Soil heavy metal contamination assessment in the Hun-Taizi River watershed, China

Abstract

The Hun-Taizi River watershed includes the main part of the Liaoning central urban agglomeration, which contains six cities with an 80-year industrial history. A total of 272 samples were collected from different land use areas within the study area to estimate the concentration levels, spatial distributions and potential sources of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn) with a geographic information system (GIS), principal component analysis (PCA) and canonical correspondence analysis (CCA). Only the concentration of Cd was over the national standard value (GB 15618-2018). However, the heavy metal concentrations at 24.54%, 71.43%, 63.37%, 85.71, 70.33%, 53.11%, and 72.16% of the sampling points were higher than the local soil background values for As, Cd, Cr, Cu, Hg, Ni, Pb and Zn, respectively, which were used as standard values in this study. The maximal values of Cd (16.61 times higher than the background value) and Hg (12.18 times higher than the background value) had high concentrations, while Cd was present in the study area at higher values than in some other basins in China. Cd was the primary pollutant in the study area due to its concentration and potential ecological risk contribution. The results of the potential ecological risk index (RI) calculation showed that the overall heavy metal pollution level of the soil was considerably high. Three groups of heavy metals with similar distributions and sources were identified through PCA. The results of the CCA showed that the distribution of mines was the strongest factor affecting the distributions of Ni, As, Zn, Pb, and Cd. However, Cu was strongly influenced by the distance to the nearest river. These findings can provide scientific support for critical planning and strategies for soil pollution control and removal to support the sustainable development of the study area.

Figure 1

Location of the study area.

Figure 2

Spatial distribution of eight heavy metals in the study area.

Figure 3

Spatial distribution of the potential ecological risk index (a) and classification (b).

Figure 4

Loadings of the first components obtained from PCA.

Figure 5

Maps of effect factors.

Figure 6

Canonical correspondence analysis between eight heavy metal concentrations and effect factors. Abbreviations: D2STP – Distance to sewage treatment plants, D2Re – Distance to reservoirs, D2City – Distance to cities, D2Mi – Distance to mines, D2MPF – Distance to main pollution factories, D2Vi – Distance to villages, D2Ro – Distance to roads, D2Ri – Distance to rivers.