The in vitro respiratory toxicity of cristobalite-bearing volcanic ash

David E Damby,Fiona A Murphy,Claire J Horwell,Jennifer Raftis,Kenneth Donaldson

doi:10.1016/j.envres.2015.11.020

Abstract

Ash from dome-forming volcanoes poses a unique hazard to millions of people worldwide due to an abundance of respirable cristobalite, a crystalline silica polymorph. Crystalline silica is an established respiratory hazard in other mixed dusts, but its toxicity strongly depends on sample provenance. Previous studies suggest that cristobalite-bearing volcanic ash is not as bio-reactive as may be expected for a dust containing crystalline silica. We systematically address the hazard posed by volcanic cristobalite by analysing a range of dome-related ash samples, and interpret the crystalline silica hazard according to the mineralogical nature of volcanic cristobalite. Samples are sourced from five well-characterized dome-forming volcanoes that span a range of magmatic compositions, specifically selecting samples rich in cristobalite (up to 16wt%). Isolated respirable fractions are used to investigate the in vitro response of THP-1 macrophages and A549 type II epithelial cells in cytotoxicity, cellular stress, and pro-inflammatory assays associated with crystalline silica toxicity. Dome-related ash is minimally reactive in vitro for a range of source compositions and cristobalite contents. Cristobalite-based toxicity is not evident in the assays employed, supporting the notion that crystalline silica provenance influences reactivity. Macrophages experienced minimal ash-induced cytotoxicity and intracellular reduction of glutathione; however, production of IL-1β, IL-6 and IL-8 were sample-dependent. Lung epithelial cells experienced moderate apoptosis, sample-dependent reduction of glutathione, and minimal cytokine production. We suggest that protracted interaction between particles and epithelial cells may never arise due to effective clearance by macrophages. However, volcanic ash has the propensity to incite a low, but significant, and sample-dependent response; the effect of this response in vivo is unknown and prolonged exposure may yet pose a hazard.

Highlights

Given the established hazard posed by respirable crystalline silica (CS) in occupational settings, the presence of cristobalite, a CS polymorph, in ash emerged as a primary health concern during the 1980 eruption of Mount St
A bi-modal distribution arises from combining results from Fast Mobility Particle Sizer (FMPS) and Aerodynamic Particle Sizer (APS) (Fig. 1); this is likely due to instrumentation and is not considered further
The gradual slope towards the upper size cut-off ( $ 7.0 mm) is likely a physical artefact as the probability of re-suspension decreases towards the defined particle cut-off (6 mm)

Summary

Introduction

Given the established hazard posed by respirable crystalline silica (CS) in occupational settings, the presence of cristobalite, a CS polymorph, in ash emerged as a primary health concern during the 1980 eruption of Mount St. Eruptions worldwide, and is central to rapid hazard assessments carried out by the International Volcanic Health Hazard Network (e.g., Damby et al, 2013; Horwell et al, 2013a). Comprehensive risk assessments to determine the long-term risk of silicosis arising from chronic exposure to cristobalitebearing ash have been conducted only for the eruptions of Mount St. Helens and Soufrière Hills (Horwell and Baxter, 2006). As a non-occupational risk of silicosis had never been recognized prior to the Mount St. As a non-occupational risk of silicosis had never been recognized prior to the Mount St

Methods

Results

Conclusion