Low levels of Libby asbestos exposure linked to lung abnormalities

Thirty years after the Libby mine was shut down, abnormalities are still found on chest computed tomography (CT) scans and lung function tests in more than half of workers exposed to Libby amphibole asbestos (LAA). "[T]hese changes occur at substantially lower cumulative fiber exposure levels than those commonly associated with commercial asbestos," writes Dr James E. Lockey of University of Cincinnati and colleagues. The study was sponsored by the Agency for Toxic Substance and Disease Registry.

The researchers followed up 431 living workers, from an original group of 513 LAA-exposed workers first studied in 1980. The workers were exposed to a particularly hazardous form of asbestos from contaminated vermiculite that had been mined in Libby for decades.

Of 191 workers with available CT scans, 53 percent had asbestos-related changes of the tissue lining the lungs (pleura), while 13 percent had changes of the lung substance (parenchyma). Greater involvement on imaging scans was related to greater average reductions in lung function (forced vital capacity): up to 18 percent for those with extensive pleural and/or parenchymal changes.

The CT scan abnormalities were present even in workers with lower levels of estimated lifetime exposure to LAA -- about three to ten times below current standards for commercial asbestos exposure. The asbestos-related lung abnormalities "can be particularly relevant when potentially combined with other respiratory [diseases] that can occur over a person's lifetime that can impact lung function," Dr Lockey and coauthors conclude.