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RESEARCH ARTICLE

Synchrotron X-ray absorption spectroscopy analysis of arsenic chemical speciation in human nail clippings

Olena Ponomarenko A E , Mihai R. Gherase B , Mark S. LeBlanc B , Chang-Yong Kim C , Elstan D. Desouza D , Michael J. Farquharson D , Fiona E. McNeill D , Susan Nehzati A , Ingrid J. Pickering A , Graham N. George A and David E. B. Fleming B E
+ Author Affiliations
- Author Affiliations

A Molecular and Environmental Sciences Research Group, Department of Geological Sciences, University of Saskatchewan, SK, S7N 5E2 Canada.

B Physics Department, Mount Allison University, Sackville, NB, E4L 1E6, Canada.

C Canadian Light Source, 44 Innovation Boulevard, Saskatoon, SK, S7N 2V3, Canada.

D Department of Medical Physics and Applied Radiation Sciences, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4K1, Canada.

E Corresponding authors. Email: olena.ponomarenko@usask.ca; dfleming@mta.ca

Environmental Chemistry 11(6) 632-643 https://doi.org/10.1071/EN13240
Submitted: 24 December 2013  Accepted: 12 August 2014   Published: 16 December 2014

Environmental context. Chronic ingestion of arsenic leads to its accumulation in keratinous tissues, which can represent a risk factor for developing cancer. We use synchrotron X-ray absorption spectroscopy to investigate chemical bonding of arsenic in the keratins from nail clippings of volunteers from areas in Atlantic Canada with low-to-moderate arsenic contamination of drinking water. The study helps our understanding of arsenic metabolism and its role in cancer development.

Abstract. Drinking water aquifers in many areas of the world have naturally elevated levels of inorganic arsenic exceeding the World Health Organization limit. Arsenic concentrations in human nail clippings are commonly used as a biomarker of exposure to this toxic element. However, the chemical form of arsenic accumulated in nail tissues is not well determined. We employed synchrotron microprobe and bulk X-ray absorption spectroscopy techniques to analyse the concentration and chemical speciation of arsenic in the finger- and toenail clippings of volunteers living in the vicinity of Sackville, New Brunswick, Canada. This area is known to have low-to-moderately elevated levels of arsenic in ground water. Arsenic species in clippings were represented by three main groups, distinguished by the As-K near-edge X-ray absorption fine structure spectra: (1) AsIII type, which can be fitted as a mixture of As bound to thiols, and also to oxygen or methyl groups, with a small contribution from AsV species, (2) AsV type, best represented by fitting arsenate in aqueous solution and (3) The AsIII + AsV mixture type. The high proportion (%) of sulfur-bound arsenic species most likely corresponds to binding between arsenic (in its trivalent and, to a lesser extent, pentavalent forms) and cysteine residues in the sulfur-rich fraction of keratin and keratin-associated proteins. Further work is needed to explore whether these chemical species could be used as toxicity biomarkers of human exposure to elevated levels of As in drinking water.

Additional keywords: arsenicosis, chemical speciation, keratin, near-edge X-ray absorption fine structure, synchrotron X-ray fluorescence (XRF) imaging.


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