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

Nonlinearity of the Upconversion Response of Er3+ in Y2TiO5:Er3+,Yb3+ Ceramics When Varying the Wavelength of Incident NIR Excitation Radiation

The upconversion response of Er3+ sensitized by Yb3+ in various crystalline hosts and illuminated with a laser light at around 980 nm revealed certain spectral shapes that are typical for each of the crystalline matrices containing the dopants. The purpose of this work was to measure the upconversion response of Er3+ as a dopant in Y2TiO5, sensitized by Yb3+, at different concentrations relative to the substituted Y3+ ion, and to reveal the subtleties of the mechanisms of the energy transfers between them and the lattice. Therefore, we synthesized Y2TiO5 ceramic samples doped with different concentrations of Er3+ and Yb3+, below 10% (mol), in order to minimize the distortion of the lattice. The oxide powders, obtained using the sol-gel method, as well as the ceramics were structurally and morphologically characterized using an X-ray diffraction analysis and scanning electron microscopy. When the ceramic samples were irradiated with an NIR laser light, it was found that, at a wavelength variation of only 2 nm of the incident radiation, from 973.5 nm to 975.5 nm, the upconversion spectra differed significantly. This nonlinearity is notable because it is not present in the case of other crystalline host matrices studied by us since the literature lacks information on this subject. We also correlated this effect with the simulated distribution of the average distances between Er3+ and Yb3+ ions in the host matrix.

Confocal microscopy 3D imaging and bioreactivity of La Palma volcanic ash particles

In September 2021 an eruption began of Cumbre Vieja, La Palma (Spain) that lasted 3 months. Previous studies have shown that volcanic ash particles can be associated with adverse effects on human health however, the reasons for this are unclear. Particle shape has been shown to contribute to cellular uptake in prostate cancer cells. Hence we aimed to study 3D structure, elemental composition and effects on cultured lung cells of particles collected from the La Palma volcanic eruption. 3D imaging of PM10 sized and below particles was performed using a LEXT OLS4100 confocal microscope (Olympus Corporation, Japan). A Zeiss EVO 50 (Carl Zeiss AG, Germany) Scanning Electron Microscope (SEM) was used to assess elemental composition. In addition, volcanic particle concentration dose response for pneumococcal adhesion to A549 human alveolar epithelial cells was investigated. Confocal microscopy showed that some PM10 and below sized particles had sharp or angular 3D appearance. SEM x-ray analysis indicated silicate particles with calcium, aluminium and iron. We observed increased colony forming units indicating increased Pneumococcal adhesion due to exposure of cells to volcanic particles. Thus in addition to the toxic nature of some volcanic particles, we suggest that the observed sharp surface particle features may help to explain adverse health effects associated with volcanic eruptions.

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.

Development of a simulated lung fluid leaching method to assess the release of potentially toxic elements from volcanic ash

Freshly erupted volcanic ash contains a range of soluble elements, some of which can generate harmful effects in living cells and are considered potentially toxic elements (PTEs). This work investigates the leaching dynamics of ash-associated PTEs in order to optimize a method for volcanic ash respiratory hazard assessment. Using three pristine (unaffected by precipitation) ash samples, we quantify the release of PTEs (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, Zn) and major cations typical of ash leachates (Mg, Na, Ca, K) in multiple simulated lung fluid (SLF) preparations and under varying experimental parameters (contact time and solid to liquid ratio). Data are compared to a standard water leach (WL) to ascertain whether the WL can be used as a simple proxy for SLF leaching. The main findings are: PTE concentrations reach steady-state dissolution by 24 h, and a relatively short contact time (10 min) approximates maximum dissolution; PTE dissolution is comparatively stable at low solid to liquid ratios (1:100 to 1:1000); inclusion of commonly used macromolecules has element-specific effects, and addition of a lung surfactant has little impact on extraction efficiency. These observations indicate that a WL can be used to approximate lung bioaccessible PTEs in an eruption response situation. This is a useful step towards standardizing in vitro methods to determine the soluble-element hazard from inhaled ash.

Assessment of the potential for in-plume sulphur dioxide gas-ash interactions to influence the respiratory toxicity of volcanic ash

BACKGROUND

Volcanic plumes are complex environments composed of gases and ash particles, where chemical and physical processes occur at different temperature and compositional regimes. Commonly, soluble sulphate- and chloride-bearing salts are formed on ash as gases interact with ash surfaces. Exposure to respirable volcanic ash following an eruption is potentially a significant health concern. The impact of such gas-ash interactions on ash toxicity is wholly un-investigated. Here, we study, for the first time, whether the interaction of volcanic particles with sulphur dioxide (SO₂) gas, and the resulting presence of sulphate salt deposits on particle surfaces, influences toxicity to the respiratory system, using an advanced in vitro approach.

METHODS

To emplace surface sulphate salts on particles, via replication of the physicochemical reactions that occur between pristine ash surfaces and volcanic gas, analogue substrates (powdered synthetic volcanic glass and natural pumice) were exposed to SO₂ at 500 °C, in a novel Advanced Gas-Ash Reactor, resulting in salt-laden particles. The solubility of surface salt deposits was then assessed by leaching in water and geochemical modelling. A human multicellular lung model was exposed to aerosolised salt-laden and pristine (salt-free) particles, and incubated for 24 h. Cell cultures were subsequently assessed for biological endpoints, including cytotoxicity (lactate dehydrogenase release), oxidative stress (oxidative stress-related gene expression; heme oxygenase 1 and NAD(P)H dehydrogenase [quinone] 1) and its (pro-)inflammatory response (tumour necrosis factor α, interleukin 8 and interleukin 1β at gene and protein levels).

RESULTS

In the lung cell model no significant effects were observed between the pristine and SO₂-exposed particles, indicating that the surface salt deposits, and the underlying alterations to the substrate, do not cause acute adverse effects in vitro. Based on the leachate data, the majority of the sulphate salts from the ash surfaces are likely to dissolve in the lungs prior to cellular uptake.

CONCLUSIONS

The findings of this study indicate that interaction of volcanic ash with SO₂ during ash generation and transport does not significantly affect the respiratory toxicity of volcanic ash in vitro. Therefore, sulphate salts are unlikely a dominant factor controlling variability in in vitro toxicity assessments observed during previous eruption response efforts.

Respiratory hazard assessment of combined exposure to complete gasoline exhaust and respirable volcanic ash in a multicellular human lung model at the air-liquid interface

Communities resident in urban areas located near active volcanoes can experience volcanic ash exposures during, and following, an eruption, in addition to sustained exposures to high concentrations of anthropogenic air pollutants (e.g., vehicle exhaust emissions). Inhalation of anthropogenic pollution is known to cause the onset of, or exacerbate, respiratory and cardiovascular diseases. It is further postulated similar exposure to volcanic ash can also affect such disease states. Understanding of the impact of combined exposure of volcanic ash and anthropogenic pollution to human health, however, remains limited. The aim of this study was to assess the biological impact of combined exposure to respirable volcanic ash (from Soufrière Hills volcano (SHV), Montserrat and Chaitén volcano (ChV), Chile; representing different magmatic compositions and eruption styles) and freshly-generated complete exhaust from a gasoline vehicle. A multicellular human lung model (an epithelial cell-layer composed of A549 alveolar type II-like cells complemented with human blood monocyte-derived macrophages and dendritic cells cultured at the air-liquid interface) was exposed to diluted exhaust (1:10) continuously for 6 h, followed by immediate exposure to the ash as a dry powder (0.54 ± 0.19 μg/cm² and 0.39 ± 0.09 μg/cm² for SHV and ChV ash, respectively). After an 18 h incubation, cells were exposed again for 6 h to diluted exhaust, and a final 18 h incubation (at 37 °C and 5% CO₂). Cell cultures were then assessed for cytotoxic, oxidative stress and (pro-)inflammatory responses. Results indicate that, at all tested (sub-lethal) concentrations, co-exposures with both ash samples induced no significant expression of genes associated with oxidative stress (HMOX1, NQO1) or production of (pro-)inflammatory markers (IL-1β, IL-8, TNF-α) at the gene and protein levels. In summary, considering the employed experimental conditions, combined exposure of volcanic ash and gasoline vehicle exhaust has a limited short-term biological impact to an advanced lung cell in vitro model.