Assessment of the potential respiratory hazard of volcanic ash from future Icelandic eruptions: a study of archived basaltic to rhyolitic ash samples

Our plain-English summary of Assessment of the potential respiratory hazard of volcanic ash from future Icelandic eruptions: a study of archived basaltic to rhyolitic ash samples, by D.E. Damby, C.J. Horwell, G. Larsen, et al (Environmental Health, 2017).

The study

• Authors: D.E. Damby, C.J. Horwell, G. Larsen, T. Thordarson, M. Tomatis, B. Fubini, K. Donaldson
• Journal: Environmental Health
• Published: 2017;16(1):98
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The eruptions of Eyjafjallajökull (2010) and Grímsvötn (2011), Iceland, triggered immediate, international consideration of the respiratory health hazard of inhaling volcanic ash, and prompted the need to estimate the potential hazard posed by future eruptions of Iceland's volcanoes to Icelandic and Northern European populations.

Methods: A physicochemical characterization and toxicological assessment was conducted on a suite of archived ash samples spanning the spectrum of past eruptions (basaltic to rhyolitic magmatic composition) of Icelandic volcanoes following a protocol specifically designed by the International Volcanic Health Hazard Network.

Results: Icelandic ash can be of a respirable size (up to 11.3 vol.% < 4 μm), but the samples did not display physicochemical characteristics of pathogenic particulate in terms of composition or morphology. Ash particles were generally angular, being composed of fragmented glass and crystals. Few fiber-like particles were observed, but those present comprised glass or sodium oxides, and are not related to pathogenic natural fibers, like asbestos or fibrous zeolites, thereby limiting concern of associated respiratory diseases. None of the samples contained cristobalite or tridymite, and only one sample contained quartz, minerals of interest due to the potential to cause silicosis. Sample surface areas are low, ranging from 0.4 to 1.6 m2 g-1, which aligns with analyses on ash from other eruptions worldwide. All samples generated a low level of hydroxyl radicals (HO•), a measure of surface reactivity, through the iron-catalyzed Fenton reaction compared to concurrently analyzed comparative samples. However, radical generation increased after 'refreshing' sample surfaces, indicating that newly erupted samples may display higher reactivity. A composition-dependent range of available surface iron was measured after a 7-day incubation, from 22.5 to 315.7 μmol m-2, with mafic samples releasing more iron than silicic samples. All samples were non-reactive in a test of red blood cell-membrane damage.

Conclusions: The primary particle-specific concern is the potential for future eruptions of Iceland's volcanoes to generate fine, respirable material and, thus, to increase ambient PM concentrations. This particularly applies to highly explosive silicic eruptions, but can also hold true for explosive basaltic eruptions or discrete events associated with basaltic fissure eruptions.

In plain English

This laboratory study tested 14 archived ash samples from 11 past eruptions at 8 Icelandic volcanoes to estimate the breathing hazard of future eruptions. The samples ranged from basaltic to rhyolitic ash and were tested with a protocol of the International Volcanic Health Hazard Network. This is not a study of asbestos exposure. The authors measured particle size, shape, crystalline silica, surface area, free radical production, surface iron and damage to red blood cells. In two samples, Laki-SnVII and Hekla-4, particles under 4 μm (respirable size) made up 5.1 and 11.3 percent by volume of the ash fraction under 2 mm. Fiber-like particles were rare. The crystalline fibers seen were not related to asbestiform minerals or fibrous zeolites. One sample contained quartz; none contained cristobalite or tridymite. All samples produced low hydroxyl radical levels, which rose after grinding. None of the tested samples made red blood cells burst in a laboratory assay. The authors concluded that the main particle concern is fine, respirable ash raising airborne particle levels. They noted that weathering of the old samples limited toxicity testing, and that gases were not studied.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory physicochemical characterization and toxicological screening of archived volcanic ash samples, following a rapid-assessment protocol of the International Volcanic Health Hazard Network (IVHHN)
• Who was studied: 14 archived tephra (ash) samples from 11 eruptions at 8 central volcanoes in Iceland. The eruptions ranged from about 4.2 ka BP (Hekla-4) to 1980 (Hekla-1980). Not every analysis was done on every sample because of limited sample mass.
• Exposure: Icelandic volcanic ash spanning basaltic to rhyolitic magma compositions, analyzed as the less than 1 mm fraction. No asbestos was studied; asbestos is mentioned only as a comparison for the fiber-like particles found.
• Main results:
  • Most samples were coarse grained. In Laki-SnVII, particles under 4 μm made up 5.1 percent by volume of the ash fraction under 2 mm; in Hekla-4 they made up 11.3 percent. The authors described both samples as containing abundant respirable material.
  • Fibers were rare but present in both samples examined by TEM (Hekla-4 and Laki-SnVII). Laki-SnVII contained three kinds of fiber-like particles: amorphous, semi-crystalline (sodium and oxygen), and well-crystalline (silicon and oxygen). Based on database indexing, the well-crystalline fibers were not related to asbestiform minerals or fibrous zeolites. Hekla-4 contained only amorphous fiber-like particles.
  • Almost all samples lacked detectable crystalline silica. The exception was Snae-1, which contained detectable quartz. No sample contained cristobalite or tridymite.
  • Specific surface areas ranged from 0.4 to 1.6 m2 per g. Hekla-4 had the largest surface area.
  • All samples generated hydroxyl radicals, at low levels compared with the comparison ash samples analyzed at the same time. All samples generated more radicals after grinding than as collected.
  • Available surface iron after 7 days ranged from 22.5 to 315.7 μmol per m2, with mafic (basaltic) samples releasing more iron than silicic samples. There was no correlation between the iron released and radical generation. Askja-59b, a dacitic sample, generated the most hydroxyl radicals.
  • In a laboratory hemolysis assay on the selected samples tested, none caused red blood cell lysis compared with the negative particle control. All were far less reactive than the quartz positive control.
• The authors' conclusion: The authors concluded that future explosive Icelandic eruptions across the compositional range could produce respirable ash that may raise airborne particle levels. They expected the ash to have low crystalline silica content unless an existing dome is disrupted, a low surface area, and insubstantial fiber-like particles. They suggested that fresh ash be analyzed during future eruptions.
• Limitations the authors state:
  • Full toxicological testing was not done because some samples were thousands of years old and had been weathered, which affects toxicity.
  • Only 1 to 3 samples were taken per eruption, mostly close to the source. The particle size results therefore indicate potential rather than the finest ash produced.
  • There was not enough of the quartz-containing sample (Snae-1) for quantitative analysis, and limited sample mass restricted the analyses done on some samples.
  • The two toxicity screening endpoints could not predict how toxicity might vary in ash from future eruptions.
  • Volcanic gas and soluble-species (leachate) hazards were not addressed.

Topics

Medical terms in this study, explained in our Lexicon: Zeolite, Silicosis, Hydroxyl Radical, Surface Reactivity, Fenton Reaction.

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