Institute of Hazard, Risk & Resilience, Department of Earth Sciences, Durham University, Science Labs., South Road, Durham DH1 3LE, UK.
Part Fibre Toxicol. 2012 Nov 19;9:44. doi: 10.1186/1743-8977-9-44.
Respirable crystalline silica (RCS) continues to pose a risk to human health worldwide. Its variable toxicity depends on inherent characteristics and external factors which influence surface chemistry. Significant population exposure to RCS occurs during volcanic eruptions, where ashfall may cover hundreds of square km and exposure may last years. Occupational exposure also occurs through mining of volcanic deposits. The primary source of RCS from volcanoes is through collapse and fragmentation of lava domes within which cristobalite is mass produced. After 30 years of research, it is still not clear if volcanic ash is a chronic respiratory health hazard. Toxicological assays have shown that cristobalite-rich ash is less toxic than expected. We investigate the reasons for this by determining the physicochemical/structural characteristics which may modify the pathogenicity of volcanic RCS. Four theories are considered: 1) the reactivity of particle surfaces is reduced due to co-substitutions of Al and Na for Si in the cristobalite structure; 2) particles consist of aggregates of cristobalite and other phases, restricting the surface area of cristobalite available for reactions in the lung; 3) the cristobalite surface is occluded by an annealed rim; 4) dissolution of other volcanic particles affects the surfaces of RCS in the lung.
The composition of volcanic cristobalite crystals was quantified by electron microprobe and differences in composition assessed by Welch's two sample t-test. Sections of dome-rock and ash particles were imaged by scanning and transmission electron microscopy, and elemental compositions of rims determined by energy dispersive X-ray spectroscopy.
Volcanic cristobalite contains up to 4 wt. % combined Al(2)O(3) and Na(2)O. Most cristobalite-bearing ash particles contain adhered materials such as feldspar and glass. No annealed rims were observed.
The composition of volcanic cristobalite particles gives insight into previously-unconsidered inherent characteristics of silica mineralogy which may affect toxicity. The structural features identified may also influence the hazard of other environmentally and occupationally produced silica dusts. Current exposure regulations do not take into account the characteristics that might render the silica surface less harmful. Further research would facilitate refinement of the existing simple, mass-based silica standard by taking into account composition, allowing higher standards to be set in industries where the silica surface is modified.
可吸入结晶二氧化硅(RCS)仍然对全球人类健康构成威胁。其变异性毒性取决于影响表面化学性质的固有特性和外部因素。在火山爆发期间,大量人群会接触到 RCS,火山灰可能覆盖数百平方公里,暴露时间可能长达数年。通过开采火山沉积物也会发生职业暴露。火山 RCS 的主要来源是通过崩塌和碎片形成的熔岩穹顶,其中大量生产方石英。经过 30 年的研究,火山灰是否是慢性呼吸道健康危害仍不清楚。毒理学试验表明,富含方石英的火山灰的毒性低于预期。我们通过确定可能改变火山 RCS 致病性的物理化学/结构特征来研究其原因。有四种理论被考虑:1)方石英结构中 Si 被 Al 和 Na 取代,导致颗粒表面的反应性降低;2)颗粒由方石英和其他相的聚集体组成,限制了肺中可用的方石英表面积进行反应;3)方石英表面被退火边缘封闭;4)其他火山颗粒的溶解会影响肺中 RCS 的表面。
通过电子探针定量分析了火山方石英晶体的组成,并通过 Welch 两样本 t 检验评估了组成差异。通过扫描和透射电子显微镜对穹顶岩和灰颗粒的截面进行成像,并通过能量色散 X 射线光谱法确定边缘的元素组成。
火山方石英中含有高达 4wt%的结合 Al2O3 和 Na2O。大多数含方石英的灰颗粒含有附着的物质,如长石和玻璃。未观察到退火边缘。
火山方石英颗粒的组成提供了对以前未考虑的二氧化硅矿物学固有特性的深入了解,这些特性可能会影响毒性。所确定的结构特征也可能影响其他环境和职业产生的二氧化硅粉尘的危害。目前的暴露法规没有考虑到可能使二氧化硅表面危害降低的特性。进一步的研究将促进在考虑组成的情况下对现有的简单、基于质量的二氧化硅标准进行细化,从而可以在二氧化硅表面被修饰的行业中设定更高的标准。