Heavy Metals in Raw and Treated Water, Sediment, and Fish at the Barekese Reservoir Headworks

Heavy metal contamination in aquatic ecosystems poses a serious threat to both fish and human health. The research evaluated the levels of five major heavy metals, cadmium, lead, arsenic, copper, and mercury, and six physicochemical properties, including temperature, pH, dissolved oxygen (DO), electrical conductivity, salinity, and total dissolved solids (TDSs), in the Barekese Reservoir and its tributaries in Ghana’s Ashanti Region. The study hypothesizes that heavy metal contamination in the Barekese Reservoir and its tributaries varies seasonally and spatially, with some levels exceeding international safety standards. Sampling was conducted over 2 months, representing both wet and dry seasons, using a spatially stratified method. Water and sediment were sampled from three designated zones spanning the reservoir and its connecting tributaries, while fish samples (Coptodon zillii and Sarotherodon galilaeus) were obtained from local fishermen. All samples were analyzed using atomic absorption spectroscopy. Sediment contamination was evaluated using the geo-accumulation index (I-geo), contamination factor (CF), and pollution load index (PLI). Lead, cadmium, mercury, and arsenic in treated water (TW) and in samples from the reservoir and its tributaries were higher than the World Health Organization (WHO)-recommended limits for drinking water, while copper levels remained below permissible limits. In sediments, cadmium and copper concentrations surpassed the USEPA guideline values, whereas lead, arsenic, and mercury levels remained within safe limits. Physicochemical parameters across all sampling points were within WHO acceptable ranges. The I-geo indicated moderate cadmium pollution (1 < I-geo ≤ 2) at the Dam site, Subinso, and tributary sampling points. High CF values were recorded for cadmium, arsenic, and mercury in sediments from the reservoir and tributaries. Arsenic concentrations in fish tissues ranged between 0.03 ± 0.02 and 0.36 ± 0.12 mg kg⁻¹, while mercury levels varied from 2.79 ± 0.37 to 5.50 ± 0.04 mg kg⁻¹, both of which were significantly above the WHO’s recommended limits of 0.01 mg kg⁻¹ for arsenic and 0.004 mg kg⁻¹ for mercury. The findings highlight potential public health risks, recommending awareness creation about consuming contaminated fish and untreated water, and promoting sustainable land use practices in the reservoir’s catchment to mitigate heavy metal pollution.