Localized Pleural Thickening: Smoking and Exposure to Libby Vermiculite [journal Article]
There is limited research on the combined effects of smoking and asbestos exposure on risk of localized pleural thickening (LPT). This analysis uses data from the Marysville cohort of workers occupationally exposed to Libby amphibole asbestos (LAA). Workers were interviewed to obtain work and health history (including ever/never smoking), including chest X rays. Cumulative exposure estimates were developed based on fiber measurements from the plant and work history. Benchmark concentration (BMC) methodology was used to evaluate the exposure-response relationship for exposure to LAA and a 10% increased risk of LPT, considering potential confounders and statistical model forms. There were 12 LPT cases among 118 workers in the selected study population. The mean exposure was 0.42 (SD=0.77) fibers/cc-year, and the prevalence smoking history was 75.0% among cases, and 51.9% among non-cases. When controlling for LAA exposure, smoking history was of borderline statistical significance (p value = 0.099), and its inclusion improved model fit, as measured by AIC. The BMC and corresponding lower limit (BMCL) were 0.36 and 0.13 fiber-yr/cc, overall. The BMCL for non-smokers was twice as high (0.26 fiber-yr/cc) as that for the full cohort, while the BMCL for smokers was about 1/3 that of the full cohort (0.04 fiber-yr/cc).