Wanting to learn as much as possible about present and future health risks to its employees, Grace awarded a research grant to McGill University in Canada in 1983 to conduct two health studies. Both studies, under the direction of Dr. J. Corbett McDonald, assessed the health risks associated with exposure to tremolite fibers in a mining environment.
- One study examined deaths that had occurred in a specific group of
current and former employees.
- The second study was an x-ray survey of a separate group of present and past Libby employees.
Dr. McDonald's research team had extensive experience conducting occupational health studies, specifically in the area of dust-related disease. Although Libby employees had been aware of the potential health risks associated with exposure to tremolite asbestos fibers, the McGill studies were undertaken to better understand those risks. The studies confirmed that Libby employees worked in an environment where the risk had been increasingly reduced in the prior 10 years.
The McGill Mortality Study
The first McGill study included 406 men employed before 1963 who had worked at least one year in Libby mining operations. The whereabouts of each individual as of July 1, 1983 was determined. There were 241 people living and 165 who had passed away.
| Causes of Death | |
| 43 | cancer |
| 21 | non-malignant lung disease |
| 65 | heart and stroke |
| 36 | other causes |
When compared to the expected death rate for U.S. white males in general, the figures showed an increase in the number of deaths in the Libby study group by 24 from all causes.
Conclusions: The study concluded that the increased number of deaths was directly related to lung cancer, mesothelioma (a rare cancer of the chest and abdominal cavity linings), non-malignant respiratory disease and non-work related accidents. Death certificates and employee work histories suggested the increased number of deaths was almost entirely related to exposure to tremolite fibers during the 1940s, ‘50s and ‘60s, when the levels of fiber exposure were exceedingly higher (more than 1,000 times) than those of the Libby environment at the time of the study. There was no evidence of excess deaths from cancer of non-respiratory sites, such as stomach or intestinal cancer. While it could not be measured, it was believed that the cigarette smoking history of the Libby work population significantly contributed to the number of deaths from lung cancer.
The McGill study estimated that for every fiber year of exposure (meaning exposure to the equivalent of one fiber per cubic centimeter of air for a year's time), a Libby employee's risk of lung cancer was increased by 1%. In other words, at the exposure level of 0.1 f/cc in the Libby working environment at the time of the study, and assuming employment for 50 years, one could estimate the occurrence of about one-half a lung cancer case above that experienced throughout the U.S. Discontinuing cigarette smoking by all employees at Libby could do much to reduce the risk of lung cancer to levels below the national average.
The McGill X-ray Survey
The x-ray survey conducted by McGill University included a study group of 300 people in three categories.
- 164 men and 9 women employed at Libby as of July 1, 1983
- 80 former employees, living within 200 miles of the mine
- 47 local men without any known dust exposure who attended the
hospital for routine chest x-rays. (Control group for the x-ray
reading process.)
The study estimated that for every 100-fiber years of exposure, a Libby employee at retirement age had a potential 5-10% increased risk of developing lung opacities. At an exposure level of 0.1 f/cc-the level at the time of the study -- if an employee were hired then and worked 50 years in the mine, no detectable changes of lung tissues other than those related to aging, should have been evident on the employee's x-rays.
In 1985, the preliminary findings of both McGill University studies were presented to current employees and those former employees who had participated in the studies.
The NIOSH Studies
The preliminary findings of two similar studies by NIOSH in 1982 indicated lower levels of risk than those of the two McGill studies. The differences in the results of the studies were primarily due to NIOSH's use of higher estimated historical dust exposure levels for employees than those used by the McGill group.