Heavy metals in suspended particulate matter in the Yarlung Tsangpo River, Southwest China

Analyzing suspended particulate matter (SPM) in rivers has become crucial to assessing heavy metals in the fluvial system due to SPM's outstanding transportability. The Tibetan Plateau (TP), especially the Yarlung Tsangpo River (YTR) area, is under the potential threat of heavy metal pollution. Ten selected heavy metal elements (V, Cr, Co, Ni, Cu, Zn, As, Cd, Sb and Cs) were assessed in 27 SPM samples collected from the YTR main channel and its tributaries in June and September 2017 for the enrichment, temporal-spatial variation and potential source analysis of heavy metals in the YTR. The seasonal mean concentrations of the detected heavy metal followed the trend: Zn (290) > Cu (171) > As (144) > V (121) > Cr (91.5) > Ni (85.3) > Cs (74.3) > Co (28.1) > Sb (4.39) > Cd (0.57). The enrichment factor (EF) values suggested Cu (6.54), As (5.68), and Cd (4.45) as the most enriched heavy metal elements in the YTR, referring to moderate to severe enrichment, while other heavy metals were condonable. Temporally, heavy metals were more enriched in the SPM samples collected in September than in June because of the discrepancy in hydrodynamic conditions. Spatially, hot-spring-related elements showed a declining tendency downstream of the YTR. In the middle of the YTR, those heavy metals sensitive to anthropogenic activities would significantly concentrate in the SPM because it is the most populated and developed area in Tibet. Additionally, tributaries would accumulate more heavy metals than the YTR mainstream. Principal component analysis (PCA) extracted five components for heavy metals in the SPM. It revealed that hot springs and multivariate human activities would be the dominant contributors to the concentrated heavy metals in the SPM of the YTR.