GEOCHEMICAL MOBILIZATION OF ARSENIC TO GROUND WATER Sara Baldvins CHEM 4101 December 9, 2011

Greatest Mass Poisoning in History  Naturally occurring arsenic (As) contamination in ground water is causing widespread health problems.  35 million in Bangladesh and 6 million in Bengal are at risk.  As poisoning has also been reported in China, Argentina, Chile, Mexico, Thailand, and Taiwan.

Analytical Problem Hypothesis  The speciation of arsenic in soils impacts how mobile the arsenic is which contributes to the high concentrations found in the ground water of some regions. Problem Summary  Certain soils easily mobilize As to the ground water.  In these soils certain hydrological, geological, and chemical conditions make arsenic more mobile.

Species Separation Methods TechniqueAdvantagesDisadvantages Sequential Extraction Low matrix interference, high yields, can be automated, inexpensive Time consuming, potentially large user error CEHigh resolution, great separations, quick run- times Significant matrix interference (50% recovery), low reproducibility without considerable efforts, small sample size Ion Chrom.Recovery better than 92% for most species, good resolution, reliable Loses resolution in presence of other anions, multiple interferences between the As compounds.

Sample Prep: Sequential Extraction Once the soil is ground to the appropriate particle size the reagents will be applied stepwise as follows: StepTarget Geologic Phase MgIonically bond As PO 4 Strongly adsorbed As HCl As co-precipitated w/A(V)S, oxides, and very amorphous Fe oxyhydroxides Ox As co-precipitated w/amorphous Fe oxyhydroxides HNO 3 As co-precipitated w/pyrite and amorphous As 2 S 3 Hot HNO 3 Orpiment and remaining recalcitrant As minerals

Analytical Techniques TechniqueAdvantagesDisadvantages HG-AASLeast expensive, LODs good with HG, most commonly used for As detection One species at a time, slow run time, large amount of sample preparation HG-AFSGreat LOD with HG, inexpensive Some species hard to detect, large matrix interferences ICP-MSGood LOD, multiple species at one time, short running time, less sample preparation required Requires standards, expensive, hard to run large amount of extraction sample through

Hydride Generator The are large interferences when using AAS to detect As so a Hydride Generator must be used. Schematic retrieved from

Atomic Absorption Spectrometer For the GBC 906AA w/HG:  Precision ≤ 2% for As  LOD ≤ 0.1 ppb  LOQ approx. 1 ppb  99% - 107% recovery of spiked samples

AAS Data Validated with XAS  Samples remain in solid state which eliminates the potential error from an extraction.  X-ray diffraction is used determining the arrangement of atoms in minerals and metals 200  m As XRD Map of soil sample OTT73 Toner, B. M., Nicholas, S. L., Briscoe, L. J., Knaeble, A. R., Berg, J. A., and Erickson, M. L., in press. Natural sources of arsenic to Minnesota groundwater. CURA Reporter.

X-ray Absorption Near-Edge Structure  Determines elements present in bulk or minute quantities.  Determines the formal valence, coordination complex, and oxidation state, and spin state of the probed element.  Use for quantification is not yet well defined. As3 As5 spot0 spot1 spot2 As XANES Spectra of OTT73 Toner, B. M., Nicholas, S. L., Briscoe, L. J., Knaeble, A. R., Berg, J. A., and Erickson, M. L., in press. Natural sources of arsenic to Minnesota groundwater. CURA Reporter.

Conclusions  Environmental samples are messy. Extractions can pull off a number of species other than the analyte which makes advanced technical separations difficult.  HG-AAS is cheap, effective, and a good method for bulk analysis of samples.  XANES adds validity to the HG-AAS findings by providing an exact picture of the structures in the sample without the ambiguity of an extraction.  GIS software can help give a holistic picture of the environmental system by compiling all geological, hydrological, and chemical conditions.

References 1. Anawar, Hossain M., et al. "Investigation of Sequential Chemical Extraction of Arsenic from Sediments: Variations in Sample Treatment and Extractant." Soil & Sediment Contamination 19.2 (2010): B’Hymer, C., and J. A. Caruso. "Arsenic and its Speciation Analysis using High-Performance Liquid Chromatography and Inductively Coupled Plasma Mass Spectrometry." Journal of Chromatography A (2004): Bernhard, Michalke. "Element Speciation Definitions, Analytical Methodology, and some Examples." Ecotoxicology and environmental safety 56.1 (2003): Caruso, Joseph A., and Maria Montes-Bayon. "Elemental Speciation studies—new Directions for Trace Metal Analysis." Ecotoxicology and environmental safety 56.1 (2003): Farzana Akter, Kazi, et al. "Speciation of Arsenic in Ground Water Samples: A Comparative Study of CE-UV, HG-AAS and LC- ICP-MS." Talanta 68.2 (2005): Khalid H. Al-Assaf, Julian F. Tyson, and Peter C. Uden. "Determination of Four Arsenic Species in Soil by Sequential Extraction and High Performance Liquid Chromatography with Post-Column Hydride Generation and Inductively Coupled Plasma Optical Emission Spectrometry detectionThis Article is Part of a Themed.." JAAS (Journal of Analytical Atomic Spectrometry) 24.4 (2009): Kozak, Lidia, Przemysław Niedzielski, and Witold Szczuciński. "The Methodology and Results of Determination of Inorganic Arsenic Species in Mobile Fractions of Tsunami Deposits by a Hyphenated Technique of HPLC-HG-AAS." International journal of environmental analytical chemistry (2008): Mihaljevič, M., et al. "A Comparison of Sequential Extraction Techniques for Determining Arsenic Fractionation in Synthetic Mineral Mixtures." Analytical & Bioanalytical Chemistry (2003): Niazi, Nabeel K., Balwant Singh, and Pushan Shah. "Arsenic Speciation and Phytoavailability in Contaminated Soils using a Sequential Extraction Procedure and XANES Spectroscopy." Environmental science & technology (2011): Ricci, G. R., et al. "Ion Chromatography with Atomic Absorption Spectrometric Detection for Determination of Organic and Inorganic Arsenic Species." Analytical Chemistry 53.4 (1981): Toner, B. M., Nicholas, S. L., Briscoe, L. J., Knaeble, A. R., Berg, J. A., and Erickson, M. L., in press. Natural sources of arsenic to Minnesota groundwater. CURA Reporter.