Spatial Distribution of Magnetic Properties and Selected Heavy Metals in Calcareous Soils as Affected by Land Use in the Isfahan Region, Central Iran

Anthropogenic activities have caused the accumulation of heavy metals in the soil environment. Pollution of the soils significantly reduces environmental quality and affects human health. In many recent studies, magnetic susceptibility measurements have been used for pollution monitoring. The objective of this research was to determine the spatial variability of magnetic properties and selected heavy metals and the effect of land use on their variability in the surface soils of the Isfahan region, Central Iran. A total of 158 composite surface (0–5 cm) samples of calcareous soils were collected from an area of about 700 km², located along a cross-border transect from Isfahan City to a steel plant, covering urban, industrial, agricultural, and uncultivated land uses. Concentrations of copper (Cu), zinc (Zn), lead (Pb), manganese (Mn), iron (Fe), nickel (Ni), chromium (Cr), and cobalt (Co) and magnetic parameters, magnetic susceptibility at low frequency (χlf), natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and isothermal remanent magnetization at the field of 100 mT (IRM ₁₀₀ₘT) and the backfield of 100 mT (IRM-₁₀₀ₘT), were measured in all the soil samples. Results showed that magnetic susceptibility in the urban and industrial land topsoils (0–5 cm) samples was significantly higher than that in the agricultural and uncultivated land soils in the study area. Concentrations of Cu, Zn, Pb, Mn, and Fe were positively correlated with magnetic properties (χlf, IRM₁₀₀ₘT, SIRM, IRM-₁₀₀ₘT, and NRM), which could be attributed to their inputs from traffic emissions and industrial activities at the study sites. Ni and Cr concentrations showed significant negative correlations with magnetic properties. No significant correlation was found between Co concentration and magnetic parameters. The Tomlinson pollution load index (PLI) showed significant correlation with the magnetic properties (χlf, IRM₁₀₀ₘT, SIRM, IRM-₁₀₀ₘT, and NRM). The spatial distribution of the selected heavy metals and χlf in the study area suggested that activities at the urban and industrial land sites caused greater pollution as compared to that at the study sites of other land uses. The concentrations of Cu and Zn seemed to have been affected by anthropogenic sources, whereas Ni, Cr, and Co were mainly controlled by natural sources in the study area. Moreover, the concentrations of soil Pb and Fe in the study area could be affected by both lithologic and anthropogenic sources. The magnetic parameters appeared to be a proxy measure for the degree of heavy metal contamination and could be a potential method for the detection and mapping of contaminated soils.