Soil contamination near a former Zn-Pb ore-treatment plant: Evaluation of deterministic factors and spatial structures at the landscape scale

Historical soil contamination within a 3 km radius of a former ore treatment plant was evaluated. A total of 247 topsoil samples were collected in a stratified random sampling design taking into account three factors: land use (LU), soil type (ST) and wind direction (WD). Concentrations of trace elements (Cd, Co, Cr, Cu, Ni, Pb and Zn) and major elements (Ca, Mg, K, Fe, Al, Mn) as well as various soil properties (pHwater, pHKCl, TOC and N) were measured. Total Cd, Pb and Zn concentrations were higher than typical background values. Enrichment factors for these three metals were, respectively, 260, 77.4 and 35.5. Principal components analysis (PCA) and factor analysis segregated anthropogenic contamination as a premier factor in influencing concentrations, followed by a second lithogenic factor. The anthropogenic origin of substantial contamination was confirmed though mapping of sample locations relative to contaminant sources. Factor 1 (26.5% of the variance) impacts a large area around the contaminated site and is also indicative of WD influence. Factor 2 (23.9% of the variance) is naturally linked to the local lithology and geology. LU and soil fertility are, respectively, represented by factor 3 (16.5% of the variance), which is linked to pH, and factor 4 (9.3% of the variance), related to organic content. The significance of landscape factors in the spatial distribution of metallic trace elements (MTE) was assessed with an ANCOVA using “distance to the source” as a covariate. Results of the analysis support the hypothesis that Cd, Cu, Pb and Zn concentrations are mainly driven by anthropogenic factors, specifically historical industrial activity at the former ore treatment plant. The ANCOVA also provides a means to quantify the impact of LU and ST as well, particularly on MTE availability in soils. The presence of MTE in soil poses known, and potentially significant, risks to both human health and the environment