## 3 Results
### Pollution Indices  
The evaluated results of pollution indices listed in Table 1 are illustrated in Figure 2 for city parks, landfill, and industrial area. The results of the Geoaccumulation index and \(I_{MN}\) revealed that more than 70% of the measured 132 samples collected from city parks were moderately and moderately to highly polluted by heavy metals (Figure 2a). Samples showing slight or high to serious heavy metal pollution were about 10% of the total 132 samples. According to the results of the Geoaccumulation index for each heavy metal element illustrated in Figure 2a, almost all samples were unpolluted or slightly polluted by Ni and Cr. Most samples were slightly or moderately polluted by Cu, Zn, Pb, and As. However, most soil samples collected from city parks were moderately, moderately to highly, highly, seriously, or even extremely seriously polluted by Cd and Hg. Therefore, it can be concluded that the main pollution elements in urban city park soils in Guangzhou were Cd and Hg. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Area** & **Cu** & **Zn** & **Ni** & **Pb** & **Cr** & **As** & **Cd** & **Hg** \\ \hline \multirow{4}{*}{City parks} & Min & 8.2 & 18.0 & 6.4 & 22.2 & 13.0 & 6.3 & 0.012 & 0.006 \\  & Max & 240.0 & 3660.0 & 65.1 & 564.0 & 145.0 & 305.0 & 15.800 & 11.950 \\  & Ave & 44.0 & 203.0 & 19.9 & 105.0 & 51.7 & 34.7 & 0.599 & 0.804 \\  & Std. & 32.0 & 351.7 & 9.2 & 77.1 & 18.1 & 35.7 & 1.502 & 1.329 \\  & CV (\%) & 73.0 & 173.2 & 46.4 & 73.4 & 35.0 & 103.2 & 251.8 & 165.4 \\ \hline \multirow{4}{*}{Landfill} & Min & 8.3 & 13.0 & 4.8 & 14.8 & 12.0 & 5.3 & 0.010 & 0.006 \\  & Max & 160.0 & 268.0 & 127.5 & 5420.0 & 145.0 & 604.0 & 3.150 & 0.217 \\  & Ave & 24.4 & 83.2 & 19.3 & 177.7 & 44.6 & 56.4 & 0.310 & 0.105 \\  & Std. & 28.2 & 55.4 & 22.8 & 839.6 & 27.6 & 109.2 & 0.515 & 0.059 \\  & CV (\%) & 115.6 & 66.6 & 118.4 & 472.5 & 61.9 & 193.8 & 165.8 & 59.2 \\ \hline \multirow{4}{*}{Industrial area} & Min & 9.6 & 56.0 & 8.0 & 46.0 & 21.0 & 5.1 & 0.101 & 0.043 \\  & Max & 2365.0 & 5640.0 & 136.8 & 942.0 & 1120.0 & 78.5 & 17.650 & 1.570 \\  & Ave & 170.4 & 601.1 & 30.8 & 204.6 & 107.0 & 19.3 & 1.415 & 0.353 \\  & Std. & 407.2 & 1080.6 & 28.9 & 200.4 & 162.2 & 14.0 & 2.452 & 0.312 \\  & CV (\%) & 239.0 & 179.8 & 93.7 & 97.9 & 151.6 & 72.5 & 173.3 & 88.5 \\ \hline \multicolumn{8}{c}{Background value of surface soil (A horizon) in Guangzhou *} & 17.0 & 47.3 & 14.4 & 36.0 & 50.5 & 8.9 & 0.056 & 0.078 \\ \hline \hline \end{tabular}  
* Data taken from The Background Values of Soil Elements in China [88].  
\end{table} 
Table 3: Statistical summary of heavy metal contents (unit: mg/kg). Figure 2: _Cont._  
As for soil samples collected from the vicinity of the landfill, 73.2% of all samples were moderately to seriously polluted by heavy metals. All samples were clean or were slightly polluted by heavy metals Cr and Hg. More than ninety percent of the measured samples were unpolluted or slightly polluted by heavy metals Cu, Zn, Ni, and Pb. However, 56.1% and 48.8% of the measured samples collected from the vicinity of the landfill were moderately, moderately to highly, highly, and seriously polluted by Cd and As, respectively (Figure 2b). As for the calculated results of I\({}_{\text{MN}}\) for soil samples collected from the industrial area, nearly 90% samples were moderately to seriously polluted by heavy metals. Furthermore, some samples collected from the industrial area were even extremely seriously polluted by HMs (Figure 2c). Fortunately, most surface soil samples collected from the industrial area showed no or only slight pollution by Ni (85.7%), Cr (87.5%), and As (69.6%). Of the measured soil samples collected from the industrial area, 32.1%, 35.7%, and 44.6% were unpolluted or slightly polluted by heavy metals Cu, Pb, and Hg. For all measured soil samples from the industrial area, percentages of moderate Cu, Pb, and Hg pollution were 46.4%, 37.5%, and 30.4%, respectively.