Bioavailabilty, Release Kinetics, and Molecular Speciation of Arsenic and Lead in Geo-dusts from the Iron King Mine Federal Superfund Site in Humboldt, Arizona
Arizona has approximately 60,000-100,000 abandoned or inactive mining sites. Mine tailing disposal sites in arid areas such as Arizona are susceptible to wind erosion and become sources of airborne particulate matter or geo-dusts including <10 μm (PM10 & PM2.5). These particulate matter are comprised of metal(loid) contaminants such as arsenic, lead, mercury and cadmium and are listed in the ATSDR’s Priority List of Hazardous Substances as they are detrimental to human health. Additionally, climate models predict that Southwestern U.S. will become increasingly warmer and drier increasing the harmful effects of these airborne metal(loid) contaminants.
This research aims to use surface samples from Iron King Mine to i) identify the particle size impact on bioaccessibility ii) determine the relative bioaccessibility of arsenic in simulated lung and gastric fluids and iii) determine the molecular speciation via analysis of the post-extraction sample solid using synchrotron-based X-ray absorption spectroscopy (XAFS and XANES) and x-ray diffraction (XRD). All extraction solutions were analyzed for total solubilized arsenic and lead via acid-digestion and ICP-MS.
Mine tailing surface samples were collected and sieved to obtain size fractions relevant to ingestion (<150 μm) and inhalation (<10 μm). These size fractions were then extracted with simulated gastric and lung fluids to determine the bioaccessibility of arsenic and lead. Kinetic studies included short (30 second time steps) to long (7 day) time steps to determine the rate of reaction progression and impact of particulate matter residence time on bioaccessibility. We hypothesize that (i) smaller particles with greater surface area will have accelerated kinetics of arsenic and lead release, and (ii) bioaccessibility is a predictable function of the local contaminant bonding environment (i.e. arsenic and iron bonds) as revealed from spectroscopy. This research is important to environmental human health risk assessment and to increasing the accuracy of exposure to toxic metal(loid)s from ingested and inhaled mine tailing geo-dusts.