In the small town of Libby in north western Montana, prospectors in 1916 discovered an unusual mineral known as vermiculite that appeared to be resistant to fire after initial exposure to high heat.
The early owners of the mine called their product Zonolite, and for the next half century they dug it out of the Libby mountain and shipped it across the continent for use as insulation and in various commercial products.
Unfortunately, the mine and its product also contained asbestos, and by the 1980s, hundreds of the miners who worked at Zonolite mountain — and their family members — had sickened and died of asbestos-related diseases at rates 40 times higher than the U.S. as a whole.
Little was known outside of Libby about the cluster of diseases until 1999, when Seattle Post-Intelligencer reporter Andrew Schneider published a series of stories called “Uncivil Action: A Town Left to Die,” which began by saying “First, it killed some miners. Then it killed wives and children, slipping into their homes on the dusty clothing of hard-working men. Now the mine is closed, but in Libby, the killing goes on.”
Then in a 2004 book about the case, An Air that Kills: How the Asbestos Poisoning of Libby, Montana, Uncovered a National Scandal, Schneider and co-author David McCumber wrote, “The sickening of Libby was such a gradual thing. Like a person with asbestos-scarred lungs that are slowly losing their capacity, a town that is slowly dispatching its miners to the graveyard, slowly increasing its per-capita use of oxygen tanks, slowly increasing its quotient of widows with shortness of breath, does not immediately realize what is happening.”
The mine closed in 1990, and owners W.R. Grace has since faced hundreds of thousands of lawsuits for asbestos-related illness, most often cancer and asbestosis. (The company was acquitted in 2009 of knowingly harming the people of Libby and of covering up its knowledge of the health hazards from the mine.)
But now, a group of researchers from Idaho State University and the Centre for Environmental Health Sciences at the University of Montana are suggesting that a further health concern should be added to the list of woes faced by the Libby residents: autoimmune disease, including an as-yet undescribed autoimmune condition affecting the lungs.
Asbestos and the Immune System
It’s long been known that exposure to another silicate dust, crystalline silica, is associated with the development of autoimmunity, but this had not been recognized for asbestos.
The term asbestos refers to a group of mineral fibres that are classified as “serpentine” or “amphibole,” and most studies of occupational exposure have focused on the serpentine fibre chrysotile. In contrast, the Libby asbestos contained a variety of amphibole fibres, including winchite, richterite, and tremolite.
One of the Idaho researchers, Jean C. Pfau, PhD, explained that the various types of asbestos fibres appear to have quite different effects on the immune system.
“Exposure to the common chrysotile asbestos most often has been associated with cancer, possibly because it suppresses the immune response and the ability of the immune system to destroy the cancer,” she said.
“But the amphibole asbestos in Libby doesn’t seem to do that. Instead, it appears to activate the immune system leading to the production of autoantibodies,” she told MedPage Today.
Many different types of autoantibodies have been identified in both mouse and human studies, including antinuclear antibodies and rheumatoid factor, along with increases in serum immunoglobulins and the deposition of immune complexes typical of lupus.
The Montana Study
In the early 2000s, the CDC conducted an extensive screening program in Libby in an attempt to quantify the extent of the health disaster, questioning more than 7,000 residents of the town about potential exposures. Among their findings was the observation that 494 individuals reported ever having been diagnosed with lupus, rheumatoid arthritis, or systemic sclerosis. This represented 6.7% of the population, which far exceeded the expected prevalence of less than 1% for these conditions, they noted.
To examine this more closely, Pfau and colleagues collected serum samples from local residents, comparing their autoantibody profiles with matched controls from Missoula, an area of Montana where no asbestos had been mined.
In a study published in Environmental Health Perspectives, they found that, among 50 serum samples from Libby residents, the frequency of ANAs was 28.6% higher than in the Missoula samples (P=0.006). They also reported that the mean fluorescence intensity of the ANAs was significantly higher (2.34 versus 1.76, P=0.02).
The researchers also found that 24% of the Libby samples contained antibodies to extractable nuclear proteins such as Sm, SS-a, and SS-b, which are commonly found in patients with systemic lupus erythematosus. Only 4% of the Missoula samples contained these antibodies.
The odds ratios among Libby residents ages 65 and older who had worked at the mine were 2.14 (95% CI 0.90-5.10) for systemic autoimmunity and 3.23 (95% CI 1.31-7.96) for rheumatoid arthritis specifically.
Moreover, while the number of cases of lupus (30) was too small to calculate an odds ratio, the researchers estimated that individuals who had had multiple possible exposures, such as through their job, recreation, and using vermiculite in gardening, had a more than fourfold risk (OR 4.45, 95% CI 1.24-16).
Now, however, Pfau’s group is focusing on a specific subgroup of patients in Libby who have developed an unusual very severe and progressive pulmonary illness. Many succumb to infections.
“These patients are in terrible pain and lose their lung function because their lungs aren’t elastic enough for them to breathe in and out, as though there’s a wrapping of scar tissue around their lungs,” she said.
This appears similar to what they found following amphibole exposure in their earlier mouse studies: the production of autoantibodies was followed by an increase in scarring in the connective tissues surrounding the lungs.
“We are proposing that this is a novel autoimmune disease, and we’re now working on the data that might actually show cause and effect, rather than just an association,” she said.
An Enduring Legacy
Records show that 9,780,000,000 pounds (italics mine) of vermiculite ore was mined from 1960 to 1990 and shipped to 563 different addresses in the United States and another 187 in six Canadian provinces.
It was used as insulation in millions of homes, and among the many other construction projects that utilized Zonolite for insulation was the World Trade Centre. When the towers fell on 9/11, the airborne debris that covered lower Manhattan and blew across the region contained an unknown quantity of fibres that originated on that mountainside in Montana.
Libby isn’t the only source of potential amphibole asbestos contamination. Recently, another group of mineral experts reported high levels in samples of soil and airborne dust obtained in the vicinity of Las Vegas.
“That heightens the public health problem, or pending crisis if you will,” Pfau said. “A lot of people think asbestos is an outdated occupational exposure that’s not occurring anymore. But that’s not true. There are a lot of exposures happening right now, and we want physicians to be aware and watching for this,” she said.
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