Paper No. 5
Presentation Time: 2:45 PM
INTEGRATING MINERALOGY, GEOCHEMISTRY AND TOXICOLOGY FOR THE RAPID DETERMINATION OF THE RESPIRATORY HEALTH HAZARD OF VOLCANIC ASH: RESULTS FROM 10 ERUPTIONS
HORWELL, Claire, Institute of Hazard, Risk & Resilience, Department of Earth Sciences, Durham University, Science Labs, South Road, Durham, DH1 3LE, United Kingdom, BAXTER, Peter J., Institute of Public Health, University of Cambridge, Cambridge, United Kingdom, WILLIAMSON, Ben, Camborne School of Mines, School of Geography, Archaeology and Earth Resources, University of Exeter, Cornwall Campus, Penryn, Cornwall, TR10 9EZ, United Kingdom, DONALDSON, Ken, The University of Edinburgh/MRC Centre for Inflammation Research, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh, EH16 4TJ, United Kingdom and TETLEY, Terry, National Heart and Lung Institute, Imperial College London, Dovehouse Street, London, SW3 6LY, United Kingdom, claire.horwell@durham.ac.uk
Following epidemiological, clinical, toxicological and mineralogical work carried out on ash from Mt St Helens, USA and Sakurajima, Japan in the 1980s, dedicated research on the respiratory health hazards of volcanic ash resumed in 1995 at the onset of eruptions at Soufrière Hills, Montserrat (still ongoing today) where, in addition to abundant, potentially-carcinogenic crystalline silica, it was recognised that reactive iron on the particle surfaces could provide a mechanism for toxicity. Here we present a summary of detailed studies done by our group and collaborators on ash from 10 volcanoes which have erupted a range of ash compositions (mafic to highly silicic). The studies followed a protocol designed specifically for rapid analysis of ash for the assessment of respiratory health hazard. The work combines physico-chemical characterisation of ash with toxicological assays, enabling an informed ‘health message’ to be produced which is rapidly disseminated to hazard managers.
Our analyses show that volcanic ash generated from the collapse of lava domes contains the most cristobalite (the dominant silica polymorph) but also that efficient fragmentation during collapse generates abundant inhalable material. Particularly fine ash is also produced through interaction of magma with water (phreatomagmatic activity) e.g. at Mt Vesuvius in AD79. Basaltic eruptions usually generate coarser ash but the high iron content of the magma correlates with increased iron-catalysed surface reactivity (measured through generation of the deleterious hydroxyl radical). Many volcanoes produce fibre-like particles but we have only observed these as rare occurrences amongst ‘normal’ angular, blocky ash particles.
Our toxicological results concur with the overall view of more detailed studies at Mt St Helens and Soufrière Hills: cristobalite-rich ash does not appear to be as toxic as some silica-rich dusts. However we do see evidence of some pro-inflammatory potential. We have found that cristobalite toxicity may be impaired because of substituted cations (particularly Al) in the crystal structure and because the surfaces of cristobalite particles may be occluded by coatings of glass or adhered mineral grains.
