Meij R, Nagengast S, Te Winkel H
a KEMA , Arnhem , The Netherlands.
Inhal Toxicol. 2000 Jan;12 Suppl 3:109-16. doi: 10.1080/08958378.2000.11463236.
In spite of the presence of quartz, coal fly ash can be considered as a nuisance or inert dust. Respirable crystalline silica (e.g., quartz) is notorious for the induction of, for example, progressive massive fibrosis (PMF); besides, in 1997 the IARC stated that crystalline silica in the form of quartz or cristobalite from occupational sources is carcinogenic to humans. Quartz is present in both coal and residual ash. Ash originates from combustion of pulverised coal and, once removed from the flue gases by electrostatic precipitators (ESPs), it is called pulverized fuel ash (PFA). Thus, occupational exposure to PFA could also include exposure to silica. However, epidemiological studies did not show evidence of progressive massive fibrosis (PMF). In vitro tests demonstrated that PFA is less toxic than silica, and in vivo data of PFA did not support the importance of silica content for toxicity. Commissioned by the Dutch coal-fired power plants, KEMA has started a research project to determine the quartz content in coal and the corresponding PFA. It appears that on average 50% of the a-quartz in coal is found again in the total fraction of PFA (D50(ae) 31 µm, where Dsotae) is the aerodynamically mass median diameter), whereas 16% is found in an even finer fraction (D50(ae) 10 µm). The remaining part of the quartz is embedded in a glass phase. Scanning electron microscopy (SEM) with x-ray microanalyses (XMA) of cross-sections of 11,130 ash particles showed that quartz in PFA is present as unmelted sand particles. These quartz particles are angularly shaped. However, two types are to be distinguished: free coarse angular quartz particles (not respirable) and small angular quartz particles within the PFA particles. From the SEM/XMA results, it has to be concluded that the quartz in the respirable fraction is predominantly present within the original molten PFA particle. Since the effects of quartz are surface related, this elucidates the negative results of quartz-related effects of PFA in epidemiological, in vitro and in vivo studies. Besides, the amount of the total α-quartz in the respirable fraction of the ashes studied is less than 0.2%, so probably the Dutch occupational quartz standard of 0.075 mg m(-3) will not be exceeded.
尽管存在石英，但煤粉煤灰可被视为无害或惰性粉尘。可吸入性结晶二氧化硅（如石英）因可诱发例如进行性块状纤维化（PMF）而声名狼藉；此外，1997年国际癌症研究机构指出，职业来源的石英或方石英形式的结晶二氧化硅对人类具有致癌性。石英存在于煤和残余灰分中。灰分源自煤粉燃烧，一旦通过静电除尘器（ESP）从烟气中去除，就称为粉煤灰（PFA）。因此，职业接触PFA也可能包括接触二氧化硅。然而，流行病学研究并未显示进行性块状纤维化（PMF）的证据。体外试验表明，PFA的毒性低于二氧化硅，且PFA的体内数据不支持二氧化硅含量对毒性的重要性。受荷兰燃煤电厂委托，KEMA已启动一项研究项目，以确定煤和相应PFA中的石英含量。结果表明，煤中平均50%的α-石英在PFA的总部分中再次被发现（空气动力学质量中值直径D50(ae) 31 µm，其中Dsotae是空气动力学质量中值直径），而16%在更细的部分中被发现（D50(ae) 10 µm）。石英的其余部分嵌入玻璃相中。对11130个灰分颗粒的横截面进行扫描电子显微镜（SEM）和X射线微分析（XMA）显示，PFA中的石英以未熔化的砂粒形式存在。这些石英颗粒呈角状。然而，有两种类型需要区分：游离的粗角状石英颗粒（不可吸入）和PFA颗粒内的小角状石英颗粒。从SEM/XMA结果可以得出结论，可吸入部分中的石英主要存在于原始熔融的PFA颗粒内。由于石英的作用与表面有关，这解释了PFA在流行病学、体外和体内研究中与石英相关作用的阴性结果。此外，所研究灰分的可吸入部分中总α-石英的含量低于0.2%，因此可能不会超过荷兰职业石英标准0.075 mg m(-3)。
