Workers Exposed To Libby Vermiculite Ore Have High Rate Of Chest Wall Abnormalities

Researchers examined recent chest X-rays of 236 people who worked at a plant in Marysville, Ohio, that until 1980 used vermiculite ore mined in Libby, Mont., that contained asbestos fibers.

Of the 236 workers tested, 62 (26.3 percent) showed pleural plaques, or scarring of the chest wall lining. The occurrence was as high as 44.1 percent in workers with the largest and heaviest exposure to the vermiculite ore. The percentage of workers with pleural plaques was 5.1 percent in those with the lowest levels of exposure.

Pleural plaques are usually considered markers of previous exposure to asbestos fibers. Because of the previous exposure to asbestos, there is a potential increased risk for other asbestos-related lung changes, including scar tissue within the lungs and certain types of cancer such as mesothelioma.

Preliminary results of the study were presented in San Diego May 24, 2005, at the annual International Conference of the American Thoracic Society.

"Our study shows that cumulative exposure to vermiculite from Libby is associated with a significant increase in pleural changes," said study leader James Lockey, MD, professor of occupational and pulmonary medicine at the University of Cincinnati College of Medicine.

"There is clearly a relationship with increasing exposure, but the pleural changes also were seen in the low-exposed workers," said co-author Amy Rohs, MD, a fellow in occupational and pulmonary medicine at University of Cincinnati.

About 0.2 percent of the general population with minimal history of exposure to respiratory hazards shows signs of pleural plaques, Dr. Lockey noted. "I was surprised at the significant increase in overall pleural changes in this working population from 2 percent in 1980 to 26 percent, based on these preliminary results," he added.

"The public health implications of these preliminary findings are important in view of the national distribution of the Libby vermiculite ore," the authors concluded.

Until 1990, more than 200 sites around the country received shipments of vermiculite from the Libby mine.

Vermiculite is a group of minerals with a flaky, mica-like structure. Vermiculite ore from Libby has been shown to contain high levels of asbestos, which could have become airborne and inhaled when used in manufacturing. Vermiculite is widely used in a variety of applications, including insulation, packing materials, construction materials and gardening products. The Libby mine closed in 1990 and vermiculite ore used now comes from other sources and is not known to contain asbestos.

The X-rays were taken during the past two years, and each was reviewed independently by three board-certified radiologists. Spirometry tests, which measure lung function, and health histories also were taken. Although these were not assessed for this study, they will be reported later when the complete study findings are reviewed and published.

The workers were among a group of 513 employees at the Ohio plant exposed to vermiculite and who took part in a 1980 study. Of these 513 workers, 433 (84 percent) are currently alive. That original study, published by Dr. Lockey in the June 1984 issue of American Review of Respiratory Disease, initially showed that exposure to vermiculite containing asbestos fibers could cause pleural plaques.

The current study was funded by the Agency for Toxic Substances and Disease Registry (ATSDR) of the Centers for Disease Control and Prevention (CDC). Additional information on ATSDR and Libby asbestos can be found at http://www.atsdr.cdc.gov/naer/index.html.

Co-authors of the study were Kari Dunning, PhD, Jerome Wiot, MD, Ralph Shipley, MD, Chris Meyer, MD, Tim Hilbert and Rakesh Shukla, PhD, of the University of Cincinnati and Vikas Kapil, DO, of the CDC/ATSDR.