UK Dust Network 2nd Workshop Claire Horwell 14th March 2008 Mineralogy & Volca
Long-Garcia, John, Managing Editor has reference to this Academic Journal, PHwiki organized this Journal UK Dust Network 2nd Workshop Claire Horwell 14th March 2008 Mineralogy & Volcanology Objectives of field: To use mineralogy in addition to geochemistry to make rapid assessments of the potential health hazard of natural mineral particles. To underst in addition to WHY a mineral or dust may trigger a pathogenic respiratory response. Sources: Volcanoes Volcanic ash Aerosols (liquid & solid) Dust storms Sourced from: Glacial as long as el in addition to s Debris fans Deserts Exposed lake beds Biogenic dust bacteria, pollen, diatoms (silica) Quarrying in addition to mining of rock Phytolith (bacterium) Beijing, China, 2003
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Questions to be answered: Is the dust small enough to enter the lungs What is the composition of the dust Is shape a relevant factor (e.g. fibrous) Is the surface of the dust reactive Are individual particles pure Is the crystalline structure of the mineral relevant Grain size Is the dust small enough to enter the lungs Grain size analysis techniques: Laser diffraction SEM with image analysis Sieving > 63 mm only New predictive technique Horwell, 2007, JEM Grain size – volcanoes Horwell, 2007, JEM
Composition of heterogeneous dusts SEM image of volcanic ash Volcanic ash in addition to eroded dusts are often composed of tens of minerals. Some are considered toxic e.g. crystalline silica. Analytical techniques: SEM-EDX gives individual particle compositions but not polymorphs. XRD-PSD gives quantity of minerals in a bulk sample. High res. so no overlap between plagioclase in addition to cristobalite. Raman-SEM allows polymorphic determination of individual crystals/particles. Reactivity of surfaces Electron Spin Resonance detects free in addition to surface radicals. Radicals as long as med by breaking bonds during fragmentation Radicals are highly reactive, damaging DNA, proteins, lipids etc. Likely to be one of several triggering mechanisms as long as chronic lung disease. Production of silica surface radicals Horwell et al. Environmental Research, 2003 Soufrière Hills dome-collapse ash shows no generation of silica radicals (peaks expected at point A). Distinctive curve in addition to peak (at point B) shows interaction of iron. Crystalline silica alone (Talvitie residue) has less iron but no significant generation of silica radicals.
Production of hydroxyl radicals: Fenton Reaction: Fe2+ + H2O2 Fe3+ + OH- + HO Horwell et al. Environmental Research, 2003 Production of hydroxyl radicals Basaltic Andesitic/ Dacitic Tephritic/ Phonolitic Minusil 5 Quartz st in addition to ard Horwell, Fenoglio & Fubini, in review Purity of crystalline silica One could say that if a dust is respirable in addition to contains x-silica then it is a potential health hazard. BUT toxicological in addition to epidemiological evidence appears to suggest that volcanic silica isnt very toxic. We can use mineralogy to determine WHY x-silica is/ is not toxic. The problem: Difficult to analyse differences in composition at the nano-scale. Timeliness: New technology as long as high resolution micro-analysis e.g. TEM-EDX, FIB thinning etc.
How pure is volcanic x-silica SEM-EDX spectrum of cristobalite 1 mm Crystalline silica in volcanic ash may be modified by more-inert components. E.g. it is known that Al ameliorates silica toxicity. Evidence: SEM-EDX work indicates that silica particles are impure. The silica particles may be modified by: occlusion by glass intergrowth with glass or plagioclase substitution of Si from atomic structure by Al & Na. Results dome rock Cristobalite in dome rock vugh 1 mm In dome rock we see euhedral in addition to platey crystals which have grown in cracks in addition to vesicles by vapour-phase deposition. Raman-SEM confirms these are cristobalite. Horwell, Williamson & Le Blond, in prep. Raman spectra from cristobalite in dome rock Cristobalite composition dome rock 1 mm Electron microprobe shows that the cristobalite is compositionally distinct from volcanic quartz, containing impurities of Al in addition to Na. Horwell, Williamson & Le Blond (in prep.) quartz euhedral cris. platey cris.
Case Study 1 Volcanic ash Early results 1 mm SEM-EDX Elemental maps In thin section, cracked appearance. Devitrification of glass also produces crystalline silica. Blue = Si Pink = K Green = Al Case Study 1 Volcanic ash Early results 1 mm SEM-EDX Elemental maps In thin section, cracked appearance. Devitrification of glass also produces crystalline silica. Would not fragment as microlites. Blue = Si Pink = K Green = Al Where do we go from here 1 mm Could alpha in addition to beta as long as ms of cristobalite in addition to quartz have different toxicities Leverhulme proposal: Horwell, Williamson, Donaldson, Cressey (Fubini, Carpenter, Parman) Integration of work with toxicology. Leverhulme proposal Michnowicz PhD (April 2008) Application of techniques to other natural dusts e.g. coal in addition to desert. Horwell NERC Fellowship.
A useful tool as long as predicting the respirable fraction: Data collected by Malvern Mastersizer 2000 laser diffractometer. n = 65 samples from volcanoes worldwide.
Long-Garcia, John Managing Editor
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