## 4 Discussion  
### Spatial Distribution Characteristics of HMs in Sediments  
River sediments act as both sources and sinks of water pollution, with a significant accumulation of pollutants in contaminated rivers [57; 58; 59]. The average concentrations of various HMs in the sediments of the YR are presented in Table S3. The average concentrations of Cr, Ni, Cu, and Pb are lower than the average background values of HMs in Chinese river sediments, while the average concentrations of Zn, As, and Cd exceed the average background values of HMs in Chinese river sediments. Higher concentrations of Cr, Ni, Cu, and Zn in sediments are observed in the sections of Qinghai and Ningxia, which may be attributed to local mineral resource exploitation and economic development. For example, the high rate of HM pollution in the Huangshui River in the economically developed Xining section has been reported [60], and pollution in the Ningxia section may also be due to the discharge of agricultural and industrial wastewater [61]. The higher concentration of Zn in the Inner Mongolia section is a result of the development of the steel manufacturing and rare earth mining industries, which has led to an increase in  
Figure 7: Assessment of non-carcinogenic and carcinogenic risks posed by HMs in sediments. (**a**) Non-carcinogenic Risk in Adult Males. (**b**) Non-carcinogenic Risk in Adult Females. (**c**) Non-carcinogenic Risk in Children. (**d**) Carcinogenic Risk in Adult Males. (**e**) Carcinogenic Risk in Adult Females. (**f**) Carcinogenic Risk in Children. the concentration of Zn in sediments [62]. In addition, high levels of HMs are observed from Sanmenxia City to Zhengzhou City, which is due to the extensive gold mining and agricultural activities in Lingbao City, located near Sanmenxia City [63]. In this study, PMF was used to identify the sources of HMs, and the results indicated that traffic-industrial sources, agricultural-industrial sources, and industrial sources are potential contributors of HMs in the sediments, with contribution rates of 32.47%, 44.87%, and 22.66%, respectively. Previous studies have shown that the extensive use of fertilizers and pesticides in agricultural production leads to the entry of HM elements from these chemicals into rivers through rainwater runoff, thereby increasing the HM content in water bodies [64; 65]. Phosphate rock and potash fertilizers often contain HM impurities, and HM components in pesticides may also enter the soil and water bodies during application [66; 67]. Industrial emissions are one of the main sources of HM pollution in river sediments. Wastewater and slag emissions from high-energy-consuming and highly polluting industries, such as chemical, steel, and nonferrous metals, contain a large number of HM elements [51; 52]. Transportation is also an important source of HM pollution in river sediments [68]. HM elements in the fuel and coatings used during ship navigation may be discharged into rivers through exhaust gases, wastewater, and solid waste. The results of this study show that the HMs Pb, Cu, and Zn in the sediments originate from a mixed source of traffic and industry; As, Cr, Ni, and Cd originate from a mixed source of agriculture and industry; and Cd originates from agriculture (Figure 6). Therefore, source control should be the primary strategy for HM pollution control in sediments, fundamentally reducing the potential threats of HMs to river ecosystems and human health. In addition, different strategies should be developed for different pollution sources to form a comprehensive and systematic governance situation. The dynamics of HMs in the YRB are influenced by both natural and anthropogenic factors [12; 69]. Hydrological conditions, such as river flow and sediment transport, affect the distribution and deposition of HMs [70]. During the flood season, the resuspension and transport of sediments increase, which may lead to the redistribution of HMs within the basin [71; 72].