Multivariate geostatistical analysis of heavy metals in topsoils from Beijing, China

Background. Regional soil environmental quality is a hotspot and difficulty in the environmental sciences for the spatial variability of pollutants and the relationship between them. Beijing, the capital of China, has been undergoing a rapid economical development during the past three decades, and thus might encounter the same issues as the developed countries. However, there is little information about the soil environmental quality of Beijing, especially at the regional scale. The real soil environmental situation of heavy metals remains unknown, even less the sources of possible. pollutants. Objectives. The main objectives were to identify the spatial variability and main sources of heavy metals in Beijing soils by conducting multivariate statistical analyses, including geostatistical analysis assisted with GIS tools. These results will contribute to the establishment of the soil quality baseline and the management of regional environment. Materials and Methods. Seven hundred and seventy-three samples of topsoils (0 - 20 cm) were collected from all over Beijing, China. The samples were digested with HNO3 and H2O2. The concentrations of Cr, Cu, Ni, Ph and Zn were analyzed with a FL-AAS and those of Cd with a GF-AAS. The concentrations of As were determined with AFS-2202. Principal component analysis (PCA) and partial correlation analysis (CA) were used and geostatistics was conducted for the data processing. Results. Concentrations of topsoil As, Cd, Cr, Cu, Ni, Ph and Zn in the Beijing area were measured and contour maps were constructed to describe the metals' spatial distribution. Except for the background effect of the soils, anthropogenic factors made the soil heavy metal concentrations increase, especially in the center of the city. Combined with the PCA results, it was found that vehicle exhaust and smelters were the main sources of soil heavy metals. Pedogenic factors were also controlling the spatial features of metals. Discussion. Combined with the results of PCA, 7 heavy metals could be divided into 4 factors. F1 was the metals, i.e., Cu, Pb, Zn, mainly controlled by the human activities. Cr and Ni was in F2, Cd in F3 and As in F4. These 3 factors might be controlled by the soil parent materials. Concentrations of 7 heavy metals were comparable with the first level of environmental quality standard for soils of China and much lower than the second level of national standard for soils. Conclusion. The heavy metal concentrations in the topsoil of Beijing are mostly comparable with the background values, especially for As, Cr and Ni. In the city center-of Beijing, Cu, Pb and Zn had a high concentration of distribution. The spatial features of As; Cr and Ni are mainly controlled by pedogenic factors, whereas Cd, Cu, Pb and Zn are controlled by anthropogenic and parent factors. Traffic and smelting contribute greatly to the increase of Pb, Zn and Cu in the soil, especially in the center of the city. Landfill may have also affected the soil quality around it. Recommendation. Different factors were controlled by parent materials, which might be related to the different soil minerals. Further research should be conducted in Beijing to elucidate the relationship between heavy metals and soil minerals.