Measurement of labile arsenic speciation in water and soil using diffusive gradients in thin films (DGT) and X-ray absorption near edge spectroscopy (XANES)

Environmental context Both inorganic and organic arsenic species are toxic to the environment when labile. The Diffusive Gradients in Thin Films technique, equipped with ferrihydrite binding gel enables measurement of labile arsenic species from water and soil solutions. This study indicated that labile arsenic species are quantitatively adsorbed to the gel, and that they are stable for up to 2 weeks following deployment. Abstract Arsenic speciation was determined in the solution extracted from a ferrihydrite binding gel layer in a DGT unit (FB-DGT) deployed in water using coupled high-performance liquid chromatography and hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS). However, the extent of change in arsenic speciation during the extraction process is unknown. By identifying the arsenic species in the FB-DGT gel directly, using X-ray absorption near edge spectroscopy (XANES) fitting with model arsenic compounds, we obtain a better understanding of the ability of FB-DGT to measure labile arsenic species in solution. The results presented herein confirm that FB-DGT accumulated labile inorganic and methylated arsenic species. Arsenic species bound to the FB-DGT gel were stable for up to 2 weeks following deployment. However, caution should be applied when interpreting the proportion of As species measured by HPLC-HG-AFS in solution extracted from FB-DGT because the distribution of arsenic species in extracted solutions was found to be modified by the extraction process. Some (~20%) of arsenate was converted into arsenite, and a significant amount (~25%) of dimethylarsinic acid (DMAsV) was converted into monomethylarsonic acid (MMAsV) or arsenate (AsV). Only inorganic arsenite (iAsIII) was stable during the extraction process. These findings suggested that, based on the XANES measurement, although As species were quantitatively accumulated in the FB-DGT gel, the FB-DGT technique was still unsuitable for studying As speciation. This is because changes in arsenic speciation were observed to occur during gel extraction, prior to HPLC-HG-AFS measurement, and because the XANES technique is available for routine measurements.

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Speciation and Lability of Ag-, AgCl-, and Ag2S-Nanoparticles in Soil Determined by X-ray Absorption Spectroscopy and Diffusive Gradients in Thin Films

Environmental Science & Technology ◽

10.1021/es504229h ◽

2014 ◽

Vol 49 (2) ◽

pp. 897-905 ◽

Cited By ~ 66

Author(s):

R. Sekine ◽

G. Brunetti ◽

E. Donner ◽

M. Khaksar ◽

K. Vasilev ◽

...

Keyword(s):

Thin Films ◽

Absorption Spectroscopy ◽

X Ray ◽

Ag2s Nanoparticles ◽

Diffusive Gradients ◽

X Ray Absorption

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Contribution of organic arsenic species to total arsenic measurements using ferrihydrite-backed diffusive gradients in thin films (DGT)

Environmental Chemistry ◽

10.1071/en11057 ◽

2012 ◽

Vol 9 (1) ◽

pp. 55 ◽

Cited By ~ 12

Author(s):

Heléne Österlund ◽

Mikko Faarinen ◽

Johan Ingri ◽

Douglas C. Baxter

Keyword(s):

Thin Films ◽

Natural Waters ◽

Arsenic Speciation ◽

Inorganic Arsenic ◽

Speciation Analysis ◽

Arsenic Species ◽

Future Studies ◽

Organic Arsenic ◽

Arsenic Determination ◽

Diffusive Gradients

Environmental contextBoth the mobility and toxicity of arsenic in natural waters are related to the aqueous species distribution. Passive sampling using ferrihydrite-backed diffusive gradients in thin films (DGT) devices has in previous studies been characterised to measure labile inorganic arsenic, and the possible contribution of organic species has been disregarded. This study shows that the two most prevalent organic arsenic species might be included in DGT measurements, which should be taken into consideration when evaluating DGT data in future studies. AbstractIn previous publications discussing arsenic determination using ferrihydrite-backed diffusive gradients in thin films (DGT) devices, organic arsenic forms have been disregarded, even though it is known that the two most prevalent in natural waters, dimethylarsinate (DMA) and monomethylarsonate (MMA), may adsorb to ferrihydrite and thereby be included in the measurement. In this work the accumulation of DMA and MMA, as well as inorganic arsenite and arsenate, to ferrihydrite-backed DGT devices was investigated. It could be demonstrated that MMA, and under acidic conditions also DMA, adsorbed to the binding layer and might therefore contribute to the total mass of measured arsenic. Diffusion coefficients were measured for all four species to enable quantification of DGT-labile concentrations of organic and inorganic arsenic. Elution of the analytes from the ferrihydrite binding layer was performed using 1 mL of 1 M NaOH to facilitate arsenic speciation analysis using chromatographic separation. Average recovery rates were between 87 and 108 %. This study shows that the contribution of DMA and MMA to the total accumulated mass must be taken into consideration when evaluating DGT data in future studies.

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An XPS and XANES Study on the Bioleaching of Arsenopyrite with or without Pyrite

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.262.53 ◽

2017 ◽

Vol 262 ◽

pp. 53-56 ◽

Cited By ~ 2

Author(s):

Yi Yang ◽

Wei Hua Liu ◽

Chun Wang ◽

Miao Chen ◽

Rahul Ram ◽

...

Keyword(s):

Photoelectron Spectroscopy ◽

Arsenic Speciation ◽

Arsenic Species ◽

Leaching Rate ◽

X Ray Diffraction ◽

Edge Structure ◽

Chemical Leaching ◽

X Ray ◽

Moderate Thermophiles ◽

X Ray Absorption

In the present study, we investigated the bioleaching of arsenopyrite with or without pyrite by moderate thermophiles. In both chemical leaching and bioleaching, the addition of pyrite decreased the leaching rate of arsenopyrite. The arsenic speciation and minerology changes in the residues were analysed by X-ray Absorption Near Edge Structure (XANES) Spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and powder X-ray Diffraction (XRD). The XANES analysis showed no detectable arsenopyrite in the final residues from the experiments without pyrite. However, there was still 21.7% of arsenic species presented as arsenopyrite after bioleaching, when the initial arsenopyrite/pyrite ratio was 1:5. The XPS analysis revealed there was only As(V) on the surface of most of the residues, except on one chemically leached sample where As(III) was found.

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