Spatial distribution and source of potential toxic elements (PTEs) in urban soils of Guangzhou, China

Abstract

Potential toxic elements (PTEs) in urban soils are of great environmental concern because of their potential long-term effects on human health. A systematic soil geochemical survey was performed across central urban districts of Guangzhou, the largest city in southern China. Surface soil samples (0–10 cm) were collected from 426 sites in order to evaluate the environmental quality of this urban area. Geostatistical and multivariate analysis (principal component, clustering, and correlation) were applied to generate spatial distribution maps of PTEs concentrations as well as identify possible sources of metals. The results showed that PTEs ranged widely in value; Arsenic, Hg, Pb, Cu Zn, Cd, Ni, and Mn ranged from 1.4 to 144, 0.01 to 12.2, 18.5 to 4903, 5.0 to 417, 10.1 to 1795, 0.03 to 2.41, 2.5 to 77.6, and 21.2 to 1286 mg/kg, respectively. Iron ranged from 6.1 to 61.8 g/kg. Soils were enriched with Cd, Cu, Hg, Mn, Pb and Zn as compared with soil background values of Guangzhou. Spatial distribution maps indicated similar distribution patterns of Cd, Cu, Pb and Zn. Urbanization history and industrial activities affected the accumulation of PTEs. Relatively higher concentrations of As, Cd, Cu, Hg, Pb and Zn were found in districts with a longer history of urbanization and industrial activities, such as the Liwan district along the Pearl River in western Guangzhou. This area was the most highly contaminated, whereas the Tianhe, a district with a limited time of development, was the least contaminated. Multivariate statistical analysis showed distinctly different associations among the studied metals; suggesting that Fe, Ni and Mn were predominantly derived from a natural (geological) source; As, Cu, Hg, Pb and Zn from anthropogenic sources; and Cd from both sources. Present PTEs levels were also compared with those reported from other urban areas around world, and results indicate that further studies on assessing both the human and ecosystem risks associated with urban contaminated soils will be necessary.