Evaluation and Speciation of Heavy Metals Contamination of Selected Artisanal Mining Sites in Mangu Local Government Area of Plateau State, Nigeria

Abstract

Artisanal (illegal) mining has been reported to have environmental and health effects on the surrounding communities due to heavy metals pollution. The determination of total heavy metal concentration does not reflect the toxicity and bioavailability of the metals. Toxicity and bioavailability of the metals can be achieved by determining the form in which the metal exist in the environment (speciation). This present work evaluated the heavy metals’ {cadmium (Cd), copper (Cu), manganese (Mn), lead (Pb), zinc (Zn) &nickel (Ni)} contamination and the form in which they exist at some mining sites in Mangu LGC, Plateau state, Nigeria. Aqua regia ((HCl + HNO3, 3:1 v/v) was used for total metal concentration while sequential extraction method was used to orderly determine the speciation of the heavy metals. The level of the heavy metals in the digested solutions were determined using Buck Scientific model 210VGP Atomic Absorption Spectrophotometer (AAS). The results divulged that the concentrations of the heavy metals were within the FEPA and WHO recommended permissible limit except Cd and Ni. The values of the metals at Mangu Halle mining site followed the sequence: Mn > Zn > Ni > Pb > Cu > Cd whereas the sequence at Alogwom was Mn > Zn > Pb > Ni > Cu > Cd. The results of the speciation indicated that all metals were bound to the five fractions with the residual fraction dominating except Cd which was bound mostly to the soluble and exchangeable fractions. It could be concluded that the presence of these heavy metals in the mobile fractions, indicate that they could be easily released to the environment from soil. Thus, they are also likely to cause toxicity in the environment. Proper monitoring of the mining activities in the communities was recommended.