Abstract: Kuitun River Basin in Xinjiang is the first endemic arsenic poisoned area in mainland China. The causes of excessive arsenic in the groundwater in Kuitun River Basin have not been clarified due to human activities and natural conditions. In the present research, we analyzed the main and trace element components in 51 groups of surface water and groundwater samples collected in 2017, as well as the particle size and chemical composition of 44 groups of sediment samples from two boreholes in typical high arsenic content area in 2019. Results unveiled that the concentration of arsenic in groundwater of Kuitun River Basin ranged from 10-887 μg/L, averaging 55.8 μg/L, and in sediment reaching 28.41 mg/kg to the maximum, which exceeded the standard (10 μg/L) largely. Siderite, calcium arsenate, manganese arsenate and other minerals distributed in the surrounding mountainous areas provided material sources for the excessive arsenic concentration in groundwater; strong evaporation and rock weathering further aggravated the arsenic concentration in groundwater; high pH and low Eh values of groundwater caused arsenate to desorb from the mineral surface and accumulate in groundwater. The reduction process of Fe/Mn oxide minerals in sediments and clay minerals released the coexisting arsenic, which is also the reason why arsenic in groundwater exceeded standard.

Key words: groundwater, arsenic, pH value, reducing environment, sediment, Kuitun River