Volcanic ash in the airways: compositional controls on inflammation, immune modulation, and infection risk

INTRODUCTION: More than one billion people live within 100 km of an active volcano, yet the respiratory hazard of ash resists generalization. Bulk composition modulates eruption parameters, therefore respirability, and determines the availability of crystalline silica and labile metals in basaltic ash. AREAS COVERED: We review the health-pertinent properties of volcanic ash, consistently reported symptoms of acute exposure, and the thin, confounded evidence for chronic disease, where co-exposure to volcanic gases and aerosols impairs attribution. We develop an underexplored possibility: volcanic environments increase the risk of environmentally acquired lung infection via ash fomites carrying viable bacteria, innate defense impairment, including iron-dependent nutritional immunity, and selection for pathogen metal-resistance systems in metal-rich volcanic environments. Nontuberculous mycobacterial lung disease in Hawai'i and an exploratory country-level comparison of epidemiology metrics with volcanism test whether the disease axis is visible in existing data. EXPERT OPINION: Volcanic ash hazards are eruption-specific and crystalline silica and labile metals are joined by a scarcely tested third. That is, environmentally acquired bacterial lung infections are higher in 'volcanic' countries and account for a greater share of respiratory infections; both outcomes are ecological and hypothesis-generating. The infectious disease pathway and health effects of chronic exposure remain the least constrained assessment element.