UK Dust Network – 1 st Workshop Claire Horwell 24th May 2007

1. UK Dust Network – 1st WorkshopClaire Horwell24th May 2007 Cutting edge techniques for the analysis of volcanic ash and other natural particles

2. Objectives: • To use mineralogy and geochemistry to make rapid assessments of the potential health hazard of volcanic ash (and other natural dusts). • To understand WHY a mineral or dust may trigger a pathogenic respiratory response.

3. Questions to be answered: • Is the dust small enough to enter the lungs? • What is the composition of the dust? • Is the surface of the dust reactive? • Are individual particles ‘pure’? • Other ideas?

4. Horwell, 2007, accepted for publication Malvern Mastersizer 2000 Grain size • Is the dust small enough to enter the lungs? • Grain size analysis techniques: • Laser diffraction • 70 analyses from around the world • SEM with image analysis • Sieving • > 63 mm only • New predictive technique

5. Composition of heterogeneous dusts • Volcanic ash is 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

6. 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.

7. 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

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

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

10. Purity of crystalline silica • One could say that if the ash 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.

11. 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 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

12. Early 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.

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

14. 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

15. 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 ?

16. Where do we go from here? • Could alpha and beta forms of cristobalite and quartz have different toxicities? • Extremely unusual to preserve beta variety but impurities potentially make it possible. • Integration of work with toxicology. • Application of techniques to other natural dusts e.g. coal and desert. 1 mm

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