Hydrochemical composition, distribution, and sources of typical organic pollutants and metals in Lake Bangong Co, Tibet

Lake Bangong Co is a special lake in western Tibet, with characteristics of increased salinity from the eastern area to the western area. Due to its remote location and poor environmental conditions, there are few background data on the water environment of this lake. In this study, the water chemical composition of Lake Bangong Co was studied, and the concentration levels, distribution characteristics, and pollution sources of polycyclic aromatic hydrocarbons (PAHs), phthalic acid esters (PAEs), and metals (As, Pb, Cr, Mn, Cu, Cd, Ni, and Zn) were investigated. The hydrochemical characteristics of the lake showed significant spatial differences. Conductivity, salinity, degree of mineralization, total hardness, Cl⁻, and SO₄²⁻ generally increased from the eastern part to the western part. Most water quality parameters met the class III standards of the Chinese surface water standards; however, the Cl⁻ and SO₄²⁻ concentrations in the western part exceeded the surface water standard limits. ΣPAH and ΣPAE concentrations in lake water have no significant relationship with hydrochemical parameters. Among the 16 target PAHs, 4 PAH monomers with a (5 + 6)-ring were not detected in the lake water. The main sources of PAHs included emissions from biomass combustion, petroleum volatilization, and automobile exhaust. Six PAE monomers were detected at all sampling sites with relatively low concentrations, and di-2-ethylhexyl phthalate (DEHP) and di-n-butyl phthalate (DBP) were the main pollutants. The main source of PAEs was domestic waste, which might be related to increasing human activities in this area recently. In general, the concentrations of metals in the water of Lake Bangong Co were lower than those in the regions affected by anthropogenic activities except As. The results of PCA showed that As, Cu, and Cr mainly originated from natural sources; Pb, Mn, and Cr came from both natural and anthropogenic sources; and Cd was highly likely from anthropogenic sources.