In Vitro Bioaccessibility of Arsenic in Arsenopyrite

Contamination from legacy sulfide mine tailings is a persistent problem due to elevated concentrations of toxic metal(loid)s, e.g., arsenic. In semi-arid regions, such as the Southwestern US, dry climate and lack of vegetative cover create conditions for off-site transport of tailings as fugitive dusts. This poses a considerable risk to proximal communities who can experience exposure through incidental inhalation and ingestion of particulate matter. Generally, arsenopyrite (FeAsS) is the parent rock mineral for arsenic at many sulfide ore derived mine tailings sites. Initial in vitro bioaccessibility (IVBA) experiments – conducted under anoxic conditions, with rigorous cleaning of oxidized surficial precipitates, and utilizing HPLC-ICP-MS for aqueous speciation analyses – suggested that arsenopyrite reacted in synthetic gastric fluid to release arsenate (AsV) to solution. The apparent oxidation of As during FeAsS dissolution was unexpected, and could reflect the co-elution of thioarsenicals with pentavalent arsenate in HPLC-ICP-MS. Thus, a new set of experiments were conducted using synthetic thioarsenical standards, testing their stability in the development of new HPLC-ESI-MS/MS and HPLC-ICP-MS methods. Relevance of this work is supported by the fact that there is little known about the aqueous stability of thioarsenical compounds during FeAsS dissolution, despite their high toxicity