Exploratory Study of the Potential Airborne Health Hazard of Dusts Generated by Quarrying Volcanic Deposits

Abstract

Occupational exposure to dust generated by quarrying siliceous rocks (i.e. sandstone, coal) is a well documented respiratory hazard. Hazard of volcanic ash inhalation is also routinely studied (although less well understood), but the specific respiratory hazard of quarried volcanic deposits is entirely under-researched and is the focus of this study. The two main factors potentially implicated in respiratory toxicity of volcanic quarry dust are: i) crystalline silica content implicated in silicosis and lung cancer; and ii) iron-catalysed hydroxyl radical generation, implicated in inflammation and carcinogenesis. Twelve sites (in New Zealand, Montserrat and Greece), quarrying a range of volcanic deposits, were investigated and compared with volcanic ash samples (to test suitability as an analogue) and dust from non-volcanic quarries (greywacke and sandstone) in an investigation of the physicochemical characteristics which may influence particle surface reactivity. Samples of deposited dust (<1mm size fraction) were collected and 11 of these separated to ≤10μm for further analyses. Compositional analyses (XRF) showed the samples spanned the range of magmatic compositions from mafic to felsic (44-76 wt.% SiO2). The finest material was generated by drilling lava flows (8.3-27.5 cu.vol% <10 μm diameter particles in <1mm fraction), however, several other sample types (i.e. dust on processor) contained high levels of respirable material, akin to volcanic ash from equivalent eruption settings. SEM analyses confirmed particles to be blocky and angular, having aspect ratios between 0.59-0.70 (<10μm fraction). Crystalline silica content was highest (up to 28 wt. %) in dusts from intermediate and felsic quarries where lava domes (or collapse deposits) are mined. Similar levels were observed for dome-collapse ash and greywacke quarry dusts; however, the sandstone quarry dust was 99 wt.% crystalline silica. Hydroxyl radical generation was lower for quarried volcanic samples than for either volcanic ash or sandstone (significant to p≤0.01 for mafic ash/quarry dust). Haemolysis (erythrocyte membrane rupture, an indicator of quartz reactivity) was exhibited by six samples from three quarries, and comparable to the DQ12 quartz positive standard, when adjusted for surface area. These findings may be influenced by the presence of clays, however, as haemolytic samples included those with little crystalline silica. Airborne dust levels (both role-specific and ambient) were measured in the quarries and were mostly within international exposure limits, however, interpretations were limited by the duration of measurements so further work is required. Some workers’ shifts were longer than 8 hours, and workers on Montserrat may also be simultaneously exposed to volcanic
ashfall, which should be considered with respect to adherence to regulations in those quarries. Mitigation measures were variable and workers would benefit from better awareness regarding use of non-mandatory respiratory protection. Volcanic quarries pose a hazard distinct from volcanic ash and from non-volcanic quarries. Overall, hazard may be lower than for quarrying other rock types, but further research is needed to better constrain the potential hazards. Until then, a precautionary approach might be taken in quarries where respirable dust levels are high and deposits may contain crystalline silica or iron.