Geo-accumulation Index of Heavy Metals in River Ogu Water Sediment in Onne Area, Southern Nigeria

Abstract This study examined the accumulation of contaminants in Ogu River sediments, primarily caused by illegal bunkering activities occurring along the watercourses and riverbanks. Additionally, the operations of local refinery operators and other significant chemical and petrochemical industries in the area significantly contribute to the contamination of aquatic ecosystems. This research focuses on understanding the extent of the contamination and associated risks. The concentration of heavy metals in river sediments was represented by the geo-accumulation index values collected during a study to assess heavy metals in river Ogu water sediment, with a total of 11 samples taken from the Onne area. Atomic absorption spectrometry (AAS) and X-ray fluorescence spectroscopy (XRF) were used to analyze the presence of nickel (Ni), copper (Cu), mercury (Hg), lead (Pb), zinc (Zn), cadmium (Cd), arsenic (As), and chromium (Cr). The relative abundances of these heavy metals in the river sediments decreased in the following order for both seasons: Cadmium (Cd), Copper (Cu), Chromium (Cr), Mercury (Hg), Lead (Pb), and Arsenic (As). The wet season generally had higher mean concentrations than the dry season. Four elements, Zn, Cd, Ni, and Cu, exceeded the tolerable limits set by the Federal Ministry of the Environment. These heavy metals are associated with the Onne refinery, Onne waste dump, runoff from roadside soils, acidic precipitation, and effluents from petrochemical industries. This study is also important in aiding relevant authorities in setting priorities for resource management and policy implementation.