SOT Spotlight: Q&A with Mike Ierardi
What is the title of your presentation?
Derivation of a Proposed Asbestiform Tremolite NOAEL for Lung Cancer
What was the scope of your research?
In our analysis, we derived a proposed range of “no-effect” cumulative exposure levels, or NOAELs, for asbestiform tremolite exposure and lung cancer using two distinct approaches. Similar analyses have previously been performed to derive an asbestiform tremolite NOAEL for mesothelioma (Finley et al. 2012), as well as chrysotile NOAELs for both mesothelioma and lung cancer (Pierce et al. 2008; 2016). Since asbestiform tremolite is occasionally found in some chrysotile and vermiculite deposits, we focused our NOAEL analysis on potential high-exposure occupational cohorts who worked mining or processing chrysotile from Quebec or vermiculite from Libby, Montana, as well as those residing around these areas. For approach 1, we evaluated lung cancer risk at stratified levels of cumulative exposure among these chrysotile- and vermiculite-exposed cohorts. For approach 2, we utilized published relative potency factors for Libby amphiboles (as a surrogate for asbestiform tremolite) and chrysotile (Berman and Crump, 2008; Hodgson and Darnton, 2000; Moolgavkar et al., 2010), and applied these potency factor ratios to a published chrysotile lung cancer NOAEL of 89 to 168 f/cc-years (Pierce et al., 2016).
What did you find?
We found that a reasonable approximation of the asbestiform tremolite NOAEL for lung cancer is in the range of 0.27 to <2.6 f/cc-years using approach 1, and 0.20 to 3.7 f/cc-years using approach 2. We ultimately concluded that, according to the currently available epidemiology studies of asbestiform tremolite-exposed cohorts, evidence exists for a cumulative asbestiform tremolite exposure below which lung cancer risk is not significantly elevated. The very similar results from the two separate, yet complementary, approaches used in our study support this conclusion.
What are the next steps/what other research is needed?
Our findings provide useful benchmark comparisons for quantitative asbestos risk assessments, and future investigators are encouraged to derive additional fiber type-specific NOAEL values as the underlying epidemiological data allow.