Distribution of groundwater arsenic in Xinjiang, P.R. China

•Spatial distribution of groundwater As was investigated in Xinjiang.•High As groundwater was found in the north, south and east of Xinjiang.•Arsenic concentrations generally increased with the increase in well depths.•Desorption and/or reductive dissolution led to As enrichment in groundwater.•Model-based prediction of groundwater As would deviate from real data.

Although potential contamination of groundwater As is expected to occur in Xinjiang, P.R. China, few data are available for the regional distribution of groundwater As. In this study, the spatial distribution of groundwater As was investigated in the Chepaizi (CPZ-N) and Shihezi (SHZ-N) areas of northern Xinjiang, the Balikun-Yiwu Basin (BY-E) in eastern Xinjiang, and the Tarim (TRM-S) and Yanqi (YQ-S) basins in southern Xinjiang. Arsenic concentrations greater than 10 μg/L were found in 12% of analyzed groundwaters. All groundwater samples collected in CPZ-N had As concentrations greater than 10 μg/L (25-185 μg/L), 30% in SHZ-N (<0.25-49 μg/L), 2.7% in BY-E, and 6.1% in TRM-S and YQ-S. No high As groundwater (As >10 μg/L) was found in the eastern and southern TRM-S and YQ-S. Distribution of groundwater As showed a tremendous spatial variability, which greatly varied over a short distance horizontally. Arsenic concentration generally increased with increasing sampling depth. The spatial distribution of groundwater As would be regulated by As source and hydrogeochemical processes. Higher pH and/or lower ORP values were generally observed in high As groundwater (>10 μg/L) in comparison with low As groundwater (<10 μg/L). Arsenic mobility in SHZ-N and CPZ-N may result from As desorption under relatively high pH conditions, and more tentatively from reductive dissolution of Fe(III) oxides in BY-E and TRM-S. However, detailed mechanisms of As mobilization in these regions need further investigation.