Spatial variability of heavy metal contamination and soil physicochemical properties around open dumpsites

Abstract

Open dumpsites are significant sources of soil contamination due to the release of leachates enriched with nutrients and heavy metals. This study evaluated the spatial variability of soil physicochemical properties and heavy metal concentrations around an active dumpsite in Agbala Owerri-West. Soil samples were collected at distances of 0, 50, 100, 200, and 500 m and analyzed using standard methods. Soils were predominantly loamy sand, with sand content ranging from 83.0% to 87.0%, while silt (7.0–9.0%) and clay (6.0–8.0%) were low, indicating high permeability and low retention capacity. Soil pH ranged from 6.3 to 7.7, with higher values near the dumpsite. Organic matter varied from 2.95% to 5.33%, and total nitrogen ranged from 0.08% to 0.28%. Available phosphorus ranged from 13.99 to 27.05 mg kg⁻¹. Exchangeable Ca, Mg, and K ranged from 4.94–28.08, 22.10–56.42, and 0.43–0.61 cmol kg⁻¹, respectively, with peak Ca and Mg at 50 m. Heavy metal concentrations followed the order Hg (2.005–6.016 mg kg⁻¹) > As (0.629–1.379 mg kg⁻¹) > Pb (0.160–0.320 mg kg⁻¹). Mercury showed notable subsurface accumulation, indicating high mobility, while Pb remained relatively immobile. Correlation analysis revealed a strong negative relationship between pH and As (r = –0.72), and between organic matter and Pb (r = –0.70), while Pb correlated positively with clay (r = 0.67) and silt (r = 0.69). The results indicate that the dumpsite enhances soil fertility but also promotes heavy metal accumulation and mobility. This dual effect poses environmental risks, highlighting the need for continuous monitoring and targeted remediation strategies.