A comparative analysis of trace metal pollution parity between sandy and shaly soils: Evidence from two mechanic villages in the Imo River basin

Heavy metal enrichment parity in sandy and shaly mechanic village (MV) soils was studied in order to explain the technical and economic imperatives of setting an environmentally friendly MV on either soil. Okigwe (shaly) and Nekede (sandy) mechanic village soils in the Imo River basin Nigeria were tested and compared. Spectroscopic analysis of the soil samples collected from three surface layers (L), where L1: 0-10 cm; L2: 10-20 cm and L3: 90-100 cm shows that Pb > Cu > Mn in the Okigwe MV, and Mn > Pb > Cu in the Nekede MV. Mean concentration of metals (mg kg^-1) in Okigwe MV are Fe: 51,291 ± 18,148, Ni: 22 ± 4, Cd: 20 ± 3, Pb: 500 ± 513, Cu: 616 ± 369, Cr: 16 ± 9, and Mn: 378 ± 207. Similarly, Nekede MV has 22,101 ± 7,273 of Fe; 8 ± 0.8 of Ni; 11 ± 4 of Cd; 320 ± 122 of Pb; 265 ± 145 of Cu; 11 ± 2 of Cr; and 350 ± 191 of Mn. Pollution factor (Pf): Okigwe MV has 0.77, and Nekede has 0.68. Pollution degree: Okigwe MV is greater in L1 and L2, while Nekede is greater in L3, with greater potentials for Pb, and Mn mobility than the Okigwe. Both have similar trends of metal distribution, and significant correlation with their background values. Low clay-silt content in Nekede MV soil suggests low sorption capacity, whereas the high claysilt content (47-64%) of the Okigwe soil suggests lower bioavailability. Infiltration basin is not recommended in a MV on sandy soil if water table is near surface. In such case, the MV must be moved to a location where water table is[37 m, or have clay-shale material transported to the site to form impervious layer base for detention basin. For groundwater safety and sustainability, shaly soils are most recommended for MVs so that detention basin could be economically used for storm water treatment.