# Analysis of Heavy Metal Sources in Xutuan Mining Area Based on APCS-MLR and PMF Model
## 3 Results and Discussion
### Morphological Distribution Characteristics of Heavy Metals in Sediments  
Heavy metals extracted by acid solutions are easily susceptible to changes in external environments, resulting in their release from sediments into water bodies, thus affecting water environments. Therefore, different forms of sediment heavy metals can be used to assess associated short-term ecological risks. As can be seen from Figure 3, F5 was the most important form of Cu, accounting for an average proportion of 49.39%, followed by F4 (20.55%), F3 (12.83%), F1 (10.39%), and F2 (6.84%), respectively. Similarly, F5 was the most dominant Cr form (65.78%), followed by F4 (28.33%) and F3 (4.78%) as well as by F1 and F2, which accounted for 1.11%. The main form of Zn was F5 (52.56%), followed, by F4 (30.5%), F2 (7.94%), F3 (6.61%), and F1 (2.39%), respectively. As was also dominated by the F5 form, with a relative proportion of 50.94%, followed by F4 (30.67%), F3 (11.06%), F2 (6.72%), and F1 (0.61%), respectively. In contrast, F4 was the most dominant form of Cd, accounting for 27.89%, followed by F5 (24.89%), F3 (18.5%), F2 (16.06%), and F1 (12.66%), respectively. A similar finding was observed for Pb, showing a comparatively higher proportion of the F4 form (53.39%), followed by F5 (20.94%), F1 (10.61%), F3 (9.89%), and F2 (5.17%), respectively. The F5 form of Cu, Cr, and Zn has a weak release capacity, derived mainly from natural sources due to the lower contents of these heavy metal elements than the corresponding background values of Xutuan City. The higher F4 proportion of Pb might be due to the strong adsorption ability of sediment organic matter to Pb. The content of organic matter in the bottom mud of the mining area is relatively rich (5.14-10.05%), and heavy metal elements easily combine with organic functional groups, humic acids, and small molecular compounds generated by the decomposition of organic matter to form relatively stable compounds. The adsorption capacity of these compounds are much higher than that of other colloids in the sediment. The non-F5 proportions of Cd and Pb were 75.11 and 79.06%, respectively. Studies have shown that there is a strong relationship between the content of heavy metals in sediments and pH value. When the sediment is acidic, the content of heavy metals in the sediment is reduced due to desorption, but when the pH value is 7, the desorption of heavy metals is effectively inhibited. However, when the pH value is >8, the heavy metal content reaches the maximum adsorption capacity and no longer increases with the increase in pH value [35]. The average pH of the sediment in the mining area is 7.09, which can effectively inhibit the desorption of heavy metals. Nevertheless, Cd-related environmental issues cannot be ignored due to the high content and strong toxicity of this heavy metal element. On the other hand, the non-F5 contents of Pb were lower than the corresponding background value of Xutuan soil. The release of the different heavy metal forms into the environment can be enhanced by increasing their proportions and contents of heavy metals, causing sediment and water pollution and consequently increasing their biological availability. The F5 form, on the other hand, can be released mainly through weathering processes, as it is often attached to mineral materials, reducing the likelihood of secondary environmental pollution [36]. Although As exhibited higher contents in the sediments than the national soil level II standard, its F5 form accounted for a relatively high proportion, indicating a low likelihood of associated environmental pollution in the study area.