by Sara E. Pratt Monday, January 30, 2012
As North Dakota’s state geologist, Ed Murphy has spent a fair amount of time mapping the geology of the Killdeer Mountains in the western part of the state, hiking up and down buttes of the White River Group and the Arikaree Formation. In the 1980s, he and colleagues mapped large deposits of rocks bearing erionite — a zeolite mineral formed when volcanic ash is altered by water — that may have had some commercial use. No use was ever found for the mineral itself, but for roughly 30 years, several gravel-mining operations have been excavating the chalky, grey-brown rock from these erionite-bearing formations. It was then crushed and spread on nearly 500 kilometers of roads in Dunn County, as well as on playgrounds, baseball fields, parking lots and even flower beds.
Murphy didn’t hear much about erionite again until 2005, when he received a phone call from Nels Forsman, a geology professor at the University of North Dakota who, as a post-doc working with the state geological survey in 1986, had identified erionite deposits in the northwestern part of the state.
Forsman had just heard a talk on the medical geochemistry of earth materials by Geoff Plumlee, a geochemist at the U.S. Geological Survey (USGS) in Denver, Colo., who had mentioned erionite occurrences in the United States. He also mentioned the unprecedented rates of malignant mesothelioma that the asbestos-like mineral causes in some villages in the Cappadocia region of Turkey.
“We were trying to find an industrial use for it; we had no idea it was potentially carcinogenic,” says Murphy, who immediately contacted the state Department of Health. “It just never dawned on us.”
The discovery that some North Dakotans may have been breathing erionite-contaminated gravel dust for decades — and now face an uncertain future risk of mesothelioma, a deadly cancer that takes decades to appear — also raises concerns about the health and safety of workers and residents in the other 12 western states where erionite is found.
The concerns are not unwarranted, as the mineral has killed before. In Central Anatolia, Turkey, an epidemic of mesothelioma — a normally very rare cancer of the smooth lining of the chest, lungs, heart and abdomen — is responsible for up to almost 50 percent of the deaths in some villages.
The disease is caused by the inhalation of needle-like fibers that bore through the lungs and lodge in tissues elsewhere in the body. In the U.S. each year, 2,500 people die from mesothelioma — that’s a rate of about 14 deaths per million people ages 25 and up — mostly due to occupational asbestos exposure. However, the high rates of mesothelioma observed among residents of the Turkish villages of Karain, Tuzkoy, Old Sarihidir, Karlik and Boyali have been related to erionite, not exposure to asbestos. The anomaly drew an international team of researchers there in the late 1970s when the epidemic was first reported by Izzettin Baris, a pulmonary physician at Hacettepe University in Ankara.
Based on mineralogy and lung tissue samples, erionite — found locally in the volcanic tuff from which villagers built their homes — was soon discovered to be the culprit. In 1987, the International Agency for Research on Cancer classified erionite as a known human carcinogen and concluded there was a causative link between erionite and the malignant mesothelioma epidemic in Turkey. In 1994, erionite was first listed in the Annual Report on Carcinogens published by the U.S. Department of Health and Human Services' National Toxicology Program.
That information, however, is not widely known in the U.S., where erionite was first described by Harvard mineralogist Arthur Eakle in 1898 from samples collected in Oregon. Erionite deposits have since been found on every continent, including Antarctica, and in 12 western U.S. states in addition to North Dakota.
Some of the earliest deposits in the U.S. were discovered in Rome, Ore., (pdf) which was named after the column-like erionite-bearing rock formations outside of town. Rome has since been the source of many of the erionite samples used to determine the mineral’s toxicity. Animal tests suggest that erionite is up to 800 times more likely to cause tumors than the chrysotile form of asbestos and 200 times more likely to cause tumors than the crocidolite variety of asbestos. In some studies of rats exposed to erionite fibers, malignant mesothelioma developed in 100 percent of cases.
“Erionite is almost certainly the most toxic naturally occurring fibrous mineral known,” wrote Umran Dogan, a biochemical and geological engineer at the University of Iowa and Ankara University in Turkey who has worked in the Turkish villages, in a 2008 Environmental Geochemistry and Health article.
Despite the evidence, erionite remains an unregulated material in the United States, because it has not been used commercially and it was thought until recently that, unlike with asbestos, human exposure was extremely limited, says Dr. Aubrey Miller, senior medical advisor at the National Institute of Environmental Health Sciences (NIEHS) in Bethesda, Md., who has studied asbestos-related disease in Libby, Mont., as well as the mesothelioma epidemic in Turkey, and is now investigating Dunn County, N.D. Over the last several decades, however, expanding development and road building in rural areas in the U.S. has brought more people into contact with the mineral.
The first case of erionite-related lung disease in North America was identified in Utah in 1981 in a man who had been a road construction worker and lived near zeolite deposits. The first confirmed case of erionite-related mesothelioma in North America was identified in Mexico in 2008. That same year, a mesothelioma cluster was reported in a small village in a zeolite-rich region of central Mexico. In 2009, another case of mesothelioma was reported in a man who had lived in both Mexico and the United States and had substantial amounts of erionite in his lungs.
After Murphy sounded the alarm in North Dakota in 2005, researchers quickly mobilized to investigate.“The first question the state had was: Should we be worried?” says Miller, who was working with the U.S. Environmental Protection Agency (EPA) at the time.
To answer that question, samples of the road gravels needed to be collected for testing, which Murphy did personally. “What we knew at the time was that the fibers were in the caprock of these buttes, and the buttes were surrounded by pediment gravels, and the gravels were being put on roads,” he says. “What we didn’t know was whether the fibers were surviving through gravel processing and making it onto the road.”
The results came back in the spring of 2006. Erionite fibers were making their way from the caprock to the pediment gravels and onto the road surface, although the size and the amount of fibers both decreased along the way. In 2009, Murphy’s team ran an additional 50 rock samples from the White River Group and Arikaree Formation, which cover 160 square kilometers in southwestern North Dakota, and found erionite fibers in the majority of samples.
After finding it on the roads, researchers began to assess how much erionite dust the 3,000 residents of Dunn County may have been exposed to and how it compared to the exposures found in Turkey. They also began a medical evaluation of those suspected of high dust exposures, including road maintenance crews, quarry workers, bus drivers and mail carriers.
The results of the studies have been coming in over the past few years, culminating in the first workshop on erionite-related diseases, which was held in October 2011 and attended by many of the government scientists and academic researchers studying the issue, as well as public health officials from North Dakota. “We got all the research together and compared it,” Miller says, “and what we’re finding is not good.”
The final results of the medical study conducted by the University of Cincinnati College of Medicine in Ohio were reported in October 2010 (pdf). Of the 34 people who volunteered to get chest X-rays and CT scans — including Murphy and the state paleontologist, who had recovered fossils from erionite-bearing formations — two people, both of whom had worked on road maintenance crews, showed scarring in the lungs thought to be related to their erionite exposures. Overall, 17.6 percent of participants exhibited changes to their lung tissue, which are potentially early signs of increased risk for lung cancer or mesothelioma. In the regular population, only about 1 percent would be expected to have similar lung changes, generally associated with asbestos exposure.
“The lung scarring couldn’t be explained by any other exposure,” Miller says. “So that’s something to be concerned about.”
In 2008, another team, led by Michele Carbone, a cancer geneticist at the University of Hawaii Cancer Center in Honolulu, and involving the EPA, Miller, and researchers from USGS, traveled to Turkey to collect indoor and outdoor air and dust samples in villages with and without high rates of mesothelioma. A geologic analysis of the samples, conducted by Heather Lowers and colleagues at USGS in Denver at the request of the EPA, compared them with erionite collected from the Killdeer Mountains and from Rome, Ore. The results of the comparative study, published in 2010, found the chemistry and morphology of erionite in North Dakota to be similar to that in Turkey. “From a public health standpoint,” Miller says, “we were highly concerned about ongoing exposures in the United States from this material.”
Additionally, levels of erionite exposure that people in North Dakota were experiencing inside and outside homes and vehicles, including school buses, were compared to the levels found in Turkey. In North Dakota, residents may not have built their homes from erionite-bearing stone as had the villagers in Turkey, but levels of erionite in air samples taken along gravel roads in Dunn County were as high as outdoor air levels seen in Turkish villages with mesothelioma death rates ranging from 20 to 50 percent. Overall, erionite levels in air samples in North Dakota equaled or exceeded those in the village of Boyali, where the mesothelioma death rate of 6.25 percent is lower, but still significant, the team reported last year in Proceedings of the National Academy of Sciences.
One of the mysteries surrounding erionite exposure, however, is that not everyone who is exposed to even high levels of erionite (or asbestos) develops mesothelioma. One reason may be genetics: Carbone and colleagues reported in Nature in 2007 that some of the families in the Turkish villages have a genetic mutation that predisposed them to mineral fiber carcinogenesis, making them especially susceptible to erionite exposure. The team is now searching for blood markers that could be used to identify the disease early, allowing for intervention and treatment.
Despite such potentially dire news, many longtime residents of North Dakota, where no cases of mesothelioma have yet been reported, are skeptical of the problem. Nevertheless, state and county officials have been working with the EPA to clean up some of the areas where children would most likely be exposed, including ball fields, playgrounds, schools and the parking lot at a community pool.
However, exposures are still ongoing. Although Dunn County itself is no longer using erionite-containing gravel to maintain county-owned roads, the gravel that was already in place has not been removed and paving over it has been deemed too costly. In 2007, the North Dakota Department of Transportation banned the use of erionite gravels on state roads and issued guidelines suggesting that gravel not be mined from exclusion zones within a certain radius of known erionite deposits, and that gravel from a wider radius be tested for erionite before being used. And the U.S. Forest Service recently required a contractor to remove erionite-bearing gravel that had been placed on a forest service road in western North Dakota. Nonetheless, the state has no regulatory authority to prevent the use of erionite-bearing rock on private roads and property.
In Dunn County, there are few other sources of gravel nearby, so if maintenance crews are not using the erionite-containing gravels, the roads must be maintained with gravel trucked in from other quarries, which costs more. “If you don’t keep the roads maintained with gravel, there are safety issues,” Murphy says. “That’s also a very real problem.”
“They’ve taken steps to remediate areas where children are likely to be exposed to erionite, but after that it is about risk and cost-benefit analysis,” says Maeve Boland, a geologist who was an American Geophysical Union Congressional Science Fellow in the office of North Dakota Sen. Byron Dorgan from 2009 to 2010. “We only have so much money and there are so many miles of gravel roads.”
Miller says he finds any use of the gravel disconcerting. “You certainly don’t want to continue to use gravel that is contaminated with erionite and keep putting people in harm’s way,” he says. “The goal is to get people not to use it in order to reduce exposure and disease, and in that regard the current state and federal regulations are not effectively protecting public health.”
In Dunn County, dust control on unpaved roads was already an issue due to increased truck traffic from the oil boom in the Williston Basin’s Bakken Formation, which underlies the county. Oil-related truck traffic affects about a third of the county’s roads, and some stretches of road can see thousands of vehicles a month. Complaints about billowing clouds of dust from residents living along “haul roads” prompted the county to institute dust control measures, including spraying the roads with heavy magnesium chloride solutions, which are expensive and, by some accounts, not very effective. With each passing truck, however, erionite fibers can be resuspended.
“One thing we learned from asbestos in Libby is that once it’s out there it doesn’t go away,” Miller says, “it just keeps giving off fibers for years and years and years.”
Although no federal regulatory standards exist, the discovery in North Dakota that the mineral is being disturbed and the population is being exposed has prompted a wider look at the handling of erionite nationwide.
In October 2011, an interdisciplinary workshop organized by NIEHS brought together more than 30 scientists, including geologists, environmental toxicologists and cancer researchers representing multiple institutions, to discuss the state-of-the-science on erionite-related disease, raise awareness of the hazards, and address how to move the research forward. “We need to be doing more to educate the public about the risks associated with this and not bury our heads in the sand, or in this case, the gravel,” says Miller, who organized and chaired the meeting.
In November 2011, the Centers for Disease Control and Prevention and the National Institute for Occupational Safety and Health released the first national advisory on occupational erionite exposure (see sidebar, print exclusive).
In addition, USGS has begun a new project to update a 1996 USGS map of known locations of erionite in the United States. The new map being developed will identify additional erionite occurrences, distinguish between fibrous and nonfibrous erionite, and indicate whether deposits are surficial or in deep bore holes. (Fibrous erionite that has become airborne is thought to pose the greatest hazard.) Plumlee says that the new map, when completed, will help public health experts understand better the areas where erionite exposures are potentially an issue. Plumlee is overseeing the effort along with Brad Van Gosen, also at USGS, who created a similar map for U.S. asbestos locations.
“Earth scientists can help determine what people could be exposed to and where these exposures could occur,” Plumlee says. “Forewarned is forearmed.”
Ultimately, combining geologic maps and epidemiological data could possibly reveal previously unknown disease clusters, by looking near known erionite deposits, or it could help uncover previously unknown hazardous erionite deposits, by searching near disease clusters.
“Sometimes,” Miller says, “you don’t see things until you start looking for them.”
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