1. Department of Environmental and Occupational Health Sciences, School of Public Health, University of Illinois Chicago, Chicago, Illinois;
2. Respiratory Health Division and
3. Department of Environmental and Occupational Health Services, National Jewish Health and University of Colorado, Denver, Colorado;
4. Department of Mining and Minerals Engineering, Virginia Tech, Blacksburg, Virginia;
5. U.S. Geological Survey, Denver, Colorado;
6. Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, West Virginia;
7. Department of Pathology, Upstate Medical University, State University of New York, Syracuse, New York;
8. Department of Pathology, University of Colorado, Denver, Colorado;
9. Department of Pathology and Laboratory Medicine, University of Calgary, Calgary, Alberta, Canada;
10. School of Public Health, University of the Witwatersrand, Johannesburg, South Africa;
11. Histopathology, Lancet Laboratories, Johannesburg, South Africa; and
12. Section of Pulmonary Medicine, West Virginia University, Morgantown, West Virginia