstream S3, with manganese and lead being above WHO standard. The results showed a level of significance for the chi-square distribution and correlation coefficients while the analysis of variance (ANOVA) results was conflicting. It could be inferred that the impact of the selected parameters contributed to the pollution of Obinna River.
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