The fate, transport, and toxicity of harmful elements in mine wastes are often considerably enhanced in the finest-grained particle size fractions. For example, the natural presence of arsenic (a known carcinogen) and other trace elements in gold deposits has led to an environmental legacy of arsenic contamination in abandoned gold mine tailings (processed ore) throughout the western United States, where fine-grained arsenic-bearing particles are transported by both windborne and waterborne processes from tailings piles to surrounding background regions. This poses substantial environmental risks because of the documented enrichment of arsenic with decreasing particle size and the increased exposure pathways of fine-grained particles, particularly those that can be ingested (≤250 m), respired (≤10 m), and delivered deep into the lung cavity (≤2.5 m).

Fundamental links between the geochemical and physical properties of airborne dust particles and the bioaccessibility* and bioavailability** of potentially harmful elements in these particles have not yet been clearly established, preventing a basic understanding of the relationships between dust composition, chemical speciation and particle toxicity, thus impairing risk assessment efforts in mining-impacted regions. We have collected the ≤10 µm size fraction of (processed) mine tailings and (unprocessed) waste rock, measured a series of geochemical and physical parameters, conducted benchtop simulated inhalation exposures to measure arsenic bioaccessibility, and finally conducted live rat exposure studies with both samples to track arsenic bioavailability in a living organism.

Intellectual merit: From our initial findings we can conclude: 1) arsenic is released in the urine in two stages: a rapid release representing the mobilization of a soluble As phase within the first 5 days post-exposure followed by a slower release of a less-soluble As phase after 5 days; 2) arsenic can be detected immediately in the lungs and blood post-exposure, with exponential declines in arsenic concentration with time out to 7 days; 3) arsenic displays complex behavior in the kidney, heart, and liver over time with general declines out to 7 days; and 4) exposure to the respirable mine tailings generally results in elevated arsenic levels compared to the respirable waste rock.

Broader impacts: This work has involved the training of 3 current undergraduate students and 6 recent graduates in basic lab skills, field sampling methodology, size separation analysis, in vitro extraction experiments, in vivo exposure studies, tissue digestion and dilution, and data analysis. Many of these students are continuing their studies as Ph.D. students in the sciences, research positions in industry, or medical school.  Additionally, results have been presented at national scientific meetings, campus research days, and high school talks, increasing the dissemination of our findings to a broader audience. Finally, while our studies largely address basic research questions relevant to the field of low-temperature environmental geochemistry, they have significant implications for those working in the fields of environmental remediation, environmental health and safety, and environmental toxicology.  The identification of arsenic species and their relative concentration, bioaccessibility, and mobility in airborne mine tailings particulates is important for those charged with the development of applied remediation strategies in mining-impacted lands.  

*proportion of an inhaled element released from solid particles into a biologically-relevant medium, e.g. lung fluid

**proportion of the inhaled element that is released from solid particles and retained or incorporated into the body 

Last Modified: 01/10/2017
Modified by: Christopher S Kim