Here's another reason to hold your breath while driving through a tunnel: you could be saving yourself from inhaling erionite, a natural rock mineral fiber present in road gravel that, like asbestos, can accumulate in lung tissue over time and cause malignant mesothelioma. Mesothelioma is a rare cancer that affects the protective lining of internal bodily organs, most commonly the lungs due to asbestos exposure. Currently, the World Health Organization estimates that 125 million people are occupationally exposed to asbestos and over 107,000 deaths each year are attributed to asbestos-related mesothelioma.

Prompted by the malignant mesothelioma epidemic caused by erionite exposure in Turkey in 1978 and emerging cases of erionite-associated disease in North America, scientists headed by Dr. Michele Carbone from the University of Hawaii Cancer Center published a new study in the Proceedings of the National Academy of Sciences where they compared erionite from North Dakota with that found in Turkish villages affected by the mesothelioma epidemic.

In the study, the researchers measured airborne concentrations of the mineral in various settings, studied its chemical composition, and analyzed its biological activity. When mice were injected with the erionite from Dunn County, their lungs showed signs of inflammation and abnormal cell growth, precursors to mesothelioma. Under the microscope, the fiber size of the erionite from North Dakota was similar to that of the Turkish erionite. Overall, the researchers found no chemical differences between the North Dakota erionite and samples of the cancer-causing mineral from Turkey. The airborne levels of erionite in North Dakota were comparable to levels found in Turkish villages with 6-8 percent mortality rates from mesothelioma, the researchers reported.

"Based on the similarity between the erionite from the two sources," says Carbone, "there is concern for increased risk of mesothelioma in North Dakota." The long latency period of the disease—it can take 30 to 60 years of exposure to cause mesothelioma—and the fact that many erionite deposits have only been mined in the past few decades suggests that the number of cases could soon be on the rise. In addition to North Dakota, California, Oregon, Arizona, Nevada and other states have erionite deposit, but the possibility of human exposure elsewhere in the U.S. has not yet been investigated.

In contrast to asbestos, which causes mesothelioma at lower rates, there are no established health benchmarks in the U.S. on safe levels of erionite exposure, because until recently, physicians thought that erionate was present only in Turkey. The new findings, however, indicate that precautionary measures should be put in place to reduce exposure to the mineral, says Carbone. In Turkey, his earlier findings led to moving villagers away from areas with high levels of erionite, into new housing built out of erionite-free materials. "Our findings provide an opportunity to implement novel preventive and detection programs in the U.S. similar to what we have been doing in Turkey," he says. Future studies could analyze erionite levels in other areas of the U.S. and develop strategies to prevent and screen for mesothelioma. The study was funded through grants from the National Cancer Institute and the 2008 AACR-Landon Innovator Award for International Collaboration in Cancer Research to Michele Carbone.

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Original research article