Spatial distribution, sources and human health risk assessment of dissolved heavy metals and metalloids in Yalong River, China

The adverse effects of metal(loid) accumulation on ecological health and human health have attracted widespread attention from the society, and the reduction of species diversity in the whole Yalong River basin due to dam construction. In this study, we investigated the distribution characteristics of metal(loid)s in the whole Yalong River basin from the point of view of metal(loid)s, identified the pollution sources, assessed the risk level, and further evaluated the risk to human health. A total of 9 heavy metals (Cr, Mn, Fe, Ni, Ag, Cd, Pb, Cu and Zn) and 1 metalloid (As) were investigated and surface water samples were collected from 17 sites along the Yalong River, which were categorized into industrial and agricultural production zones (YL1–5), alpine canyon zones (YL6–12), and alpine meadow zones (YL13–17) based on altitude and habitat. The results indicated that the density of metal(loid) in the alpine meadow area was considerably highest compared to other areas. The Zn content ranged from 64.42 to 84.55 μg/L, the Mn concentration ranged from 7.47 to 20.03 μg/L, and the Pb value ranged from 0.63 to 3.44 μg/L. In other places, the concentrations for Zn ranged from 17.88 to 37.78 μg/L, for Mn they ranged from 2.84 to 12.86 μg/L, and for Pb they ranged from 0.16 to 0.50 μg/L. The main sources of the metal(loid)s were determined by correlation analysis (CA) and principal component analysis (PCA) to be from natural factors such as crustal movement, atmospheric deposition, and water-rock washout. The water quality of Yalong River was evaluated by HEI, NI and WQI indices, and the results showed that the overall water quality of Yalong River was "excellent", in which the water quality of the alpine meadow area was better than that of the industrial and agricultural production area and the alpine canyon area. HQ dermal, HQ ingestion and HI values are calculated to expose the harm caused by metal(loid) elements. The results indicate that all of the aforementioned values are below 1, suggesting that the potential harm caused by these elements is minimal. The value of HQ dermal tends to be higher than HQ ingestion. Consequently, skin contact is likely the primary mechanism of exposure. This study provides a reference basis for metal(loid) detection and ecological changes caused by the dam construction process, and provides an important basis for the use and protection of surface water in the Yalong River.