Hydrochemical processes controlling arsenic and selenium in the Changjiang River (Yangtze River) system

The hydrochemistry of arsenic and selenium in the Changjiang (Yangtze River) was studied, based on continuously monitored data at Nantong station (i.e. 180 km inland from river mouth), the main Changjiang channel and 10 major tributaries. The dissolved inorganic arsenic (DIAs) and selenium (DISe) concentrations of the Changjiang are related to water discharge, rock type of drain basin, anthropogenic influences etc. The DIAs and DISe levels vary over an order of magnitude throughout the basin (i.e. 6.95–68.9 nmol/L for DIAs, 1.16–9.92 nmol/L for DISe). Source rock composition is the primary control on the concentrations of DIAs and DISe in the Changjiang. Several tributaries (e.g. Xiangjiang River, Minjiang River and Tuojiang River) are contaminated by human activities. Flux calculations from hydrographic data at Datong (the most downstream main channel station without tidal influence) indicate that the Changjiang transports 234.8 × 105 mol/yr of DIAs and 49.6 × 105 mol/yr of DISe to the East China Sea.