## 4 Discussion
### Source Analysis of Heavy Metal(loid) Pollution  
Accurate identification of pollution sources is vital for the prevention and control of soil heavy metal(loid) pollution [38; 39]. Pearson and principal component analyses were used to broadly classify the sources of the eight heavy metal(loid)s contaminating construction land into three categories. During the first stage (As, Cd, Hg, Pb, and Zn), the mean values of these elements significantly exceeded the soil background values in Kunming (Figure 2). The Cv values of As, Hg, Cd, Pb, and Zn were high, indicating that they were subjected to large anthropogenic factors. Industrial pollution significantly affects  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{**Item**} & \multicolumn{3}{c}{**Construction Land (A)**} & \multicolumn{3}{c}{**Agricultural Land (B)**} \\ \cline{2-7}  & \multicolumn{3}{c}{**Principal Component Factors (Maximum Variance Rotated Solution)**} \\ \cline{2-7}  & **PC1** & **PC2** & **PC3** & **PC1** & **PC2** & **PC3** \\ \hline As & 0.956 & 0.223 & 0.124 & 0.877 & 0.128 & \(-\)0.166 \\ Hg & 0.951 & 0.137 & 0.002 & 0.805 & 0.130 & 0380 \\ Cd & 0.893 & 0.324 & 0.254 & 0.798 & 0.214 & 0.323 \\ Pb & 0.869 & 0.352 & 0.159 & 0.781 & 0.038 & 0.147 \\ Ni & 0.319 & 0.920 & 0.156 & 0.155 & 0.898 & 0.222 \\ Cu & 0.739 & 0.505 & \(-\)0.050 & \(-\)0.020 & 0.533 & 0.756 \\ Cr & 0.125 & 0.104 & 0.974 & 0.157 & 0.884 & \(-\)0.128 \\ Zn & 0.813 & 0.332 & 0.325 & 0.338 & \(-\)0.166 & 0.729 \\ eigenvalue & 4.696 & 1.519 & 1.185 & 2.827 & 1.980 & 1.467 \\ variance (\%) & 58.596 & 18.985 & 14.813 & 35.340 & 24.752 & 18.336 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Principal component analysis results of soil heavy metal(loid) elements in construction land and agricultural land.  
Figure 5: Spatial distribution of principal components of heavy metal(loid)s in soil of construction land (**A**) and agricultural land (**B**).  
As and Hg are greatly affected by industrial pollution [40; 41]. There are more vehicles in industrial parks, and these enterprises include automobile recycling and dismantling. Cd and Pb may originate from automobile exhaust emissions and tire wear, whereas Pb and Zn may originate from engine wear, braking, or other sources [42]. Metal smelting is the primary cause of Cd and Pb pollution [43; 44].  
The second category (Ni and Cu) includes elements that occur in metal smelting wastes [45; 46]. The third category comprises only Cr and is strongly influenced by motor vehicle exhaust [47], although Cr is released in varying degrees from various parts of the cement production process [48].  
The eight heavy metal(loid)s in the agricultural land were divided into three categories. In the first stage (As, Hg, Cd, and Pb), the average values of the four elements were higher than the background values of the soil in Kunming. The spatial variability of Hg, Cd, and Pb was more obvious. Irrational use of fertilizers and pesticides has led to increased concentrations of As, Cd, and Pb in soil [49; 50; 51]. Hg contamination is caused by industrial and agricultural pollutants (the latter involves the long-term use of chemical pesticides) [52; 53]. Cd can reflect a high Cd geological background and transportation source [54; 55].  
The second category (Ni and Cr) is less affected by anthropogenic factors. Ni and Cr are closely related to soil matrix formation [56; 57]. The third category comprises Cu and Zn, which originate from chicken and pig manure applied during cultivation. Fertilizers containing P or other chemicals can also produce Zn when applied [58].