Exploring the link between surface structures and toxicity in mineral particles: Case study of induced and intrinsic toxicity in quartz

A proportion of dust that is inhaled consists of particles that are small enough to penetrate deep into the lungs. Most particles are relatively harmless and on being recognised as foreign are removed from the lung by specialised mechanisms. Occasionally particles are resistant to removal and can set up toxic reactions. Perhaps the best known case is that of asbestos fibres that can ultimately lead to the lung disease asbestosis and the lung cancer mesothelioma. Other harmful particulates are found in diesel fumes. Dust created by industries such as mining, quarrying and sandblasting is also associated with lung disease including silicosis and lung cancer. In this case the culprit is usually quartz, the second most common mineral in the environment and normally relatively harmless unless inhaled in large doses. The feature of importance to this project is that quartz is variable in its toxicity. There are examples of quartz dust that are highly toxic and others with relatively low toxicity. Toxicity can also be induced by mechanically fracturing quartz grains, as happens in the process of breaking rocks for mining or impacting at high pressure during sandblasting. This toxicity is transient and decays rapidly over a few hours to one or two days. It can be shown that for quartz, at least, the process leading to a toxic response such as inflammation begins at the surface of the particle. Coating the surface can reduce or eliminate the toxicity which can then be restored when the coating is removed. This suggests that the surfaces of the most toxic samples of quartz will differ in some detectable way from the surface of the least toxic samples. This project will seek to locate any such differences by examining quartz particles known to have a range of different toxicities. Several features have been suggested including reaction with water molecules at the surface, the presence of aluminium or iron impurities on surface sites, and the presence of surface free radicals. Hitherto free radicals have been successfully correlated with the transient toxicity of fractured quartz but not with the long term inherent differences in toxicity suggesting that other characteristics of the quartz surface are likely to be important. The project will involve applying the methodologies of surface chemistry to detecting elemental and molecular structures on the surface of different samples of quartz, and by desorbing molecules from the surface by heating prior to analysis. The same samples will also be characterised at the atomic level using atomic force microscopy in which images of the surface may reveal differences in surface topography. Experiments will be conducted to test whether additional toxicity can be induced in quartz samples with already high intrinsic toxicity. To date such experiments have not been conducted. The outcome of the research should be a better understanding of the mechanisms involved and thus better information for regulators and policy makers in the field of environmental and occupational exposure to dusts.