Chrysotile: New Exposure Indices and Cancer Epidemiology

描述：石棉被列为一种明确的人类致癌物，在现行的美国法规下，所有形式的石棉都被视为同等危险。温石棉是石棉最常用的形式，虽然美国限制使用温石棉，但由于大量的就地纤维和发展中国家的使用量正在增加，维修人员和建筑物居住者继续暴露在石棉中。尽管积累了大量的科学证据，但关于石棉，特别是温石棉的致癌性，仍有许多问题尚未解决。一些研究人员认为，与接触温石棉相关的癌症风险要比接触角孔形式的石棉低得多。在接触温石棉的工人中，纺织工人患肺癌的风险极高，而矿工和磨坊主患肺癌的风险要低得多，这两者之间存在着无法解释的对比。这些争议很难解决，因为只有少数独立的研究有足够的暴露-反应信息。为了解决有关温石棉的开放性问题，我们建议对北卡罗来纳州四家石棉纺织厂的5818名工人进行历史队列研究，这些工厂有石棉暴露的大量数据，但从未对其癌症发生率进行过研究。本流行病学研究的主要目标是：1)使用基于纤维浓度的既定指标和使用透射电子显微镜来解释纤维分布、尺寸和表面积的新指标来估计纺织工人对温石棉的暴露；2)在控制潜在的混杂职业暴露的情况下，描述温石棉累积暴露与肺癌死亡率之间的定量关系；3)根据石棉暴露的新指标，包括纤维尺寸分布、纤维尺寸和纤维表面积的测量，评估肺癌的风险。对这一新人群进行良好的流行病学调查将提供急需的信息，以帮助回答有关先前研究的普遍性和温石棉的相对危险性的问题。此外，使用更充分地考虑石棉纤维长度和宽度双变量分布的暴露指数进行肺癌道德研究，将为所有形式的石棉以及人造矿物纤维的风险评估提供新的数据。

DESCRIPTION: Asbestos is classified as a definite human carcinogen, with all forms treated as equally hazardous under current US regulations. Chrysotile is the most commonly used form of asbestos and, while use of chrysotile is restricted in the US, maintenance personnel and building occupants continue to be exposed due to the vast quantities of in-place fiber and use in developing countries is increasing. Despite the accumulated scientific evidence, a number of questions remain unresolved concerning the carcinogencity of asbestos in general and chrysotile in particular. Some researchers argue that the cancer risk associated with exposure to chrysotile is much lower that that for amphibole forms of asbestos. Among workers exposed to chrysotile, an unexplained contrast also exists between the extremely high risk of lung cancer among textile workers and the much lower risk among miners and millers. These controversies are difficult to resolve because only a handful of independent studies have adequate exposure-response information. To address open questions about chrysotile, we propose a historical cohort study of 5818 workers at four North Carolina asbestos textile plants that have extensive data on asbestos exposures but where cancer occurrence has never been studies. The principal goals of this epidemiology study are: 1) To estimate textile workers' exposures to chrysotile asbestos using both established indicators based on fiber concentration and new indicators, which use transmission electron microscopy to account for fiber distribution, dimensions, and surface area; 2) To characterize the quantitative relationship between cumulative exposure to chrysotile and lung cancer mortality while controlling for potentially confounding occupational exposures, and 3) To also evaluate the risk of lung cancer with respect to new indicators of asbestos exposure, including measures of fiber size distribution, fiber dimensions, and fiber surface area. A well-conducted epidemiologic investigations of this new population would provide information badly needed to help answer questions concerning the generalizability of previous study, and about the relative hazardousness if chrysotile. Furthermore, research on lung cancer morality using exposure indices that account more fully for the bivariate distribution of asbestos fiber length and width would provide new data relevant to risk assessments for all forms of asbestos as well as man-made mineral fibers.