By Todd Neale, Staff Writer, MedPage Today
Published: December 10, 2010
CHICAGO -- A naturally-occurring, asbestos-like mineral may be placing residents of North Dakota -- and elsewhere in the U.S. -- at risk for malignant mesothelioma, researchers found.
Exposure to erionite, whose fibers are physically -- but not chemically -- similar to those of asbestos, has been tied to unprecedented rates of malignant mesothelioma in villages in Cappadocia, a region in Turkey, according to Michele Carbone, MD, PhD, of the University of Hawaii Cancer Center in Honolulu.
Over the past few years, Carbone and his colleagues -- including researchers from the Environmental Protection Agency (EPA), U.S. Geological Survey, and National Institute of Environmental Health Sciences (NIEHS) -- have characterized the erionite exposure in Dunn County, N.D., where the mineral has been included in gravel used to make roads over the past two to three decades.
Reporting at the Chicago Multidisciplinary Symposium in Thoracic Oncology, Carbone said that mean erionite exposures measured along roads, indoors, and inside vehicles traveling along contaminated roads are equal to or greater than those found in the village of Boyali, where malignant mesothelioma accounts for 6.2% of all deaths.
Exposures were lower, however, than those found in villages in which the disease accounts for 26% to 52% of all deaths.
Because erionite has a latency period of 30 years or more, Carbone said, an uptick in mesothelioma cases has not been seen in North Dakota, although there is concern for the future.
That concern is underscored by a recent study released by the North Dakota Department of Health and the EPA, which found that in 33 people who had high erionite exposure either from working in gravel pits or on road maintenance, there was a significant increase in the pleural changes compared with male transportation workers with low cumulative asbestos fiber exposure (17.6% versus 1.5%).
Erionite deposits are also present in 12 other states -- all in the western half of the country -- and Carbone said exposures in those areas are unknown.
He and his colleagues set out to compare exposures in the Turkish villages to those in North Dakota, taking air samples in both places.
Mean exposures in North Dakota were near the lower range of exposures found in Turkey.
The physical and chemical properties of erionite were similar in samples taken from both sites. In cultures of mesothelial cells, both North Dakota and Turkish erionite induced programmed cell necrosis and the release of the cytokines HMBG1 and TNF-alpha.
Those processes have been linked to mineral fiber carcinogenesis, Carbone said.
The same inflammatory effects were seen in rats exposed to the erionite samples.
Carbone said that people living in areas where erionite is found should not panic, because the risk of developing malignant mesothelioma is low, even for highly exposed populations. He cited a study of South African miners who had exposures to asbestos lasting 10 years or more. In that population, 5% developed the disease.
Study co-author Aubrey Miller, MD, MPH, senior medical adviser of the NIEHS, said immediate measures to cut off the exposures have been implemented in North Dakota. Although erionite is not a regulated mineral, the state has limited its use for state-funded projects, and has released advisories warning of the danger. Roads containing erionite will be paved over.
Carbone and his colleagues have also begun studying biomarkers for the early detection of mesothelioma, which cannot be treated when it spreads but may be treated with some impact in its early stages.
But the best way to manage malignant mesothelioma is to prevent it from developing in the first place, said Roy Herbst, MD, PhD, of the University of Texas MD Anderson Cancer Center in Houston, who moderated a press briefing at which the findings were presented.
And, he added, "even though mesothelioma rates are low, it's one of the diseases that clearly has a causative agent -- that being these fibers, asbestos or erionite -- so if we can try to prevent this, that will pay dividends for many years to come."
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