Microscopic images of hazardous asbestos-like fibers found in rock formations in Southeastern Montana. Credit: Sources: USGS, MDoT & EPA.

Recent research is focusing new attention on an asbestos-like mineral, blamed for staggering rates of a deadly cancer in Turkey, that also is found in the rocks and soil of 13 Western states, including multiple sites in Montana.

The U.S. Geological Survey has identified 95 sites where the mineral, erionite, exists. And a recent hazard assessment at one of the sites, in the Custer National Forest, found that some Forest Service workers are being exposed to erionite particles in airborne dust as they carry out routine maintenance chores.

The air tests were conducted in the Sioux district of the forest, which straddles the border between far southeastern Montana and the northwest corner of South Dakota. The report — by the National Institute for Occupational Safety and Health, or NIOSH, part of the U.S. Centers for Disease Control and Prevention — reached no conclusions about the level of risk. But it advised steps to reduce the risk of breathing dangerous fibers, such as avoiding use of gravel containing erionite and wetting soil when doing work that raises clouds of dust.

Campground near The Castles, a massive rock formation with national landmark status in the Sioux District of the Custer National Forest in South Dakota (photo courtesy of the National Institute for Occupational Safety and Health).

Catherine Beaucham, a NIOSH industrial hygienist who led the study, said in an interview that she doesn’t know what the risk is to the health of the workers. “What I’m comfortable saying is they need to take proper precautions to reduce exposure,” she said.

Erionite was described in a 2008 scientific report as “almost certainly the most toxic naturally occurring fibrous mineral known.” In the Cappadocia region of central Turkey, an erionite-rich area where stone containing the mineral was used to build homes, researchers found extremely high incidence of mesothelioma, a cancer of the lining of the lung or abdomen that is extremely rare in the U.S. In some of the Turkish villages rates of mesothelioma were off the charts—responsible for 40 percent to 50 percent of all deaths. In the U.S., where most mesothelioma victims are former asbestos workers, there are about 3,200 cases reported annually.

Concern about chance exposure to erionite followed the disclosure in 2005 that, for years, erionite-rich gravel mined in western North Dakota had been spread on parking lots, at recreation sites and on hundreds of miles of unpaved roads, including school bus routes. As reported by FairWarning, air tests along gravel roadways and in vehicles, including inside school buses, revealed erionite levels similar to those in some stricken Turkish villages.

In North Dakota and the rest of the U.S., there have been no proven cases of mesothelioma stemming from erionite exposure. But experts say that is less than reassuring, because mesothelioma often develops 30 years or more after initial exposure, and when identified is automatically assumed to have been caused by occupational exposure to asbestos. The expansion of housing, roads and recreation in the arid expanses of the West has heightened concern about people breathing harmful dust from fibrous minerals.

Erionite, a naturally occurring asbestos-like mineral, has been found in rocks and soil at 95 locations in the West. Map adapted from “Geologic occurrences of erionite in the United States: an emerging national public health concern for respiratory disease”; Environmental Geochemistry and Health, August 2013.

Researchers in Mexico last year reported an unusual cluster of lung cancer and mesothelioma in the village of Tierra Blanca de Abajo in Central Mexico, attributing it to erionite in native rocks and soil.

Erionite is but one of about 400 naturally occurring fibrous minerals, most of them little studied. They are unregulated with the exception of asbestos, which actually is a commercial name for six regulated minerals that were heavily used to make insulating materials, floor and ceiling tiles, automotive brakes and many other products. When asbestos material is worn or broken, it can release microscopic fibers into the air. Over decades, hundreds of thousands of shipyard workers and others exposed on the job have been stricken with terminal illnesses such as asbestosis, lung cancer and mesothelioma, from breathing the brittle, lung-scarring fibers.

Health authorities have noted key physical similarities between some of the unregulated minerals, including erionite, and asbestos. Minerals that, when disturbed, can release microscopic particles that are longer than they are wide, and that don’t easily dissolve in the lung, “should be assumed [to be] capable of causing asbestos-related diseases,” said Christopher P. Weis, a toxicologist and senior advisor at the National Institute of Environmental Health Sciences. “It really doesn’t matter what they’re called.”

Chronic exposure to three fibrous minerals has taken a tragic toll on miners and residents of the town of Libby, Mont. The minerals were contaminants of vermiculite ore from a large mine that operated near the town from about 1920 to 1990. High rates of asbestos-related illnesses and deaths lingered long after closure of the mine. Along with mine workers, residents were exposed through use of the tainted vermiculite as home insulation, at recreation sites and in gardening projects around the town.

In 2014, a major highway project in southern Nevada was delayed for several months after University of Nevada geologists Brenda Buck and Rod Metcalf documented the presence of actinolite asbestos in rocks and soil in the construction area around Boulder City, about 30 miles southeast of Las Vegas. Tests ordered by transportation officials confirmed the presence of asbestos, though at concentrations they described as “generally low.” They resumed construction, but ordered measures to hold down dust, such as wetting down work areas and excavating during period of calm or low winds.

Then last May, a study in the Journal of Thoracic Oncology suggested a link between naturally occurring fibrous minerals and what it described as an unusual pattern of mesothelioma cases in southern Nevada.

Nevada health department officials–pointing out that the mesothelioma rate in Nevada is about average—attacked the study as scaremongering and tried to block it by revoking access to data from the state cancer registry. The authors wound up using federal data instead.

The study said that while mesothelioma normally strikes older men with workplace exposure to asbestos, in southern Nevada there were more victims than expected among women and people under 55. This, the study said, “suggests that environmental exposure to mineral fibers in southern Nevada may be contributing to some of these mesotheliomas.”

The hazard assessment in the Custer National Forest was requested by Forest Service officials and involved about a dozen employees. The NIOSH team tested rocks and soil to confirm the presence of erionite, and fitted employees with air samplers to measure airborne particles.

The highest concentration was .36 erionite fibers per cubic centimeter of air–more than three times the recommended asbestos exposure limit of .1 asbestos fibers. However, the report said a direct comparison was not possible because there are no standards for erionite.

Kurt Hansen, district ranger for the Sioux district in Camp Crook, S.D., said the NIOSH report, which was released in November but drew little attention, contained “no real surprises” because staff had known for some time about the presence of erionite.

He said the precautions recommended by NIOSH, such as keeping vehicle windows closed, are worthwhile, but noted that in the northern Great Plains, which gets little rain but plenty of wind, “there’s just no way to avoid dust generation.”

NIOSH previously conducted a similar evaluation of a Bureau of Land Management area near Cody, Wyo. In that case, tests for erionite in rocks, soil and air were negative. However, tests for silica, another lung hazard, revealed that some employees were exposed above occupational limits.

This story reported by FairWarning (www.fairwarning.org), a nonprofit news organization focused on public health, safety and environmental issues.

John Adams began his professional career in 2001 in Idaho Falls, ID writing and editing for a variety of trade magazines. He covered topics ranging from potato and sugar beet farming to skate park and playground construction and maintenance. Adams started his newspaper career as the city government reporter for the Daily Jefferson County Union in Fort Atkinson, WI where he covered the City Hall, police, fire and local courthouse beats. In 2005 he joined the staff of the Missoula Independent in Missoula, MT where he worked as a staff reporter covering a wide range of issues including the environment,...