• Geochemical speciation and mobility of heavy metals in soils. • Cd and Pb were the major sources of environmental hazards. • Metal mobility generally decreased with depth. • Redox-sensitive activities that govern metal stability in contaminated soils. This work investigated geochemical speciation and mobility of selected heavy metals in soils from municipal waste-disposal systems using sequential extraction and metal mobility indices, the overall aim being to assess the potential risk of these metals and their environmental behavior. Soil samples representing three depth profiles were analyzed to evaluate their metal distribution amongst the six operationally defined geochemical forms: water-soluble (F1), exchangeable (F2), acid-soluble or carbonate-bound (F3), oxidizable (F4), reducible (F5), and residual (F6). The findings showed that Cd and Pb were the major sources of environmental hazards, while V and Ni posed moderate risks under varying geochemical conditions. Metal mobility generally decreased with depth, reflecting surface bioaccumulation and progressive stabilization with depth. Metal mobility indices (MMI) had the sequence Cd > Pb > V > Ni > Cr. Principal component analysis (PCA) revealed that five major components (PC1–PC5) accounted for 91.28% of the total variance. Pearson correlation matrices evaluated the interrelationships between different geochemical forms and selected soil properties. The significance of this work lies in its integrated assessment of metal mobility using sequential extraction and MMI within waste-impacted soils in the region, offering generalizable insights into redox-sensitive activities that govern metal stability in contaminated soils.
Udo et al. (Fri,) studied this question.