Investigation of Heavy Metal Contamination in Soils Near Artisanal Gold Mining Sites in Niger State

Artisanal and small-scale gold mining activities in Niger State, North Central Nigeria, have expanded rapidly in recent years, raising concerns about heavy metal contamination of soils in mining communities and their environs. This study investigates the spatial distribution and concentration of heavy metals including lead, arsenic, mercury, cadmium, and zinc in soils surrounding artisanal mining operations in a selected local government area of Niger State. Composite soil samples were collected at systematic intervals from active mining pits, waste dumps, adjacent farmland, and control sites at increasing distances from mining zones. Aqua regia digestion was performed on all samples, followed by analysis using flame atomic absorption spectrometry. Geo-accumulation indices, enrichment factors, and contamination factors were computed to distinguish geogenic background levels from anthropogenic contamination. Results are assessed against Dutch Soil Remediation Standards and Nigerian Environmental Guidelines and Standards to evaluate contamination severity. The study also documents spatial variability using kriging interpolation to generate contamination maps. Elevated lead and arsenic concentrations in peri-mining soils are interpreted as arising from ore processing using mercury amalgamation and the oxidation of arsenopyrite. Findings are intended to support environmental health interventions by the Niger State Environmental Protection Agency and the National Environmental Standards and Regulations Enforcement Agency. Keywords: heavy metals, artisanal mining, soil contamination, Niger State, geo-accumulation index.