Butnor Kelly J, Sporn Thomas A, Roggli Victor L
University of Vermont Medical Center, Department of Pathology, Burlington, VT 05405, USA.
Ann Occup Hyg. 2003 Jun;47(4):325-30. doi: 10.1093/annhyg/meg048.
A large number of workers in the USA are exposed to chrysotile asbestos through brake repair, yet only a few cases of malignant mesothelioma (MM) have been described in this population. Epidemiologic and industrial hygiene studies have failed to demonstrate an increased risk of MM in brake workers. We present our experience of MM in individuals whose only known asbestos exposure was to brake dust and correlate these findings with lung asbestos fiber burdens.
Consultation files of one of the authors were reviewed for cases of MM in which brake dust was the only known asbestos exposure. Lung fiber analyses were performed using scanning electron microscopy (SEM) in all cases for which formalin-fixed or paraffin-embedded lung tissue was available.
Ten cases of MM in brake dust-exposed individuals were males aged 51-73 yr. Nine cases arose in the pleura and one in the peritoneum. Although the median lung asbestos body count (19 AB/g) is at our upper limit of normal (range 0-20 AB/g), half of the cases had levels within our normal range. In every case with elevated asbestos fiber levels by SEM, excess commercial amphibole fibers were also detected. Elevated levels of chrysotile and non-commercial amphibole fibers were detected only in cases that also had increased commercial amphibole fibers.
Brake dust contains exceedingly low levels of respirable chrysotile, much of which consists of short fibers subject to rapid pulmonary clearance. Elevated lung levels of commercial amphiboles in some brake workers suggest that unrecognized exposure to these fibers plays a critical role in the development of MM.
在美国，大量工人通过刹车维修接触温石棉，但该人群中仅报告了少数恶性间皮瘤（MM）病例。流行病学和工业卫生研究未能证明刹车工人患MM的风险增加。我们介绍了仅已知石棉暴露源为刹车粉尘的个体患MM的经验，并将这些发现与肺部石棉纤维负荷相关联。
查阅其中一位作者的会诊档案，寻找仅已知石棉暴露源为刹车粉尘的MM病例。对于所有有福尔马林固定或石蜡包埋肺组织的病例，使用扫描电子显微镜（SEM）进行肺纤维分析。
10例暴露于刹车粉尘的MM患者均为男性，年龄在51 - 73岁之间。9例发生在胸膜，1例发生在腹膜。尽管肺部石棉小体计数中位数（19个/克）处于我们的正常上限（范围为0 - 20个/克），但一半的病例处于我们的正常范围内。在每例经SEM检测石棉纤维水平升高的病例中，还检测到了过量的商业用闪石纤维。仅在同时伴有商业用闪石纤维增加的病例中检测到温石棉和非商业用闪石纤维水平升高。
刹车粉尘中可吸入温石棉含量极低，其中大部分为短纤维，可迅速从肺部清除。一些刹车工人肺部商业用闪石水平升高表明，未被认识到的这些纤维暴露在MM的发生中起关键作用。
