Geochemical Characterisation and Pollution Indices of Agricultural Soils Around Coal Mining Sites in Enugu State, South East Nigeria

Coal mining operations, both historical and ongoing, in Enugu State have generated mine waste tailings, acid mine drainage, and atmospheric particulate deposition that have potentially altered the geochemical baseline of surrounding agricultural soils, yet comprehensive post-mining geochemical assessments are lacking for this economically significant region. This study characterises the geochemical composition and calculates pollution indices for agricultural soils collected from three distances (50, 200, and 500 metres) from active and abandoned coal mine sites in three local government areas of Enugu State, South East Nigeria. Major element oxides (silicon dioxide, aluminium oxide, iron oxide, calcium oxide, magnesium oxide, titanium dioxide, potassium oxide, sodium oxide) are determined by X-ray fluorescence spectrometry. Trace element concentrations (lead, arsenic, mercury, chromium, cobalt, nickel, vanadium, and selenium) are measured by inductively coupled plasma mass spectrometry following total acid digestion. Soil pH, cation exchange capacity, total organic carbon, sulphate, and acid-generating potential are also measured. Pollution assessment employs geo-accumulation index, enrichment factor, contamination factor, degree of contamination, and ecological risk index calculations using regional geochemical background values derived from unaffected reference soils. Principal component analysis and cluster analysis identify geochemical associations attributable to mining-derived versus natural lithogenic sources. Findings directly address a critical knowledge gap in the geochemical impact of coal mining on agricultural land use sustainability in the South East geopolitical zone. Keywords: geochemical characterisation, coal mining, agricultural soils, pollution indices, Enugu State