Vermiculite Linked To Lung Damage, Even At Legal Exposure Levels
March 14th, 2008 | by admin |
Workers at a plant that processed vermiculite with asbestos-like fibershave scarring and thickening of the membrane that lines the chestwalls, 25 years after the plant stopped using the material. In a studypublished in the American Journal of Respiratory and CriticalCare Medicine, researchers show similar results even forworkers who were exposed to the material - from a mine in Libby,Montana - at or below current legal levels.
Vermiculite is a natural mineral that can expand to about 20 times itsoriginal size with the application of heat. The mineral is used inseveral consumer products, such as loose-fill home insulation, soilconditioner or additive, and packaging materials. After researchersfound bloody pleural effusions (blood in the fluid-filled spacesurrounding the lungs) among workers who handled vermiculite in the1970s, it was suspected that the “Libby vermiculite” caused lungdamage. One of the largest and oldest vermiculite mines in the UnitedStates, the Libby mine produced about 80 percent of the vermiculiteused around the world.
The study, conducted by James Lockey, M.D. (University of Cincinnati)and colleagues, is a follow-up to a 1980 investigation of 513 workersat a plant that processed Libby vermiculite. In 1980, researchers foundpleural changes or interstitial fibrosis in 2.2% of the workers. Thefollow-up study reveals that 28.7% of the still-living members of theoriginal cohort had pleural changes and 2.9% had interstitial fibrosis.
“I expected to see a higher rate of x-ray changes, but was surprised atthe percentage,” writes Lockey. “We found that even low levels ofexposure to asbestos-like fibers can cause thickening of the membranethat lines the chest wall.”
In the follow-up study, 280 of the 431 still-living workers from theoriginal group participated. They were interviewed about lung healthand work history, providing data about particular exposure levels andthe numbers of years they worked. Participants were also given chestx-rays, allowing professional radiologists to identify pleural plaques,thickening, and interstitial changes.
Results of the research suggest that there exists a significant trendof increasing pleural changes as exposure levels increase. Amongworkers who had the highest exposure levels, there was about a 6 to 16times increase in risk of pleural changes compared to minimally-exposedworkers. In addition, the pleural changes were significant at levels ofexposure that current law permits.
An accompanying editorial, written by Gregory Wagner, M.D.(National Institute for Occupational Safety and Health), mentions that,”a significant number of workers exposed at the current limit wouldexperience pleural abnormalities.” However, legal exposure limits tohazardous materials, as specified by government regulations, do notapply to all types of fibers that have similar and predictablebiological effects. Often, they only apply to specific fibers.
Lockey adds, “When humans are exposed to any mineral fibers that arelong, thin and durable in human tissue and can reach the pleuralmembrane, these fibers can cause health problems.” Currently, there aresix types of asbestos that are regulated, “but other existing types offibers that share similar characteristics are not.” Lockey’s researchemphasizes the need to further analyze how occupational exposureaffects health.
“The initial Lockey investigation found a relatively modest prevalenceof pleural abnormalities,” writes Dr. Wagner. This follow-up “foundover 10 times that level, despite the fact that contaminatedvermiculite had been removed from the production process by 1980.”
As a caution to consumers, Dr. Lockey suggests that home improvementsthat require contact with vermiculite insulation should be done byprofessionals; however, consumers face minimal risk from mostproducts that contain or contained vermiculite from the Libby mine.
Low-Level Fiber-induced Radiographic Changes Caused byLibby Vermiculite: A 25-Year Follow-up Study
Amy M. Rohs, James E. Lockey, Kari K. Dunning, Rakesh Shukla, HuihaoFan, Tim Hilbert, Eric Borton, Jerome Wiot, Cristopher Meyer, Ralph T.Shipley, Grace K. LeMasters, and Vikas Kapi
American Journal of Respiratory and Critical Care Medicine(2008). 177:630-637.
doi:10.1164/rccm.200706-841OC
ClickHere to View Abstract
Written by: Peter M Crosta
Copyright: Medical News Today
Stumble it!
