Assessment of heavy metals contamination in urban topsoil from Changchun City, China

Due to the rapid urbanization and industrialization that has occurred in China over the last few decades, metals have been continuously emitted into the urban environment and now pose a serious threat to human health. Indeed, there is a growing concern over the potential for pollution of urban soils with heavy metals. Therefore, an extensive soil survey was conducted in urban areas of Changchun, China, to evaluate the current status of heavy metal contamination in soils and to evaluate its potential sources. A total of 352 samples of urban soils were collected from urban areas of Changchun using a systematic sampling strategy in which one sample per km2 was taken (0 ~ 20 cm). The levels of Cu, Pb, Zn and the major elements (Mn, Al2O3, CaO, Fe2O3, MgO, SiO2, K2O and NaO) were then determined by X-Ray fluorescence spectrometry (XRF), while the level of Cd was determined by graphite furnace atomic absorption spectrometry (GF-AAS), and the Hg and As concentrations were determined by atomic fluorescence spectroscopy (AFS). The results indicated that, when compared with the background values of topsoil in the Changchun region, the topsoil in urban areas were enriched with metals, particularly Cu, Cd, Zn, Pb and Hg. The results of correlation coefficient analysis showed that Hg, As, Cd, Cu, Pb and Zn were significantly positive correlated with each other, while Cr and Mn formed another group. Moreover, significantly positive correlations were observed between pH and Zn, Pb, Cu, Cd, As and Hg, indicating that pH influences the distributions of these metals in urban soils in Changchun. Principal component analysis (PCA) was conducted to identify sources of heavy metals and the results revealed distinctly different associations among the trace metals and the major elements in the urban soils. The concentration of Cr appeared to be controlled by the parent material (natural sources), while Cu, Pb and Zn were mainly from vehicle emissions, with Zn primarily coming from vehicle tires. Additionally, Hg and As primarily originated from coal combustion, while Cd was mainly associated with industrial sources. According to the pollution index (PI) of each metal, the overall levels of metal pollution were not especially high, but there were clearly contaminated sites concentrated in the central and northeast portion of the studied region. The Nemerow integrated pollution index (NIPI) of the seven metals also indicated that urban soils in Changchun city were classified as having low level of pollution.

Research Highlights
► The article is an original contribution as a case study, as it is a study of the Changchun city (China) where the soils contamination situation has not been previously studied.
► The present study was conducted to: (1) determine the concentration of heavy metals in urban soil collected from Changchun; (2) identify their natural or anthropogenic sources by principal component analysis (PCA); and (3) assess the level of heavy metal contamination in the topsoil based on pollution index (PI) values and the Nemerow integrated pollution index (NIPI). This information will be helpful to urban planners and environmental risk managers who seek to encourage responsible, environmentally friendly economic development strategies.
► The methods followed in order to reach the aims of the study were basic statistical parameters calculation, binary correlations matrix, Principal Components Analysis, calculation of pollution index (PI) for each metallic element and finally an integrated pollution index (Nemerow Index). The main conclusions are that the core of Changchun city shows a low to middle level of pollution, which is mainly related to traffic and industrial sources.