Ecological and human health risk associated with potentially toxic metals in water from Ijero mining area, Southwest Nigeria

Ground, surface and mine water samples of the Ijero-Ekiti mining area of Nigeria were assessed for their quality. Also, the ecological and human health risks associated with potentially toxic metals in them were also considered. Sixty samples (30 groundwater, 20 surface water and 10 mine water) were collected during the dry and wet seasons of year 2017. The concentrations of metals in the waters were determined using High-Performance Liquid Chromatography Inductively Coupled Plasma-Mass Spectrometry (HPLC-ICP-MS). Hydrogeochemistry, weathering indices and mineral speciation were used to assess the quality. Indices such as geo-accumulation and contamination factors were used to determine the extent of contamination by metals. Risk assessments were carried out using internationally acceptable methods. Results revealed that the average concentrations of Co Ni, Cr, Cu, Zn, As, Cd, Ba, Pb and Sb in groundwater were 0.04 mg/l, 0.04 mg/l, 0.03 mg/l, 2.94 mg/l, 0.19 mg/l, 0.02 mg/l, 1.93 mg/l, 0.13 mg/l and 0.006 mg/l, while for wet season, it was 0.03 mg/l, 1.03 mg/l, 0.02 mg/l, 1.99 mg/l, 0.83 mg/l, 0.02 mg/l, 0.04 mg/l, 0.59 mg/l, 0.86 mg/l and 0.002 mg/l, respectively. Plagioclase and silicate weathering contributes significantly to the amount of metals in the waters. Waters from this area are moderately to extremely polluted by heavy metals. Ecological risk revealed that metals in water of the area pose medium to high ecological risk aggravated by Cd, Zn and Ni. Hazard index (HI) for both carcinogenic (>1E-4) and non-carcinogenic health (>1) risks were above the recommended limits of USEPA. Oral ingestion and dermal contact with contaminated water are major pathways for non-carcinogenic health risks. Carcinogenic health risks of water from the area were aggravated by Pb. We suggest that mining activities in the area should be properly monitored to avoid an endemic.