HEAVY METALS DISTRIBUTION IN SEDIMENTS AT ARRESINAL REFINERY SITE IN OMUMA LOCAL GOVERNMENT AREA

Artisanal refinery activities have become a significant environmental concern in crude oil-producing regions of Nigeria, particularly in Omuma Local Government Area. These informal refining operations often lack proper waste management systems, leading to the release of toxic substances including heavy metals into surrounding water bodies and sediments. This study was carried out to assess the distribution, concentration levels, and potential ecological risks of heavy metals in sediments collected from an artisanal refinery site in Omuma LGA. Sediment samples were collected from five different sampling points at increasing distances (0 to 500 meters) from the active refinery point, following standard environmental sampling protocols. Control samples were collected from a non-impacted area approximately 2 kilometers away from the refinery site. The sediment samples were air-dried, sieved, and digested using standard acid digestion methods. Heavy metals including lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), zinc (Zn), and copper (Cu) were analyzed using Atomic Absorption Spectrophotometry (AAS). Pollution indices such as Contamination Factor (CF), Degree of Contamination (Cdeg), and Pollution Load Index (PLI) were calculated to determine the extent of sediment contamination. The results revealed significantly elevated levels of heavy metals in sediments collected near the refinery site compared to control samples. Lead concentrations ranged from 2.34 to 8.76 mg/kg, cadmium ranged from 0.45 to 1.89 mg/kg, and chromium ranged from 1.23 to 4.56 mg/kg. Nickel, zinc, and copper were also detected but at relatively lower concentrations. A clear decreasing trend in metal concentrations was observed with increasing distance from the refinery point, indicating that the refining activities are the primary source of contamination. The Pollution Load Index values indicated moderate to high contamination levels within the first 100 meters of the refinery, while areas beyond 300 meters showed low to moderate contamination. In conclusion, this study confirms that artisanal refinery activities in Omuma LGA have resulted in measurable accumulation of toxic heavy metals in sediments, particularly lead, cadmium, and chromium. These metals pose potential ecological risks to aquatic organisms and may enter the food chain, ultimately affecting human health through consumption of contaminated water and aquatic species. It is recommended that regulatory agencies enforce stricter controls on artisanal refining operations, establish routine environmental monitoring programs, and implement sediment remediation strategies in impacted areas. Public health awareness campaigns should also be conducted to inform local communities about the risks associated with heavy metal exposure from refinery-related pollution.