Arsenic associations in sediments from shallow aquifers of northwestern Hetao Basin,Inner Mongolia |
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Authors: | Yamin Deng Yanxin Wang Teng Ma Hui Yang Jun He |
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Institution: | (1) Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan, Hubei, 430074, People’s Republic of China;(2) US Geological Survey, Boulder, CO 80302, USA;(3) Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA;(4) Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin, Guangxi, 541004, China;(5) Wuhan Center of Geological Survey, China Geological Survey, Wuhan, Hubei, 430205, China; |
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Abstract: | Understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management
in areas of endemic arsenic poisoning, such as the Hetao Basin in Inner Mongolia, northern China. Aquifer geochemistry was
characterized at three field sites (SH, HF, TYS) in Hangjinhouqi County of northwestern Hetao Basin. The results of bulk geochemistry
analysis of sediment samples indicated that total As concentrations have a range of 6.8–58.5 mg/kg, with a median of 14.4 mg/kg.
The highest As concentrations were found at 15–25 m depth. In the meanwhile, the range of As concentration in the sediments
from background borehole is 3–21.8 mg/kg, with a median value of 9 mg/kg. The As sediments concentrations with depth from
the SH borehole were correlated with the contents of Fe, Sb, B, V, total C and total S. Generally, the abundance of elements
varied with grain size, with higher concentrations in finer fractions of the sediments. Distinct lithology profile and different
geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse
sedimentary environments. Up to one third of arsenic in the sediments could be extracted by ammonium oxalate, suggesting that
Fe oxyhydroxides may be the major sink of As in the aquifer. Sequential extraction results indicate that arsenic occurs as
strongly adsorbed on and/or co-precipitated with amorphous Fe oxyhydroxides in sediments accounting for 35 and 20%, respectively,
of the total contents of arsenic. The release of As into groundwater may occur by desorption from the mineral surface driven
by reductive dissolution of the Fe oxide minerals. Furthermore, small proportions of As associated with iron sulfides occur
in the reductive sediments. |
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