More than a quarter of workers tested at
an Ohio vermiculite manufacturing plant showed scarring of the chest
wall lining, UC researchers have found.
The researchers examined recent chest
X-rays of 236 people who worked at the Marysville plant, which until
1980 used vermiculite ore containing asbestos fibers.
Sixty-two of the workers (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, which was mined in Libby,
Mont. 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 asbestos exposure. This potentially increases the
risk for other asbestos-related lung changes, including scarring and
certain types of cancer, such as mesothelioma.
Preliminary results of the study were
presented in San Diego May 24 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 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.
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
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 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 still 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.