Impact of clay mining on water quality in Nkanyi, Oyivo and Onye Rivers, Nigeria: seasonal variations in heavy metal contamination and hydrological changes

Abstract

The hydrological effects of the inflow of clay mine water to three river banks were determined. Samples were collected at upstream, midstream, and downstream stations in January, May, and July (24 river-water samples in total, as River Onye was dry in January). Water-quality parameters, including the pH, turbidity, dissolved oxygen and heavy metal concentrations, were assessed over time. The data reveal a major seasonal difference in contamination concentrations. Maximum turbidity (305 NTU) was observed in July, above a limit of 5 NTU as defined by the World Health Organisation. At midstream locations, dissolved oxygen (DO) concentrations decreased to 1.8 mg/L, compared to the World Health Organisation’s suggested 6.5 mg/L, and heavy metals analysis revealed mercury (0.456 mg/L, 22,700% above the WHO guidance) and arsenic (0.013 mg/L, 30% above the WHO guidance) contamination. A two-way ANOVA confirmed a statistically significant seasonal effect (p < 0.05) on mercury and arsenic concentrations.