Ash & Aerosol Characterization

Detailed and accurate characterization of the size, composition and grain-size distribution of particles is a crucial step in the determination of the potential toxicity of volcanic ash and aerosols. Most respiratory pathogenic (disease-causing) reactions occur in the alveolar region of the lung which can only be penetrated by fine particles usually classed as 'respirable' particles (< 4 um aerodynamic diameter). If an eruption produces particles which are substantially larger than respirable particles, the chances of pathogenic reactions occurring are much reduced.

Similarly, the composition of volcanic particles may well be of great importance in the determination of their toxicity. 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 cristobalite (Horwell et al. 2003). Cristobalite is considered to have a greater potential to cause lung disease than the more common silica polymorph, quartz.
 

The quantity of respirable material in the bulk ash is also of importance and is measured primarily through grain-size distribution analyses. It is now known that around 11 wt.% of the Soufriere Hills dome-collapse ash is of respirable size and that around 15 wt.% of that respirable ash is cristobalite (Horwell et al. 2003).

Without this detailed examination of the morphological and compositional characteristics of volcanic ash, the planning of toxicological (in vivo) studies of the effects of volcanic ash in the lung can be impaired.