Investigations towards a better understanding of arsenic-sulfur speciation in aquatic environments: Formation, stability, structural characterization, and conflicting analyses
type: CreativeWork
description: Arsenic is a widespread contaminant of global concerns due to its neurotoxicity and carcinogenicity. Particularly critical is the speciation of arsenic, influencing its mobility, toxicity and retention capability. Recently, it was analytically proven that arsenic-sulfur (As-S) species play a dominant role for arsenic cycling in sulfidic systems. The geochemistry of As-S species is not well investigated, yet, and especially the nature of these species, thioarsenites vs. thioarsenates, has been under intense debate. The major objective of the present PhD work was to improve the current knowledge about As-S species by structural characterization, investigations of their occurrence, formation and transformation, and evaluation of the analytical techniques, X-ray absorption spectroscopy (XAS) and ion chromatography coupled to ICP-MS (IC-ICP-MS). By XAS it was shown that under strictly anoxic conditions thioarsenites form in arsenite-sulfide mixes with sulfide (SH-) excess and as co-occurring intermediates during acidic transformation of thioarsenates. Thioarsenites can be specified as highly labile, converting rapidly to thioarsenates in the presence of traces of oxygen, e.g. during standard IC-ICP-MS analyses. Excess hydroxide (OH-) either due to high pH or sample dilution in ultrapure water inhibits the formation of thioarsenites by SH--OH- competition. These facts make the current IC-ICP-MS method even under anoxic conditions unsuitable for thioarsenite analyses. However, thioarsenites were shown to be necessary intermediates for formation of thioarsenates. Thioarsenates determined in natural oxic systems are thus most likely the product of rapid in-situ thioarsenite oxidation. Direct thioarsenite determination is currently only possible by XAS with a limitation on > 5 mM-solutions for structural evaluations. The characteristic coordination and bond length (RAs-S 2.23-2.28 Å) makes thioarsenites distinguishable from thioarsenates (RAs-O 1.70 Å, RAs-S 2.13-2.18 Å). The…
abstract: Arsenic is a widespread contaminant of global concerns due to its neurotoxicity and carcinogenicity. Particularly critical is the speciation of arsenic, influencing its mobility, toxicity and retention capability. Recently, it was analytically proven that arsenic-sulfur (As-S) species play a dominant role for arsenic cycling in sulfidic systems. The geochemistry of As-S species is not well investigated, yet, and especially the nature of these species, thioarsenites vs. thioarsenates, has been under intense debate. The major objective of the present PhD work was to improve the current knowledge about As-S species by structural characterization, investigations of their occurrence, formation and transformation, and evaluation of the analytical techniques, X-ray absorption spectroscopy (XAS) and ion chromatography coupled to ICP-MS (IC-ICP-MS). By XAS it was shown that under strictly anoxic conditions thioarsenites form in arsenite-sulfide mixes with sulfide (SH-) excess and as co-occurring intermediates during acidic transformation of thioarsenates. Thioarsenites can be specified as highly labile, converting rapidly to thioarsenates in the presence of traces of oxygen, e.g. during standard IC-ICP-MS analyses. Excess hydroxide (OH-) either due to high pH or sample dilution in ultrapure water inhibits the formation of thioarsenites by SH--OH- competition. These facts make the current IC-ICP-MS method even under anoxic conditions unsuitable for thioarsenite analyses. However, thioarsenites were shown to be necessary intermediates for formation of thioarsenates. Thioarsenates determined in natural oxic systems are thus most likely the product of rapid in-situ thioarsenite oxidation. Direct thioarsenite determination is currently only possible by XAS with a limitation on > 5 mM-solutions for structural evaluations. The characteristic coordination and bond length (RAs-S 2.23-2.28 Å) makes thioarsenites distinguishable from thioarsenates (RAs-O 1.70 Å, RAs-S 2.13-2.18 Å). The…
author: Süß, Elke
date published: 2011-05-23
date modified: 2026-07-27T18:49:09Z
provider: Universität Bayreuth
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Universität Bayreuth