# Iron-Rich Magnetic Coal Fly Ash Particles Induce Apoptosis in Human Bronchial Cells
## 1 Introduction  
Svalbard is a small Norwegian archipelago located north of mainland Europe in the Arctic Circle. At the beginning of the 20 th century, coal deposits were discovered, and since then coal mining has been a major industry on the islands [1]. The sole source of electricity for the islands comes from the coal-fired power station located on the outskirts of Longyearbyen. The coal is locally sourced from the two operating mines on Svalbard, which are run by Store Norske. Only a small portion of the coal is used in the small power station, the remainder is exported to mainland Europe to countries such as Germany, the Netherlands, and Denmark [2]. The coal mined on Svalbard is from the Paleocene epoch (66-56 Ma). Coal deposits on the islands from other geological periods are too small to be mined commercially [2]. The Cenozoic Central Basin of Svalbard contains both the mined coal deposits, Gruve 7 and Svea Nord, which are in the Todalen Member. This is mostly composed of lessthan 60 metres of thick rhythmic and coarsening upwards successions of shale-siltstone-sandstone, capped by either coal or clay ironstone [3]. The Longyearbyen Power Station burns 22,000 tons of coal each year from the two mines on Svalbard. Particulate matter (PM) released from the power station are categorised as being either \"inhalable\" (diameter less than 10 \(\upmu\)m (PM\({}_{10}\)) or \"respirable\" particles (diameter less than 2.5 \(\upmu\)m (PM\({}_{2.5}\)) [4]. Coal fly ash (CFA) is the combustion-derived PM that is formed as a by-product of fossil fuel combustion from the inorganic (i.e., incombustible) minerals present. CFA contributes to the burden of air pollution as a result of its direct release from power station stacks, or released indirectly from waste storage piles by wind resuspension [5]. During coal combustion, depending on the temperatures reached, mineral impurities can melt to form glass droplets and are carried along the hot gas stream in the furnace flue [6]. As the melted material travels, it cools and solidifies into multi-sized \"dirty glass\" spheres, which can be identified as CFA particles. The properties of the CFA depend on the physicochemical properties of the original coal, particle size, combustion processes, and the type of ash collector [7]. The inhalable fraction of most CFA consists predominantly of uniformly spherical particles but can also contain smaller agglomerates and fragments within the PM\({}_{10}\) range. Smaller CFA spheres are typically 2-3 \(\upmu\)m in diameter but can aggregate to form larger structures [8]. Ferrous minerals can either be original coal minerals that failed to melt during combustion but might have undergone some geochemical change, or minerals that crystallised out of the glass in the CFA. The presence of crystallised \"dendritic\" iron oxides inside CFA is well established, however, the crystallisation sequence is still unclear [6]. The oxidative capacity of iron oxides in CFA has been well documented, stating that Fenton-like reactions result in reactive oxygen species (ROS) generation, specifically the hydroxyl radical (\(\bullet\)OH) [9]. PM\({}_{10}\) CFA can enter the respiratory tract with the smaller PM (<2.5 \(\upmu\)m) able to penetrate deep into the lungs [8]. Here, ROS generation caused by the CFA could cause significant damage to bronchial epithelial cells lining the respiratory tract.  
In this study, we used a variety of geochemistry techniques to characterise the physicochemical properties of CFA collected in Svalbard. The characterised size fractions of PM10 CFA were put through a hierarchy of acellular in vitro bioreactivity assays that determine the presence of ROS. The bioreactivity of CFA samples was determined by using in vitro, three-dimensional, human-derived lung cell cultures of the bronchial epithelium. These results could provide fundamental data for the development of storage protocols and health risk assessments with respect to Svalbard CFA.