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TitleSpeciation of micrometer-sized particles using synchrotron X-ray fluorescence, absorption and microdiffraction
AuthorJamieson, H; Lanzirotti, A; Corriveau, M; Parsons, M
SourceEos, Transactions of the American Geophysical Union vol. 90, no. 22, Suppl., Abstract MA21B-05, 2009.
Alt SeriesEarth Sciences Sector, Contribution Series 20080740
PublisherAmerican Geophysical Union
MeetingAmerican Geophysical Union 2009 Joint Assembly; Toronto, ON; CA; May 24-27, 2009
Mediaon-line; digital
Subjectsgeochemistry; Health and Safety; analytical methods; x-ray fluorescence; x-ray diffraction; absorption; arsenic; gold; mines; scorodite; arsenates; yukonite; human health
ProgramEnvironment and Health
AbstractSynchrotron-based X-ray microprobe analysis is well-suited to the characterization of aerosol particles chemically and mineralogically. It can provide quantitative information about major and trace element abundances with femtogram detection sensitivity by x-ray fluorescence. Multi-element mapping provides mass ratios for selected elements on thousands of particles, which can be used to infer mineralogy based on composition. Information on elemental speciation can be obtained utilizing x-ray absorption spectroscopy, and microbeam x-ray diffraction on selected particles can be used to unambiguously identify microcrystalline materials. For aerosol analysis particulate filters can be analysed directly with no additional preparation. Samples were collected in seven aerodynamically fractionated size ranges using a cascade impactor deployed at three abandoned gold mine tailings fields in Nova Scotia. Analysis was conducted at beamline X26A at the National Synchrotron Light Source. This study's focus was on As-bearing particles since our previous work had identified high concentrations of As in unconsolidated near-surface materials, including various weathering products of arsenopyrite. Results from the 1-2, 4-8 and 8-16 micrometer size fractions indicate a strong correlation between As and Fe, particularly in the smaller size fractions. There are no As-bearing particles that do not contain Fe and few Fe-bearing particles that do not contain As. Calculated As/Fe ratios suggest the particles are mostly scorodite (FeAsO4.2H2O) and hydrous Fe arsenate, consistent with our mineralogical studies of coarser near-surface material. The presence of nanocrystalline scorodite is confirmed by X-ray microdiffraction of selected As-rich particles. Microdiffraction also indicates the presence of amorphous As-Fe phases. MicroXANES analysis of selected As-rich particles on the filters indicates that most contain As(V), also consistent with mineralogical observations on near-surface tailings samples. Yukonite and other Ca-Fe arsenates are unlikely based on the lack of correlation between Ca and As. This is significant since our previous work has shown that yukonite-bearing samples are associated with higher gastric bioaccessibility than scorodite-rich samples. Windblown and vehicle-raised dust from the unvegetated portions of these mine tailings sites, some of which are publicly accessible and used for recreational activities, may be ingested or inhaled. Results from this study can be used to help assess the potential human health risks associated with exposure to As-bearing airborne particles.