期刊
ENVIRONMENTAL SCIENCE & TECHNOLOGY
卷 52, 期 2, 页码 616-627出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.7b05176
关键词
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资金
- DOE Office of Science by Argonne National Laboratory [DE-AC02-06CH11357]
- Swiss National Science Foundation [200021_138003]
X-ray amorphous Fe(III)-As(V) coprecipitates are common initial products of oxidative As- and Fe-bearing sulfide weathering, and often control As solubility in mine wastes or mining-impacted soils. The formation conditions of these solids may exert a major control on their mineralogical composition and, hence, As release in the gastric tract of humans after incidental ingestion of As-contaminated soil. Here, we synthesized a set of 35 Fe(III)-As(V) coprecipitates as a function of pH (1.5-8) and initial molar Fe/As ratio (0.8-8.0). The solids were characterized by synchrotron X-ray diffraction, FT-IR spectroscopy, and electrophoretic mobility measurements, and their As bioaccessibility (BA(As)) was evaluated using the gastric-phase Solubility/Bioavailability Research Consortium in vitro assay (SBRC-G). The coprecipitates contained 1.01-4.51 mol kg(-1) As (molar Fe/As-solid: 1.00-8.29) and comprised varying proportions of X-ray amorphous hydrous ferric arsenates (HFA(am)) and As(V)-adsorbed ferrihydrite. HFA(am) was detected up to pH 6 and its fraction decreased with increasing pH and molar Fe/As ratio. Bioaccessible As ranged from 2.9 to 7.3% of total As ((x) over bar = 4.8%). The BA(As) of coprecipitates formed at pH = 4 was highest at formation pH 3 and <= 4 and controlled by the intrinsically high solubility of the HFA(am) component, possibly enhanced by sorbed sulfate. In contrast, the BAAs of coprecipitates dominated by As(V)-adsorbed ferrihydrite was much lower and controlled by As readsorption and/or surface precipitation in the gastric fluid. Bioaccessible As increased up to 95% with increasing liquid-to-solid ratio, indicating an enhanced solubility of these solids due to interactions between Fe and the glycine buffer. We conclude (i) that natural Fe(III)-As(V) coprecipitates exhibit a particularly high solubility in the human gastric tract when formed at pH similar to 3-4 in the presence of sulfate, and (ii) that the in vitro bioaccessibility of As in Fe(III)-As(V) coprecipitates as assessed by tbe SBRC-G assay depends critically on their solid-phase concentration in As-contaminated soil and mine-waste materials.
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