In-vitro toxicology of respirable iron-rich particles relevant to mining industry: a high throughput framework for interpreting environmental particulate matter toxicity

Abstract

This project investigated the cytotoxicity profiles and toxicological properties of inhalable iron-rich particles generated by mining activity. National Environment Protection Measure (NEPM) ambient air quality regulations specifically regulate sub-10 µm (PM10) and sub-2.5 µm (PM2.5) diameter particle fractions corresponding to thoracic and respirable lung penetration, respectively. However, atmospheric concentrations of fugitive iron-rich particulates in iron ore mining and processing associated settlements raised concerns that NEPM limits may inadequately address the specific toxicological profile of iron-rich PM10 and potentially adsorbed organics in these regions. To address this, comparative cytotoxicity experiments were carried out in-vitro using a variety of particulate standards, featuring other frequently studied metal-oxides, to help bridge in-vivo and epidemiological knowledge in the literature with in-vitro toxicological results. This also required the development of a novel framework to interpret physical and physiological characteristics of coarse, poorly soluble metal-oxide particles by conducting a critical systematic literature review.Analysis by the ChemCentre, WA was taken into account with relation to potentially absorbed organics and the influence of Polycyclic Aromatic Hydrocarbons (PAHs) investigated.The protocols developed by this project are applicable to high-throughput assessment of particulate matter generated by mining activity, having defined methodology to rapidly acquire sufficient quantities of PM10 for assays which can be multiplexed and the effects of particulate interference on assays minimised. This includes the integration of non-destructive sterilisation techniques, physical characterising by particle-sizing, particle solubility analysis and observation of particle morphology by electron microscopy and elemental analysis. Epithelial (A549), fibroblast (LL24) and monocyte differentiated macrophage (U937) cell lines were tested to build a picture of particulate effects on the major lung cell types in the lung parenchyma; the alveolar epithelium, connective tissue and immune system.The effect of lung fluid surfactants on cytotoxicity was determined, and advanced tissue culture methods were trialled to improve the differentiation between particles provided by the endpoints.ii The ore samples from the Mining Area C (MAC), Yandi and Newman Hub mines in the Pilbara region were found to have an effect comparable to the cytotoxicity of micron-size iron oxide standards and selected standards of titanium dioxide, silicon dioxide and carbon black, whereas copper oxide was found to have some ten-fold greater cytotoxicity across the cell lines. However cytotoxicity as a principle differentiator of toxicity was found to be insufficient in differentiating the physiological response to iron-rich PM10 and insoluble metal-oxide standards. At high concentrations the dose-response relationship plateaued at a maximum value for iron-oxide standards and iron ore samples in the A549 and LL2...