UK Dust Network – 2nd Workshop Claire Horwell 14 th March 2008

1. UK Dust Network – 2nd WorkshopClaire Horwell14th March 2008 Mineralogy & Volcanology

2. Objectives of field: • To use mineralogy and geochemistry to make rapid assessments of the potential health hazard of natural mineral particles. • To understand WHY a mineral or dust may trigger a pathogenic respiratory response.

3. 15 µm Sources: • Volcanoes • Volcanic ash • Aerosols (liquid & solid) • Dust storms • Sourced from: • Glacial forelands • Debris fans • Deserts • Exposed lake beds • Biogenic dust • bacteria, pollen, diatoms (silica) • Quarrying and mining of rock Beijing, China, 2003 Phytolith (bacterium)

4. 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?

5. Horwell, 2007, JEM Malvern Mastersizer 2000 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

6. Horwell, 2007, JEM Grain size - volcanoes

7. Composition of heterogeneous dusts • Volcanic ash and 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 and cristobalite. • Raman-SEM allows polymorphic determination of individual crystals/particles. SEM image of volcanic ash

8. Reactivity of surfaces • Electron Spin Resonance detects free and surface radicals. • Radicals formed by breaking bonds during fragmentation • Radicals are highly reactive, damaging DNA, proteins, lipids etc. • Likely to be one of several triggering mechanisms for chronic lung disease.

9. Production of silica surface radicals • Soufrière Hills dome-collapse ash shows no generation of silica radicals (peaks expected at point A). • Distinctive curve and peak (at point B) shows interaction of iron. • Crystalline silica alone (Talvitie residue) has less iron but no significant generation of silica radicals. Horwell et al. Environmental Research, 2003

10. Production of hydroxyl radicals:Fenton Reaction: Fe2+ + H2O2 Fe3+ + OH- + HO Horwell et al. Environmental Research, 2003

11. Production of hydroxyl radicals Basaltic Andesitic/ Dacitic Tephritic/ Phonolitic Horwell, Fenoglio & Fubini, in review Minusil 5 Quartz standard

12. Purity of crystalline silica • One could say that if a dust is respirable and contains x-silica then it is a potential health hazard. • BUT toxicological and epidemiological evidence appears to suggest that volcanic silica isn’t 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 for high resolution micro-analysis e.g. TEM-EDX, FIB thinning etc.

13. How pure is volcanic x-silica? • 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. SEM-EDX spectrum of cristobalite 1 mm

14. Results – dome rock • In dome rock we see euhedral and platey crystals which have grown in cracks and vesicles by vapour-phase deposition. • Raman-SEM confirms these are cristobalite. Cristobalite in dome rock vugh Raman spectra from cristobalite in dome rock 1 mm Horwell, Williamson & Le Blond, in prep.

15. Cristobalite composition – dome rock • Electron microprobe shows that the cristobalite is compositionally distinct from volcanic quartz, containing impurities of Al and Na. platey cris. euhedral cris. quartz 1 mm Horwell, Williamson & Le Blond (in prep.)

16. SEM-EDX Elemental maps Case Study 1 – Volcanic ashEarly results • In thin section, cracked appearance. • Devitrification of glass also produces crystalline silica. Blue = Si Pink = K Green = Al 1 mm

17. SEM-EDX Elemental maps Case Study 1 – Volcanic ashEarly results • In thin section, cracked appearance. • Devitrification of glass also produces crystalline silica. • Would not fragment as microlites. Blue = Si Pink = K Green = Al 1 mm ?

18. Where do we go from here? • Could alpha and beta forms of cristobalite and 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 and desert. • Horwell NERC Fellowship. 1 mm

19. A useful tool for predicting the respirable fraction: Data collected by Malvern Mastersizer 2000 laser diffractometer. n = 65 samples from volcanoes worldwide.