## 3 Results and Discussion
### Source and Pollution Degree of Heavy Metals in Soil  
#### 3.3.1 Relationships between Environmental Factors and Heavy Metals  
Statistical analysis showed that there were significant correlations among the contents of heavy metals (Table 3). The content of Pb was negatively correlated with that of As and positively correlated with that of Zn. The content Pb had no significant correlations with that of Cu, Ni, and Cr. As has a negative correlation with Zn, and a positive correlation with Cr. The Pearson correlation coefficients for Zn-Ni and Ni-Cr were close to 0.5, and the correlation was significant. The relationship between soil heavy metals and soil physicochemical properties is the result of the interaction between soil solid matter and various elements under certain environmental conditions. The pH value of the soil samples  
Figure 3: Spatial distribution layer of comprehensive pollution evaluation of soil heavy metals. in the study area varied from 3.48 to 7.06 (Table 1, Figure 4). The overall pH is weakly acidic. The contents of Pb and As were negatively correlated with pH. Reduction of soil pH usually leads to an increase in the availability of heavy metals in the soil, which is consistent with previous studies [19]. The complexation reaction (e.g., Cu(NH\({}_{3}\))\({}_{4}^{2+}\) of Cu and Zn may reduce the availability of Cu and Zn in soil. Thus, their availability is correlated with the status of ammonium nitrogen. The content of Pb was positively correlated with that of AP. Studies have shown [20] that the application of phosphorus fertilizers may also promote the accumulation of heavy metals in agricultural soils. There is a positive correlation between Pb and EC. Soil EC reflects the concentration of solutes in soil water and can affect the migration of heavy metals. Higher EC values are usually accompanied by higher metal release capacity [21]. Cr was positively correlated with CEC, indicating that the content of Cr decreased with the increase of CEC, because with the increase of CEC, the negative surface charge in the soil gradually increased, thus providing more adsorption sites to fix heavy metal ions. Soil water content and volume mass are closely related to soil texture, which is one of the important factors affecting content of soil heavy metals. Therefore, soil water content and volume mass indirectly affect the content of heavy metals [22]. There was a positive correlation between Pb and soil water content. Highly effective heavy metals pose a greater risk of migration and pose a greater threat to the surrounding environment and human health [23; 24]. Pearson correlation analysis can reveal the relationship between the two pollutants. In order to further explore the influence of various physical and chemical factors on heavy metals, CCA analysis was carried out on soil physical and chemical properties (Figure 5). NH\({}_{4}^{+}\)-N, NO\({}_{3}^{-}\)-N, AP, EC, and SWC were the main factors that affect the content of Pb. As  
Figure 4: Soil pH map. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Index** & **Pb** & **As** & **Cu** & **Zn** & **Ni** & **Cr** & **NH\({}_{4}\)-N** & **NO\({}_{3}^{-}\)-N** & **AP** & **AK** & **EC** & **CEC** & **SWC** & **pH** \\ \hline Pb & 1 & \(-0.321\)* & 0.151 & 0.310 * & \(-0.027\) & 0.135 & 0.332* & 0.317* & 0.350 ** & 0.075 & 0.251 * & 0.095 & 0.266* & \(-0.106\) \\ As & 1 & \(-0.146\) & \(-0.300\)* & \(-0.039\) & 0.275* & 0.115 & \(-0.373\)** & 0.131 & 0.158 & \(-0.015\) & \(-0.199\) & \(-0.032\) & \(-0.044\) \\ Cu & & & 1 & 0.227 & 0.190 & 0.243 & \(-0.033\) & 0.034 & 0.026 & 0.377 ** & 0.184 & 0.201 & 0.012 & 0.161 \\ Zn & & & & 1 & 0.496* & 0.094 & 0.113 & 0.179 & 0.083 & 0.215 & \(-0.052\) & 0.105 & 0.073 & 0.246 \\ Ni & & & & 1 & 0.498* & 0.108 & \(-0.077\) & \(-0.194\) & 0.002 & \(-0.215\) & 0.080 & 0.068 & 0.306 * \\ Cr & & & & & 1 & 0.146 & \(-0.171\) & 0.021 & 0.246 & \(-0.014\) & 0.255 * & 0.027 & 0.154 \\ \hline \hline \end{tabular}
\end{table}