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A gel probe equilibrium sampler for measuring arsenic porewater profiles and sorption gradients in sediments: II. Field application to Haiwee reservoir sediment

Environmental Science and Technology

By:
, , , and
DOI: 10.1021/es071120a

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Abstract

Arsenic (As) geochemistry and sorption behavior were measured in As- and iron (Fe)-rich sediments of Haiwee Reservoir by deploying undoped (clear) polyacrylamide gels and hydrous ferric oxide (HFO)-doped gels in a gel probe equilibrium sampler, which is a novel technique for directly measuring the effects of porewater composition on As adsorption to Fe oxides phases in situ. Arsenic is deposited at the sediment surface as As(V) and is reduced to As(III) in the upper layers of the sediment (0-8 cm), but the reduction of As(V) does not cause mobilization into the porewater. Dissolved As and Fe concentrations increased at depth in the sediment column driven by the reductive dissolution of amorphous Fe(III) oxyhydroxides and conversion to a mixed Fe(II, III) green rust-type phase. Adsorption of As and phosphorous (P) onto HFO-doped gels was inhibited at intermediate depths (10-20 cm), possibly due to dissolved organic or inorganic carbon, indicating that dissolved As concentrations were at least partially controlled by porewater composition rather than surface site availability. In sediments that had been recently exposed to air, the region of sorption inhibition was not observed, suggesting that prior exposure to air affected the extent of reductive dissolution, porewater chemistry, and As adsorption behavior. Arsenic adsorption onto the HFO-doped gels increased at depths >20 cm, and the extent of adsorption was most likely controlled by the competitive effects of dissolved phosphate. Sediment As adsorption capacity appeared to be controlled by changes in porewater composition and competitive effects at shallower depths, and by reductive dissolution and availability of sorption sites at greater burial depths. ?? 2008 American Chemical Society.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A gel probe equilibrium sampler for measuring arsenic porewater profiles and sorption gradients in sediments: II. Field application to Haiwee reservoir sediment
Series title:
Environmental Science and Technology
DOI:
10.1021/es071120a
Volume
42
Issue:
2
Year Published:
2008
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Environmental Science and Technology
First page:
504
Last page:
510