Magnetic Properties as Indicators of Cu and Zn Contamination in Soils1

Concentrations of copper (Cu) and zinc (Zn) and various magnetic parameters in contaminated urban roadside soils were investigated using chemical analysis and magnetic measurements. The results revealed highly elevated Cu and Zn concentrations as well as magnetic susceptibility in the roadside soils. The mean concentrations of Cu and Zn in these roadside soils were almost twice those in average Chinese soils, with the mean magnetic susceptibility of the roadside soils reaching about 179 × 10−8 m3 kg−1. This enhanced magnetic susceptibility was attributed to the presence of anthropogenic soft ferrimagnetic particles. A low frequency-dependent susceptibility (2.5% ± 1.0%) observed in the roadside soils indicated the coarse multidomain (MD) ferrimagnetic grains to be the dominant contributor to magnetic susceptibility. The Cu and Zn concentration of the soils had highly significant linear correlations with magnetic susceptibility (P ≤ 0.01), anhysteretic remanent magnetization (P ≤ 0.01), and saturation isothermal remanent magnetization (P ≤ 0.01). This suggested that heavy metals were associated with ferrimagnetic particles in soils, which were attributed to input of traffic emissions and industrial activities. Scanning electron microscopy and energy dispersive X-ray spectra of magnetic extracts of the roadside soils further suggested the link between the magnetic signal and concentrations of heavy metals. Thus, the magnetic parameters could provide a proxy measure for the level of heavy metal contamination and could be a potential tool for the detection and mapping of contaminated soils.