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

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.

Keywords: Air pollution; Free radicals; Haemolysis; Health hazard; Particle characterization; Volcanic ash.

Fig. 1

Locations of volcanic systems in Iceland relevant to this study. Central volcanoes/domains of volcanic systems from which ash was sourced are indicated by triangles or by a short line in case of large fissure eruptions. Also shown are towns (black or white circles) and ice caps (gray-white gradient-shaded areas). The Upper Pleistocene formation boundary (dark gray shaded area) is adapted from Thordarson and Höskuldsson [30]

Fig. 2

IVHHN rapid-response protocol used to assess the health hazard posed by volcanic ash. Circled analyses were performed for this study. No leachate analyses or cell-based toxicity experiments were conducted as samples were not collected fresh. Protocol adapted from Damby et al. [15]

Fig. 3

Bulk compositions of volcanic ash samples. Sample compositions are plotted according to magma type as total alkali (K₂O + Na₂O) versus silica (SiO₂). Data for Snæfellsjökull sample (Snae-1) from Martin and Sigmarsson [77]

Fig. 4

Selected scanning electron micrographs of volcanic ash samples. (a) Askja-55d, (b) Askja-56a, (c) Askja-59b, (d) Hekla-1980, (e) Hekla-4, (f) Katla-1755, (g) Laki-SnVII, (h) Orae-s1, (i) Orae-s13, (j) Reyk-1227, (k) Snae-1 and (l) Veid-1477. All images were collected at 8.0 kV and ~14 mm working distance

Fig. 5

Transmission electron microscope analysis of respirable material in select volcanic ash samples. TEM data of fiber-like particles in Hekla-4 (a) and Laki-SnVII (b-d) with corresponding selected area diffraction patterns and chemical (EDS) analyses (middle and right columns of panels, respectively): (a) completely amorphous fiber dominated by oxygen, silicon, aluminum, potassium, calcium and iron; (b) completely amorphous fiber consisting of predominantly silicon and oxygen with lesser amounts of aluminum, iron and calcium; (c) semi-crystalline fiber consisting of carbon, sodium and oxygen; (d) well-crystalline fiber predominantly comprised of silicon and oxygen with calcium, iron and magnesium, and lesser amounts of titanium

Fig. 6

Comparison of surface reactivity for ground and un-ground volcanic ash samples. Production of hydroxyl radicals (HO^•) was measured by spin-trapping and electron paramagnetic resonance after 30 min through replication of the iron-catalyzed Fenton reaction. Grinding was intended to restore the sample surface in order to represent HO^• production from freshly collected samples. Data are presented per unit surface area. Error bars represent standard error (n = 3)

Fig. 7

Comparison of hydroxyl radical production with removable surface iron for select volcanic ash samples. Hydroxyl radicals (HO^•) produced through replication of the iron-catalyzed Fenton reaction by unground samples were determined by spin-trapping and electron paramagnetic resonance after 30 min. The total amount of available iron extracted from unground samples by chelation is presented for a time-point of 7 days. Hydroxyl radical generation and iron release are both expressed per unit surface area. The three comparative samples have been used previously [54] and were reanalyzed for this study: Mt. Etna, Sicily (2002, basaltic), Soufrière Hills, Montserrat (5/6/99, andesitic), Cerro Negro, Nicaragua (1995, basaltic)

Fig. 8

Hemolytic potential of selected volcanic ash samples. Dose-dependent hemolysis as a percentage of complete cell lysis (0.1% Triton X-100) for human red blood cells treated with 0.31 to 1 mg ml⁻¹ sample concentrations of volcanic ash. TiO₂ and DQ12 (quartz) are negative and positive particle controls, respectively. Error bars are the standard error of the mean (n = 3)