Content area
Abstract
Purpose
Identifying the spatial distribution and degree of heavy metal contamination in the soils is required for urban environmental management. Magnetic measurement provides a rapid means of determining spatial distribution and degree of soil pollution and identifying various anthropogenic sources of heavy metals. The purpose of this study was to characterize the magnetic signature of heavy metal contamination and identify the sources of heavy metals in urban soils from steel industrial city.
Materials and methods
A total of 115 urban topsoils from Anshan city, Northeast China, were collected and determined for magnetic properties and heavy metal concentration. Magnetic susceptibility ([chi]lf) and saturation isothermal remanent magnetization (SIRM) were determined as proxy for ferrimagnetic mineral concentration. Magnetic minerals were identified by using Curie temperature, X-ray diffraction (XRD), and scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). The Pearson' correlation and matrix cluster analyses were used to establish the relationship between magnetic parameters and heavy metal concentrations.
Results and discussion
Urban topsoils exhibit characteristic magnetic enhancement. The magnetic measurement in particle size fractions indicates that 50-2 [mu]m fraction has the highest low-field magnetic susceptibility ([chi]lf), while <2 [mu]m has the highest frequency-dependent magnetic susceptibility ([chi]fd) value. The soil [chi]lf and SIRM values are significantly correlated with the contents of metals (Fe, Pb, Zn, Cu, and Cr) and Tomlinson pollution load index (PLI), which indicates that [chi]lf and SIRM could be served as better indicators for the pollution of heavy metals in the urban topsoil. Spatial distribution maps of [chi]lf, SIRM, and PLI indicate that the pollution hotspots tend to associate with the regions within and close to steel industrial zones. XRD and Curie temperature analyses indicate that the main magnetic minerals of urban topsoils are magnetite (Fe3O4), hematite ([alpha]-Fe2O3), and metallic iron. Magnetic minerals mostly occur in the pseudo-single-domain/multidomain (PSD/MD) grain size range, which is the dominant contributor to the magnetic enhancement of topsoils. SEM observation reveals that magnetic particles in soils exist in irregular-shaped particles and spherule. Results reveal that heavy metals from industrially derived and traffic emissions coexist with coarse-grained magnetic phases.
Conclusions
It is concluded that the magnetic measurement could be regarded as a proxy tool to detect the level of heavy metal pollution and identify the source of heavy metals in urban soils. Magnetic properties provide a fast and inexpensive method to map the spatial distribution of long-term pollution from steel industrial origin on region scale.