Aeolus, Inc., Albany, California, USA.
Crit Rev Toxicol. 2010;40(2):151-88. doi: 10.3109/10408440903349137.
Results of a meta-analysis indicate that the variation in potency factors observed across published epidemiology studies can be substantially reconciled (especially for mesothelioma) by considering the effects of fiber size and mineral type, but that better characterization of historical exposures is needed before improved exposure metrics potentially capable of fully reconciling the disparate potency factors can be evaluated. Therefore, an approach for better characterizing historical exposures, the Modified Elutriator Method (MEM), was evaluated to determine the degree that dusts elutriated using this method adequately mimic dusts generated by processing in a factory. To evaluate this approach, elutriated dusts from Grade 3 milled fiber (the predominant feedstock used at a South Carolina [SC] textile factory) were compared to factory dust collected at the same facility. Elutriated dusts from chrysotile ore were also compared to dusts collected in Quebec mines and mills. Results indicate that despite the substantial variation within each sample set, elutriated dusts from Grade 3 fiber compare favorably to textile dusts and elutriated ore dusts compare to dusts from mines and mills. Given this performance, the MEM was also applied to address the disparity in lung cancer mortality per unit of exposure observed, respectively, among chrysotile miners/millers in Quebec and SC textile workers. Thus, dusts generated by elutriation of stockpiled chrysotile ore (representing mine exposures) and Grade 3 milled fiber (representing textile exposures) were compared. Results indicate that dusts from each sample differ from one another. Despite such variation, however, the dusts are distinct and fibers in Grade 3 dusts are significantly longer than fibers in ore dusts. Moreover, phase-contrast microscopy (PCM) structures in Grade 3 dusts are 100% asbestos and counts of PCM-sized structures are identical, whether viewed by PCM or transmission electron microscope (TEM). In contrast, a third of PCM structures in ore dusts are not asbestos and only a third that are counted by PCM are also counted by TEM. These distinctions also mirror the characteristics of the bulk materials themselves. Perhaps most important, when the differences in size distributions and PCM/TEM distinctions in these dusts are combined, the combined difference is sufficient to completely explain the difference in exposure/response observed between the textile worker and miner/miller cohorts. Importantly, however, evidence that such an explanation is valid can only be derived from a meta-analysis (risk assessment) covering a diverse range of epidemiology study environments, which is beyond the scope of the current study. The above findings suggest that elutriator-generated dusts mimic factory dusts with sufficient reliability to support comparisons between historical exposures experienced by the various cohorts studied by epidemiologists. A simulation was also conducted to evaluate the relative degree that the characteristics of dust are driven by the properties of the bulk material processed versus the nature of the mechanical forces applied. That results indicate it is the properties of bulk materials reinforces the theoretical basis justifying use of the elutriator to reconstruct historical exposures. Thus, the elutriator may be a valuable tool for reconstructing historical exposures suitable for supporting continued refinements of the risk models being developed to predict asbestos-related cancer risk.
一项荟萃分析的结果表明，通过考虑纤维尺寸和矿物类型的影响，可以在很大程度上协调已发表的流行病学研究中观察到的效力因素的变化（尤其是间皮瘤），但在评估可能完全协调不同效力因素的改进暴露指标之前，需要更好地描述历史暴露情况。因此，评估了一种更好地描述历史暴露情况的方法，即改良淘析器法（MEM），以确定使用该方法淘析的粉尘是否充分模拟了在工厂加工过程中产生的粉尘。为了评估该方法，从 Grade 3 磨碎纤维（南卡罗来纳州[SC]纺织厂使用的主要原料）中淘析的粉尘与同一设施收集的工厂粉尘进行了比较。还比较了温石棉矿石淘析的粉尘与魁北克矿山和工厂收集的粉尘。结果表明，尽管每个样本组内存在很大差异，但 Grade 3 纤维的淘析粉尘与纺织粉尘相比表现良好，矿石粉尘的淘析粉尘与矿山和工厂的粉尘相比也表现良好。鉴于这种性能，MEM 还被应用于解决温石棉矿工/加工厂工人和 SC 纺织工人分别观察到的单位暴露肺癌死亡率差异的问题。因此，对从储存的温石棉矿石淘析产生的粉尘（代表矿山暴露）和 Grade 3 磨碎纤维（代表纺织暴露）进行了比较。结果表明，每个样本之间的粉尘存在差异。尽管存在这种差异，但粉尘是不同的，Grade 3 粉尘中的纤维明显长于矿石粉尘中的纤维。此外，Grade 3 粉尘中的相衬显微镜（PCM）结构 100%为石棉，并且无论通过 PCM 还是透射电子显微镜（TEM）进行计数，PCM 大小结构的计数都是相同的。相比之下，矿石粉尘中的三分之一的 PCM 结构不是石棉，并且仅三分之一的 PCM 计数也被 TEM 计数。这些区别也反映了散装材料本身的特点。也许最重要的是，当这些粉尘的尺寸分布差异和 PCM/TEM 区别结合在一起时，总的差异足以完全解释纺织工人和矿工/加工厂工人队列之间观察到的暴露/反应差异。然而，重要的是，这种解释是否有效的证据只能从涵盖广泛的流行病学研究环境的荟萃分析（风险评估）中得出，这超出了当前研究的范围。上述发现表明，淘析器产生的粉尘与工厂粉尘具有足够的可靠性，可以支持流行病学家研究的不同队列之间的历史暴露情况的比较。还进行了模拟，以评估粉尘特性受加工散装材料的性质与机械力性质的影响的相对程度。结果表明，正是散装材料的性质增强了使用淘析器重建历史暴露情况的理论依据。因此，淘析器可能是一种用于重建历史暴露情况的有价值的工具，适用于支持正在开发的预测石棉相关癌症风险的风险模型的持续改进。
