Spatial distribution and physicochemical properties of respirable volcanic ash from the 16-17 August 2006 Tungurahua eruption (Ecuador), and alveolar epithelium response in-vitro
BackgroundTungurahua volcano (Ecuador) intermittently emitted ash between 1999 and 2016, enduringly affecting the surrounding rural area and its population, but its health impact remains poorly documented. ObjectivesWe aim at assessing the respiratory health hazard posed by the 16-17 August 2006 most intense eruptive phase of Tungurahua. MethodsBased on detailed field surveys and grain size analyses, we mapped the spatial distribution of the health-relevant ash size fractions produced by the eruption in the area impacted by ash fallout. We used Scanning Electron Microscopy and Raman Spectroscopy to quantify the mineralogy, composition, surface texture and morphology of a respirable ash sample isolated by aerodynamic separation. The cytotoxicity and pro-inflammatory potential of this respirable ash towards lung tissues was assessed in-vitro using A549 alveolar epithelial cells, by Electron Microscopy and biochemical assays (LDH assay, RT-qPCR, multiplex immunoassays). ResultsThe eruption produced a high amount of inhalable and respirable ash (12.0-0.04 kg/m2 of sub-10 {micro}m and 5.3-0.02 kg/m2 of sub-4 {micro}m ash deposited). Their abundance and proportion vary greatly across the deposit within the first 20 km from the volcano. The respirable ash is characteristic of an andesitic magma and no crystalline silica is detected. Morphological features and surface textures are complex and highly variable, with few fibres observed. In-vitro experiments show that respirable volcanic ash are internalized by A549 cells and processed in the endosomal pathway, causing little cell damage, but some changes in cell morphology and membrane texture. The ash trigger a weak pro-inflammatory response. DiscussionThese data provide the first understanding of the respirable ash hazard near Tungurahua, and the extent to which it varies spatially in a fallout deposit. Given the long exposure duration of the surrounding population, the chronic effects of this inhalable, weakly bio-reactive ash on health could be further investigated.