Identifying the origins and spatial distributions of heavy metals in soils of Ju country (Eastern China) using multivariate and geostatistical approach

Abstract

Identifying the sources of heavy metals in soils is a crucial issue for soil remediation and management. Most regions in China have been undergoing a rapid industrialization and urbanization since the last three decades. However, there is little information available on the spatial distribution of heavy metals in soils experiencing a rapid transition from agricultural-based to industrial-based economy. To resolve this problem and to provide references on similar regions, we carried out an investigation on heavy metals in soils in Ju country to identify potential sources and to map their spatial distributions. A total of 646 samples including 511 samples in topsoils (0–20 cm, regular grid of 2 × 2 km2) and 135 samples in subsoils (150–200 cm, regular grid of 4 × 4 km2) were collected in Ju country, and the total contents of Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, and Zn were determined. Enrichment factor method and multivariate analyses (correlation analysis, principal component analysis, and cluster analysis) were applied to identify the sources of ten heavy metals in topsoils. Additionally, ordinary kriging was used to map the spatial distributions of heavy metals concentration in topsoils. The overall levels of all heavy metals did not show high values, but the enrichment factor results suggested that Hg, Cd, Cu, Pb, and Zn in topsoils showed significant accumulation. Ten heavy metals can be grouped into three groups. Co, Cr, Mn, Ni, and V were associated with parent material and seemed to originate from a natural source. Cd, Cu, Pb, and Zn seemed to be related to the combination of parent material and anthropic inputs. Hg as an isolated element was dominated by atmospheric deposition inputs related to various human activities. Distribution maps derived by ordinary kriging suggested that Cd, Cu, Hg, Pb, and Zn were linked to the western part, corresponding well to the surroundings of urban areas located in the western part of Ju country. Hg, Cd, Cu, Pb, and Zn were the main metals affected by human inputs in Ju country, and the high risk resulting from human influence was mainly shown around urban areas, consistent with the spatial distribution of industrial and traffic sites. Agricultural practices did not have significant influence on the spatial distribution of metals. The combination of multivariate analysis and geostatistics was found to be an effective approach to identify the origins and spatial distribution of heavy metals in soils.