Assessment of the impact of Asunle dumpsites on water quality of river Asunle, Ile-Ife, Nigeria

Water is an essential resource for sustaining all forms of life on Earth; however, poor environmental management remains a significant challenge that affects water quality. Although several studies have examined the effects of dumpsite leachate on water resources in Nigeria, the Water Quality Index (WQI) approach has not previously been applied to assess the pollution status of River Asunle. This study therefore evaluated the impact of leachate from the Asunle dumpsite on the physicochemical properties and overall quality of River Asunle, Osun State, Nigeria. Eighty-four (84) water samples were collected bi-monthly between February 2018 and December 2019 from seven sampling stations: one upstream, one at the leachate discharge point, and five downstream. Standard analytical methods in accordance with the 2012 American Public Health Association guidelines were used to analyze temperature, turbidity, pH, electrical conductivity (EC), total dissolved solids (TDS), dissolved oxygen (DO), biological oxygen demand (BOD₅), alkalinity, hardness, nutrients, and major ions, while heavy metals (Pb, Cd, and Fe) were analyzed using a Spectra 220 Atomic Absorption Spectrophotometer (AAS). Data were subjected to ANOVA and multivariate statistical analyses, while WQI was computed using the weighted arithmetic index approach. Results showed significant spatial variations across sampling points (p < 0.05). Turbidity increased from 4.53 ± 0.08 NTU (upstream) to 9.42 ± 0.06 NTU (leachate point), exceeding the WHO limit of 5 NTU. DO decreased from 9.37 ± 0.06 mg/L to 2.60 ± 0.00 mg/L, while BOD₅ rose from 3.20 ± 0.11 to 6.10 ± 0.16 mg/L. Lead concentrations exceeded the WHO and NESREA permissible limit of 0.01 mg/L, while cadmium levels were above the WHO guideline value of 0.003 mg/L. In addition, iron concentrations (0.78–0.80 mg/L) exceeded the WHO guideline value of 0.3 mg/L and the NESREA standard of 0.5 mg/L. The mean WQI (77.13) indicated very poor water quality, suggesting that the river is unsuitable for domestic consumption without treatment. Further investigation is recommended to assess its suitability for irrigation and other specific human uses. The study concludes that leachate inflow from the Asunle dumpsite severely degrades River Asunle, posing ecological and public health risks.