Erionite is a naturally occurring, microscopic, fibrous mineral. It usually is found in volcanic ash that has been altered by weathering and ground water. Erionite forms brittle, wool-like fibrous masses in the hollows of rock formations. Its color varies from white to clear, and it looks like transparent, glass-like fibers. Erionite has been found in at least 12 states, including North Dakota. Some properties of erionite are similar to the properties of asbestos; however, currently erionite is not one of the six asbestos fibers regulated by the U.S. Environmental Protection Agency (EPA)

Like asbestos, erionite may pose health risks to those who breathe in the fibers. It appears to be associated with increased risks of fibrogenic lung disease, lung cancer and mesothelioma (a rare type of respiratory cancer usually related to asbestos exposure). These health risks were first documented in a study of three small villages in Turkey in the 1970s, where roads, homes, and other buildings were built into, or made of, material containing erionite. However, there have been few studies of erionite’s health effects on populations in the United States, due in part to challenges in studying the mineral.

Over the past few decades, gravel pits have been excavated in western North Dakota where naturally occurring erionite is found. The gravel was used to surface local county roads, parking lots and other areas. In 2006, the North Dakota Department of Health, now the North Dakota Department of Environmental Quality (Department), learned of the potential health effects of erionite and its occurrence in North Dakota through discussions with the University of North Dakota (UND) and the North Dakota Geological Survey (NDGS). The Department immediately began investigating the situation, in cooperation with the NDGS.

Gravel deposits that contain erionite are located in or near the Arikaree, Brule and Chadron geologic formations, which correspond to the Chalky Buttes, Little Badlands and Killdeer Mountain areas in Slope, Stark and Dunn counties. These geologic formations are also present in other high buttes in western North Dakota, but testing has not been done to see if erionite is present there, as well.

Since learning of the potential health risk, in 2006 testing was done on samples from Dunn County, the area where North Dakota's naturally occurring erionite first became a concern.

The NDGS tested some of the rock faces of the Killdeer Mountains and nearby gravel piles that had been excavated from areas suspected of containing erionite. Laboratory tests showed that erionite fibers were present in many of the samples. The Department then met with county commissioners afterward in 2006 to bring the situation to their attention and discuss sampling results. A public meeting was later held to provide local residents with information about erionite in Dunn County. The Department then asked EPA to conduct an investigation of the possible health effects of erionite exposures in Dunn County.

In cooperation with North Dakota, EPA took air and soil (soil, rock, and dust) samples in 2006 and 2008 to determine if the erionite in Dunn County is similar to the erionite that has been associated with health effects in other parts of the world. Soil samples were taken from suspected erionite source areas such as directly from rock formations and gravel pits, as well as areas where suspected erionite material was used such as in roads, parking lots, and play yards. Air samples were taken from suspected erionite sources to determine the ability of erionite to become airborne during dusty activities such as driving, sweeping, and road maintenance.

The testing showed that the erionite fibers were present in some of these areas and are of the size and shape that can be easily inhaled if they are disturbed and become airborne.

It was decided that the next step would be to conduct a medical study, involving individuals with the highest risk of exposure; primarily gravel pit operators, road maintenance personnel, and those with jobs involving frequent driving on gravel roads such as postal workers and school bus drivers. With EPA and the University of Cincinnati Department of Environmental Health, the study looked at 34 individuals and concurrently a statistical analysis was done on mesothelioma rates in North Dakota compared to the rest of the United States. While the statistical analysis concluded there was no mesothelioma increase or clustering of cases, the medical study did suggest that occupational exposure to road gravel containing erionite could result in changes to the lung tissue. Precautionary measures should be considered for those with occupational exposure to erionite, such as road maintenance and gravel pit workers.

Based on the results of the medical study, the Department continues to monitor the current erionite research as well as keeping the citizens of North Dakota informed of the issue. Further research into the cases in Turkey links a genetic predisposition in certain families there to the development of mesothelioma from erionite fibers, however the genetic link is still being studied. Other research is looking into the effects of erionite exposure in Mexico, Italy, Iran, and other parts of the United States such as Nevada.

In North Dakota, the Department is working with counties and businesses to restrict further use of gravel containing erionite. In addition, after consultation with the North Dakota Department of Transportation (NDDOT), the NDDOT has prohibited its use in NDDOT projects.

The extent of the erionite exposure in western North Dakota is unknown, but given the inherently toxic nature of the material, reducing exposure is recommended. Where found, erionite should not be disturbed. Mining should be prohibited in specific areas where erionite is known or suspected, and areas nearby should be tested for erionite before being mined (see testing & exclusion radius map below). Recommendations for county highway departments, businesses and private landowners include finding alternative sources of gravel and limiting or eliminating exposure to erionite fibers. Those with family histories of mesothelioma are particularly recommended to reduce or avoid exposure.

For more information specific to erionite, contact the Asbestos Program by email at asbestos@nd.gov, or you may call 701.328.5166