Geochemical Signatures and Waste-Soil Interactions of Heavy Metals in Open Dumpsite Soils: Implications for Contaminant Dynamics and Soil Health

Abstract

This work investigated the physicochemical characteristics, heavy metal concentrations, and depth-release properties of soils impacted by the deposition of automechanic (A), paint-processing (P), and abattoir (AB) waste in a coastal milieu in Southern Nigeria. Composite soil samples were collected directly beneath the waste piles at various subsurface depths to assess the vertical distribution and mobility of heavy metals within the waste-impacted soils. The samples were analyzed for their pH, electrical conductivity, organic carbon, organic matter, total nitrogen, available phosphorus, exchangeable calcium, exchangeable magnesium, exchangeable acidity, effective cation exchange capacity, and base saturation. The samples were also analyzed for their aqua regia-extractable concentrations of Lead (Pb), Cadmium (Cd), Chromium (Cr), Nickel (Ni), and Vanadium (V). The results indicated that waste inputs significantly altered the chemical characteristics of the soil, producing significant shifts in soil physicochemical properties. Maximum concentrations of Pb (3918 mg/kg), Cd (116.5 mg/kg), and Ni (226.1mg/kg) were recorded in soils impacted by automechanic wastes, while maximum concentrations of Cr (511.0 mg/kg) and V (179.3mg/kg) were recorded in soils impacted by paint wastes. These concentrations exceeded international guideline limits for residential soils and indicated severe anthropogenic contamination. Measures of contamination factor (CF) indicated severe and widespread heavy-metal contamination across all sites. Heavy Metal Release Percentage (HMR) indicated a vertical gradient in metal release, with the highest percentages of metals released within the topsoil (0-20cm), with attenuation occurring with depth. Overall, these results indicate that indiscriminate disposal of activity-specific wastes has degraded soil quality at the study sites and poses a threat to underlying groundwater resources. Enforcement of stringent waste management regulations, recycling at source, and phytoremediation of contaminated soils are recommended to mitigate further contamination.