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 (χlf) 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 μm fraction has the highest low-field magnetic susceptibility (χlf), while <2 μm has the highest frequency-dependent magnetic susceptibility (χfd) value. The soil χlf 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 χlf and SIRM could be served as better indicators for the pollution of heavy metals in the urban topsoil. Spatial distribution maps of χlf, 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 (α-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.

Purpose

Southern China is an important agricultural production base, as well as an important mineral resource area. There is a big challenge of heavy metal pollution in the soils of this area. Base on the characterizations of cotton and our present results, we discussed the potentiality to remediate the heavy metal-polluted soils through planting cotton in southern China.

Materials and methods

This paper summarises recent research to provide a better understanding of the status and the causes of heavy metal pollution in southern China, compare the applicability of different remediation methods in this area, evaluate tolerance and accumulation of cotton to heavy metals, and discuss the socioeconomic benefits of cotton planting for remediation of heavy metal-polluted soils.

Results and discussion

Human activity could be causing heavy metal pollution in southern China, as lead pollution is the most prevalent and cadmium pollution is the most severe in this area. Physical and chemical methods are used to remediate the heavy metal-polluted soils in southern China, by which treated polluted soils could not satisfactorily address the problems of economic feasibility, “secondary damage” and “secondary pollution”. The use of plants can green the environment to a certain extent, so the phytoremediation method is widely accepted. Cotton does not reach the standard of hyperaccumulation plants but has a relatively large biomass and shows more excellent tolerance ability and enrichment ability to heavy metals. Especially, the Cd concentration is lower in cotton fibre than in other cotton organs.

Conclusions

Cotton may be a potential crop to ameliorate the heavy metal pollution of farmland in southern China. In addition, cotton remediation combining with multiple repair measures of heavy metal pollution would obtain better repair effect and ecological benefits, and agronomic management practices could also effectively enhance cotton-remedied heavy metal-polluted soils.