Heavy metal distribution trend and speciation in groundwaters within the lower cross river hydrological basin, SE-Nigeria

The environmental effects of potentially toxic metals on a wide range of environmental materials in a wide range of various uses have recently been the subject of extensive research. This research provides information on chosen potentially toxic metals' concentration levels and risk potentials in shallow groundwaters throughout the lower Cross River hydrological basin. The VISUAL-MINTEQ computer program is used in geochemical modeling to find ionic species, their saturation indices, and potential bioavailability. The findings of the chemical analysis reveal that the metals Fe, Mn, Cu, Pb, Zn, Cd, and Cr are present in low concentrations and do not directly threaten the quality of the water. According to modeling, they make up a large portion of the overall ion concentration (roughly 60–90% of all the metals in the groundwater) and are primarily present as free mobile ions. Other ionic species with smaller percentages of contributions to overall ion concentrations include the aqueous carbonates, sulfates, chlorides, and hydroxides of these metals. Only the Fe2 + ionic species recorded oversaturation in the groundwaters within the basement sector of the study area, according to estimated saturation indices, which indicate that the groundwaters are typically undersaturated with metallic species. In some areas of the study region, Mn ions also exhibit low saturation levels. These metals' and their ionic species' low concentrations are ascribed to hydrochemical processes that are constrained by the presence of limiting mineral phases, (carbonates and sulfates). Goethite concentrations that are dominant further restrict the mobility of metal ions, lowering the possibility of groundwater pollution and potential bioavailability.