*3.5. Cluster Analysis*

Cluster Analysis (CA) is a method used to group data according to their similarity [19]. Hierarchical Cluster Analysis (HCA) was applied based on the Wards method and Euclidean distance methods [9]. The HCA result (Figure 3) indicated that elements were clustered into two major clusters. The first cluster includes Cr, Fe, Cu, Ni, Co and Hg. The second cluster includes As, Cd, Zn, Pb and Sb. HCA indicated that there is a close cluster between Cr and Fe, Ni and Cu, Co and Hg, As and Cd and Zn and Pb. This implied that those elements were from the same sources. Pearson's correlation analysis also pointed out that those elements had a strong positive correlation which suggested that the elements have the same common origin. The moderate cluster between elements (Figure 3) indicated that these elements share similar sources.

### *3.6. Contamination Level and Ecological Risk of Trace Elements*

Contamination factor, degree of contamination, ecological risk factor, potential ecological risk index and enrichment factor and the geo-accumulation index of trace elements were evaluated and the results presented in Table 7.

**Table 7.** Contamination Factor (*Cif*), Degree of Contamination (*Cd*), Ecological Risk Factor (*Eif*), Risk Index (*RI*), Enrichment Factor (*EF*) and Geo-accumulation Index (*Igeo*) of trace elements.


The obtained result of (*Cif*) indicated that Co > Cd > Ni > Pb > Cu > Cr > As > Hg > Fe > Sb > Zn. According to the obtained value of (*Cif*), the contamination level of trace elements are grouped

as low contamination from Zn (0.03), Fe (0.93) and Sb (0.35), moderate contamination from Cr, Ni, Cu, As, Hg and Pb and a high contamination of soil from Co and Cd. The degree of contamination (*Cd*) for elements for this the study was 1560.2, which indicates a high degree of soil contamination. Ecological risk factors (*Eif*) for single elements were in the decreasing order of Co > Cd > Hg > Ni > Pb > As > Cu > Sb > Cr > Zn > Fe. According to the classification given for ecological risk factor for single elements in Table 1, Cr, Ni, Cu, As, Zn, Pb, Fe and Sb had low-risk factors, Hg had a moderate risk factor and Cd and Co had an extremely high risk factors. Thus, Cd, Hg and Co can cause high risk to human and environment in Huangpi district. The same result was reported on Cd and Hg from East Dongting and Honghu Lake in Hunan Province, China [37]. The potential risk index (*RI*) for this study was 5352.03, which indicated a high ecological risk due to these trace elements. The obtained enrichment factor of elements revealed that soil is enriched with Co and Cd, moderately enriched with Ni, Cu, Hg and Pb; and less enriched with Cr, Fe As and Sb (Table 7). This indicated that there is a high rate of anthropogenic disturbance in Huangpi soil. Extremely high enrichment for Cd was also reported by [72] and [73]. The obtained *Igeo* values of the elements in soil were in decreasing order of Co > Cd > Ni >Cu > Pb > Cr > As > Hg > Fe > Sb > Zn. According to the seven classes proposed by [45], the obtained *Igeo* result revealed that the soils under study were extremely contaminated with Cd and Co, moderately contaminated with Cr, Ni, Cu and Pb and less contaminated with As, Zn, Hg, Fe and Sb. The obtained *Igeo* result for Cd was in line with those of [72,74,75].
