Vertical distribution characteristics and source apportionment of heavy metals in soils of a coking plant site

Coking production is one of the important sources for heavy metal pollution in soils. To investigate the vertical distributions and sources of heavy metals in soils of a decommissioned coking plant site in Pingxiang city. Samples were collected from different depths to analyze contents of seven heavy metals, including As, Cd, Cr, Cu, Ni, Pb and Zn. Sources of there heavy metals were identified and quantified using correlation analysis, principal component analysis, and Positive Matrix Factorization (PMF) model. The results revealed that the average concentrations of As, Cd, Cr, Cu, Ni, Pb, and Zn were 30.72, 1.5, 113.85, 32.62, 37.95, 26.99, and 109.54 mg·kg−1, respectively. All heavy metals had contents exceeding the soil background values of Jiangxi Province with an exception of Pb. Among them, As, Cd, Cr, and Cu exhibited a high variation degree, while Ni, Pb, and Zn showed a moderate variation degree. Generally, contents of there heavy metals showed an initial decrease and then increased progressively vertically, with high values mainly occurring in the upper layers (0—1.5 m). Specifically, the contents of As and Cd were the lowest in the upper middle layer (1.5—3.0 m), and then increased with depth, while the contents of Cr, Cu, Ni, Pb and Zn were the lowest in the lower middle layer (3.0—4.5 m), and then increased with depth as well. The heavy metals in the soils in study area were sourced from industrial activities, traffic-related emissions, and natural background sources. Coal combustion was identified as a main source for As and Ni. Sources of Cd was mainly associated with waste discharge and stacking. Coking industry activities were a main contributor of Cr. Both local and external transportation activities primarily linked to sources of Cu and Zn, and the presence of Pb in soils was mainly attributed to natural factors. The research results of this study could provide guidances and bases for prevention and control of heavy metal pollution in soils and sustainable utilization of land resources in coking plants in China.