Spatial Distribution and Physicochemical Properties of Respirable Volcanic Ash From the 16–17 August 2006 Tungurahua Eruption (Ecuador), and Alveolar Epithelium Response In‐Vitro

Tungurahua 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. We aim to assess the respiratory health hazard posed by the 16–17 August 2006 most intense eruptive phase of Tungurahua. We mapped the spatial distribution of the health‐relevant ash size fractions produced by the eruption in the area impacted by ash fallout. We quantified the mineralogy, composition, surface texture, and morphology of a respirable ash sample isolated by aerodynamic separation. We then assessed the cytotoxicity and pro‐inflammatory potential of this respirable ash toward lung tissues in‐vitro using A549 alveolar epithelial cells, by electron microscopy and biochemical assays. The eruption produced a high amount of inhalable and respirable ash (12.0–0.04 kg/m2 of sub‐10 μm and 5.3–0.02 kg/m2 of sub‐4 μm 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 fibers observed. In‐vitro experiments show that respirable volcanic ash is internalized by A549 cells and processed in the endosomal pathway, causing little cell damage, but resulting in changes in cell morphology and membrane texture. The ash triggers a weak pro‐inflammatory response. These data provide the first understanding of the respirable ash hazard near Tungurahua and the extent to which it varies spatially in a fallout deposit. Plain Language Summary Much is left to understand on the health hazard related to inhaling volcanic ash. This is due to the high variability in ash properties from one volcanic eruption to another. In our new study, we focus on a key volcanic environment, the region of Tungurahua volcano in the Eastern Andean Cordillera of Ecuador, where populations were affected by a long‐lasting eruption between 1999 and 2016. Despite being persistently impacted by volcanic ash, about 32,000 people in rural communities chose to remain on their land and developed a remarkable socio‐economic resilience in face of the volcanic risk. The consequence was that they were chronically exposed to airborne volcanic ash via inhalation for a long period of time. Sparse data exist on the health impact of the Tungurahua eruption on surrounding popu