## 3 Results and Discussion
### Soil Heavy Metal Source Apportionment
#### 3.2.2 PMF Analysis and Source Apportionment
It can be inferred that factor 2 may represent atmospheric deposition from human emissions [55]. Approximately 38% of all Hg emissions in China come from coal combustion, 45% from non-ferrous metal smelling, and 17% from other activities. The smelling of non-ferrous metals and coal mining and combustion significantly contribute to the accumulation of Hg in soil [52; 56]. As is often found in association with Zn produced from metal smelling and commonly occurs in its sulfide form naturally in coal and metal ones. Atmospheric deposition can lead to soil contamination with As and Zn around metallurgical enterprises [53]. The high contribution rate of Hg almost certainly links factor 2 to these activities. Furthermore, Hg can be transported over long distances through the atmosphere and enters the soil via both dry and wet deposition [55]. Therefore, factor 2 is likely representative of coal combustion and atmospheric pollution sources. Factor 3 is predominantly weighted by Mn at 78.8%, with secondary contributions from Cd at 49.6%, Co at 39.9%, V at 31.6%, Cu at 27.4%, Zn at 26.5%, and Pb at 25%. Mn is a common metallic element, and numerous prior studies have indicated that the presence of Mn in soil may be controlled by the soil parent material [43; 57]. The significant contribution of factor 1, which refers to natural sources, to Mn further supports this assertion. Thus, factor 3 is characterized as a non-natural source. Mn is widely used in industry, particularly in steel production as an alloying element to enhance strength and corrosion resistance, in  
Figure 10: Factor loadings plot from the PMF model using soil heavy metal concentration data. (In the figure, (**a**) represents Factor 1, (**b**) represents Factor 2, (**c**) represents Factor 3, and (**d**) represents Factor 4). batteries such as alkaline Mn batteries, and in chemical products including pigments and catalysts. [57; 58; 59; 60; 61]. Zn, Pb, and Cu are typical contaminants associated with steel mills [62]. The secondary contributions of Cd (49.6%), Zn (26.5%), and Pb (25%) may suggest that they originate from the non-ferrous metal smelling process [63]. The accumulation of Cd is primarily attributed to increased industrial waste emissions, particularly from Pb-Zn mining and metal smelling, with severe Cd pollution in areas surrounding paper mills, which is a characteristic pollutant from the paper industry [53]. Pb, Cd, and Hg are also associated with metal casting facilities, entering the soil through atmospheric deposition of smelling fumes, leaching of industrial waste, and wastewater discharge [54]. Therefore, factor 3 is likely linked to these industrial activities. In summary, factor 3 is likely representative of industrial pollution sources from non-ferrous metal smelling and the paper industry. Factor 4 is primarily weighted by Ni at 78.3%, with secondary contributions from Cr at 55.8%, Pb at 52.5%, Cu at 47.6%, Zn at 46%, and V at 44.4%. Ni, Cr, and Pb are correlated (Figure 6), and these elements represent anthropogenic sources derived from domestic/urban wastewater and vehicle emissions [64]. Cd, Pb, and Zn are considered trace elements in traffic exhaust [65]. Ni and Pb are significant markers of traffic-related pollution, with over 80% of Ni emissions attributed to exhaust discharge. Pb is associated with the combustion of leaded gasoline and tire wear. Cu and Ni may also originate from traffic emissions, as over 90% of Cu found in traffic emissions is due to brake wear, with Cu, Zn, and Pb being the most abundant metals in brake linings [53; 66]. Meanwhile, Cr and Ni are generally regarded as the least polluting elements in urban soils in China, with Cr linked to parent rock and natural sources [50; 53; 54]. Thus, factor 4 is likely representative of traffic emission pollution sources.