In 1980, researchers studied 513 individuals who worked in a plant processing vermiculite that originated from a mine in Libby, Mont. The material these workers handled would meet current legal levels of exposure. A recent follow-up study examined 280 of the 431 surviving workers from the original group and interviewed them about their lung health, work history, exposure levels and the number of years worked. The participants were given chest x-rays and assessed by professional radiologists.
The research shows that even though the plant has not used the asbestos-like material in 25 years, many of these workers are affected by lung damage. Lead researcher Dr. James Lockey of the University of Cincinnati, who also was the principle investigator of the 1980 study, found that even low levels of exposure to the asbestos-like fibers could cause thickening of the chest wall membrane.
“When humans are exposed to any mineral fibers that are long, thin and durable in human tissue and can reach the pleural membrane, these fibers can cause health problems,” Lockey said. “Six types of asbestos are currently regulated, but other existing types of fibers that share similar characteristics are not.”
Dr. Gregory Wagner of the National Institute for Occupational Safety and Health (NIOSH) wrote that while the initial study found a modest prevalence of abnormalities, the current study “found over 10 times that level, despite the fact that contaminated vermiculite had been removed from the production process by 1980.”
Researchers also found a trend of increasing changes with increased exposure. Workers with the highest exposure levels, for example, had an average of six to 16 times the risk of pleural changes when compared to those who were minimally exposed. Changes were significant even at levels in compliance with legal regulations, suggesting the health implications of occupational exposure should be closely examined.
The “Libby vermiculite” was first suspected of causing lung damage in the late 1970s. Vermiculate, a mineral that expands to 20 times its size when heated rapidly, is used in gardening products, loose-fill home insulation and other consumer application. At one time, the Libby mine produced up to 80 percent of the vermiculite used around the world.
According to Lockey, consumers face minimal risk from most products that contain the Libby vermiculite, but he added that home improvements involving contact with vermiculite insulation be handled by professionals.
The study’s findings appear in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.