Asbestos standards: Impact of currently uncounted chrysotile asbestos fibers on lifetime lung cancer risk.

Background: Current regulations require that asbestos fibers are collected and examined using a light microscope. This method fails to enumerate fibers that are too short or thin to reliably count using a light microscope under normal conditions.

Methods: A cohort of 3054 workers employed at an asbestos textile plant was followed to ascertain causes of death. Exposure was almost entirely chrysotile. Fiber counts were quantified using light microscopy and electron microscopy. The g-formula was used to estimate impacts on lung cancer of policies defined in terms of fiber counts quantified using light and electron microscopy.

Results: Given exposure at the current standard, the estimated lung cancer risk was 7.33%, comparable to the risk expected under a standard of 1 fiber/mL counted using electron microscopy (7.30%). The lifetime risk of lung cancer under a standard of 0.1 fiber/mL counted by electron microscopy was estimated to be 7.10%.

Conclusions: We identify policies defined in terms of electron microscopy-based asbestos exposure metrics that yield comparable, or lower, lung cancer mortality than that expected under the current standard.