## 3 Results and Discussion  
### Concentration of PTEs in Soils of the Study Area  
Table 3 shows the descriptive statistics of the analyzed PTE concentrations and pH values of the collected surface soils from the Baoshan area, as well as local, regional, national, and relevant reference guideline values. The pH values of the surface soils from the research area ranged from 4.13 to 8.33 (median: 6.46; mean: 6.45). The registered median values for the concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were 16, 0.19, 113, 41, 0.10, 51, 34, and 100 mg/kg, respectively. All PTEs were above their national background values. The registered median values for the concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were 1.78, 1.73, 2.26, 2.16, 5.56, 2.32, 1.62, and 1.67 times higher than their corresponding national background values, respectively [87]. With the exception of Pb, all of the studied PTEs were above their regional background values (background values of Yunnan province) [88]. In particular, the median values of the Cd, Hg, and Cr concentrations were 2.29, 2.00, and 1.66 times higher than their corresponding regional  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Exposure Way** & **R\({}_{\text{f}}\)D\({}_{\text{ingestion}}\)** & **R\({}_{\text{f}}\)D\({}_{\text{inhalation}}\)** & **R\({}_{\text{f}}\)D\({}_{\text{dermal}}\)** & **SF\({}_{\text{ingestion}}\)** & **SF\({}_{\text{inhalation}}\)** & **SF\({}_{\text{dermal}}\)** & **References** \\ \hline As & 0.0003 & 0.000301 & 0.000123 & 1.5 & 15 & 3.66 & [85] \\ Cd & 0.001 & 0.001 & 0.00001 & - & 6.3 & - & [85] \\ Cr & 0.003 & 0.0000286 & 0.00006 & 0.5 & 42 & - & [85] \\ Cu & 0.04 & 0.0402 & 0.012 & - & - & - & [85] \\ Hg & 0.0003 & 0.000024 & 0.0003 & - & - & - & [85] \\ Ni & 0.02 & 0.0201 & 0.0054 & - & 0.84 & - & [85] \\ Pb & 0.0035 & 0.00352 & 0.000525 & - & 0.0042 & - & [74] \\ Zn & 0.3 & 0.3 & 0.06 & - & - & - & [85] \\ \hline \end{tabular} Note: “-” not available.  
\end{table}
Table 2: The reference dose and slope factor for each PTE and exposure way.  
background values, respectively. However, no noticeable enrichments (>1.5 times) or deficits (<0.8 times) were identified when compared to the local background values of the studied PTEs [54]. When the PTE contents in the surface soil from the Baoshan area were compared to those found in the Australian surface soil [89], the American soil A layer [90], and the surface soil of the European continent [91] (Table 3), the contents of the PTEs in the surface soil of the study area were about 1.5 times higher or more than those in the surface soil of the American, Australian, and European continents. This fact indicates that the study area is a typical geological background area with high PTE levels, and the elevated PTE concentrations in the surface soil are mainly due to geological genesis [54]. The PTE contents in the surface soil of the study area are similar to those in the Sacramento Valley of Northern California, USA [60]. This area is similar to the Baoshan area, which is widely characterized with ultra-basic rocks and mineral deposits (such as As, Hg, Zn, Cu, Au, and Ag) [60]. The concentrations of As, Cd, Cu, Hg, Pb, and Zn in the surface soil collected from the study area were significantly lower than those found in the soil around the mining areas in other research studies [5; 92] and in the surface soils deposited in areas with carbonate rocks as the main parent material [93]. Meanwhile, the Cr, Ni, and Cu concentrations in the present study area were determined to be significantly lower when compared to those in the surface soil in areas where ultra-basic rocks are the main parent materials [94].