Asbestos Exposure Results

Demographic and exposure characteristics of study subjects by selected causes of death:

Among the 752 white men with known cause of death, 13.2% died from lung cancer, 2.0% from mesothelioma, and 5.3% with asbestosis. The average age at hire among study subjects was 29.7 years (range, 15.4–69.8 years).

The mean duration of employment for all 1,672 study subjects was 4.0 years and ranged from 1 day to 43.1 years. In contrast, the mean duration of employment was 7.1 years among workers who died with cancer of the lung or bronchus, 10.8 years among those with mesothelioma, and 14.6 years among those with a diagnosis of asbestosis listed on their death certificates.

Similarly, median cumulative exposure was estimated at 8.7 fibers/cc-years among all workers and 21.0 fibers/cc-years among those dying through 2001, but 28.2, 145.1, and 228.4 fibers/cc-years among those dying with lung cancer, mesothelioma, or asbestosis, respectively. On average, 34.8 years passed between hire and the study end date (or death); the maximum time since hire was 66.8 years.

Allowing for a 15-year exposure lag, asbestos-exposed Libby vermiculite workers were 24% more likely to have died by the end of 2001 compared with white men of the same 5-year age group in the U.S. population (SMR = 1.2; 95% CI, 1.1–1.3), and were 37% more likely to have died from cancer (SMR = 1.4; 95% CI, 1.2–1.6).

Libby workers also experienced significant excess mortality from cancer of the trachea, bronchus, and lung (SMR = 1.7; 95% CI, 1.4–2.1) and nonmalignant respiratory disease (SMR = 2.4; 95% CI, 2.0–2.9) after allowing for a 15-year exposure lag.