Surface Properties of Particles
The analysis of the surface reactivity of volcanic ash is a new field of volcanic health hazard research being pioneered using Electron Paramagnetic Resonance (EPR) spectroscopy at the Università degli Studi di Torino, Italy.
Crystalline silica is considered to be a human carcinogen and is capable of causing silicosis, a potentially-fatal fibrotic lung disease. Volcanic ash often contains crystalline silica, present as the polymorphs quartz, cristobalite or tridymite. Recent work on the Soufriere Hills volcanic ash (Montserrat, West Indies) has shown that ash derived from dome-collapse eruptions contained substantial quantities of respirable cristobalite (Horwell et al. 2003a). Cristobalite is considered to have a greater potential to cause lung disease than the more common silica polymorph, quartz.
Much work has been carried out on the link between reactivity of the surface of mineralogical particles, such as quartz, and the biological environment as the effects of an insoluble solid in the lung depend on the surface properties of the solid. This work was applied to volcanic ash for the first time by Dr Claire Horwell in collaboration with Prof. Bice Fubini's group at the Università degli Studi di Torino. The research examined possible mechanisms of crystalline silica toxicity through the generation of free and surface radicals from volcanic ash particles.
Results of in vitro experiments show that respirable (<4 um)volcanic ash is capable of generating hydroxyl radicals which, in the lung, are capable of causing DNA damage and inflammation which, in turn, can lead to lung disease. Volcanic ash produced 2-3 times more hydroxyl radicals than a quartz standard of known toxicity (Min-U-Sil 5). No evidence was found to link the reactivity of respirable or bulk ash, as measured by generation of hydroxyl radicals and surface radicals, with the presence of cristobalite. The ash may be potentially harmful due to the presence of Fe2+ stabilised on the surface of particles. Iron, present on the surface of particles, is capable of catalysing reactions and producing free radicals. Radical release is high in freshly erupted samples and is affected by the oxidation and co-ordination state of iron, the freshness of sample surfaces and the surface area of ash particles (Horwell et al., in press, 2003b).
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