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

吸入的一部分灰尘由小到足以深入肺部的颗粒组成。大多数颗粒相对无害，被识别为异物后，通过专门的机制从肺中清除。有时颗粒难以清除，并可能引起毒性反应。也许最著名的案例是石棉纤维，它最终会导致肺病石棉沉滞症和肺癌间皮瘤。其他有害颗粒物存在于柴油烟雾中。采矿、采石和喷砂等行业产生的粉尘也与肺病有关，包括矽肺和肺癌。在这种情况下，罪魁祸首通常是石英，这是环境中第二常见的矿物质，除非大量吸入，否则通常相对无害。本项目的重要特征是石英的毒性可变。有一些石英粉尘的例子是高毒性的，而其他的毒性相对较低。机械破碎石英颗粒也会引起毒性，如在采矿过程中破碎岩石或在喷砂过程中高压冲击时发生的情况。这种毒性是短暂的，在几小时到一两天内迅速衰减。可以表明，至少对于石英，导致毒性反应（如炎症）的过程始于颗粒表面。涂覆表面可以减少或消除毒性，然后当涂层被去除时可以恢复毒性。这表明，石英中毒性最大的样品的表面与毒性最小的样品的表面在某种可检测的方式上有所不同。该项目将通过检查已知具有一系列不同毒性的石英颗粒来寻找任何此类差异。已经提出了几个特征，包括在表面与水分子反应，在表面位点上存在铝或铁杂质，以及存在表面自由基。已成功地将过氧化氢自由基与断裂石英的瞬时毒性相关联，但与毒性的长期固有差异无关，这表明石英表面的其他特性可能很重要。该项目将涉及应用表面化学方法来检测不同石英样品表面的元素和分子结构，并在分析前通过加热使分子从表面脱附。同样的样品也将在原子水平上使用原子力显微镜进行表征，其中表面的图像可以揭示表面形貌的差异。将进行实验，以测试是否可以在已经具有高内在毒性的石英样品中诱导额外的毒性。到目前为止，还没有进行过这样的实验。研究的结果应当是更好地了解所涉机制，从而为环境和职业接触粉尘领域的管理者和决策者提供更好的信息。

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.