An updated evaluation of reported no-observed adverse effect levels for chrysotile asbestos for lung cancer and mesothelioma

Abstract

Although consumption of chrysotile asbestos has decreased since the 1970s, the latency period of asbestos-related cancers is thought to be at least 20–30 years, and therefore the potential health risks associated with historical exposures is still actively researched. This analysis represents an update to a previous paper in which we evaluated the exposure–response relationships for lung cancer and mesothelioma in chrysotile-exposed cohorts. Here, we review several recently published studies as well as updated information from previous studies. For each of the 14 studies considered, we identified the “no-observed adverse effect level” (NOAEL) for lung cancer and/or mesothelioma. NOAEL values for lung cancer ranged from 1.1 to <20 f/cc-years to 1600–3200 f/cc-years, and for mesothelioma ranged from 100–400 f/cc-years to 800–1599 f/cc-years. The range of “best estimate” NOAELs was estimated to be 89–168 f/cc-years for lung cancer and 208–415 f/cc-years for mesothelioma. None of the six cohorts of cement or friction product manufacturing workers exhibited an increased lung cancer risk at any exposure level, while all of the five studies of textile workers reported an increased risk at one or more exposure levels. This is likely because friction and cement workers were exposed to much shorter chrysotile fibers. Of the seven cases of peritoneal mesothelioma reported in the included studies, none were observed in the analyses of cement or friction product manufacturing workers in the absence of crocidolite exposure. These findings will help characterize potential worker and consumer health risks associated with historical and current chrysotile exposures.

Keywords:

• Asbestos
• chrysotile
• lung cancer
• mesothelioma
• NOAEL

Acknowledgements

The authors gratefully acknowledge the insightful reviews provided by four individuals selected by the Editor and anonymous to the authors. The comments and suggestions were valuable in revising the paper.

Declaration of interest

All the authors are employed by Cardno ChemRisk, a consulting firm that provides scientific advice to the government, corporations, law firms and various scientific/professional organizations. Cardno ChemRisk has been engaged by numerous companies involved in asbestos litigation, and two of the authors (Drs Pierce and Finley) have served and may serve again as experts in asbestos litigation. However, the time invested by the authors to write this paper was provided by their employer, and no external funding was received for the study, the research supporting the analysis, nor the time needed to prepare the article. Furthermore, the work product including the conclusions drawn are exclusively those of the authors, and have not been influenced by anyone other than the authors. Aside from the authors, no one, including clients of Cardno ChemRisk, has reviewed, commented on or revised this paper prior to its submission.

Supplemental material

Supplemental material for this article is available online here.

• Supplemental Table 1: Risk estimates for lung cancer in chrysotile cohorts stratified by exposure group.

• Supplemental Table 2: Risk estimates for mesothelioma in chrysotile cohorts stratified by exposure group.

Notes

1. In analyzing the same exposure data, McDonald et al. (1983a) reported a particle to fiber ratio that ranged from 1.3 to 10, with an average of roughly 6 f/cc per mppcf.