Investigating erionite, asbestos' more carcinogenic cousin

by Mary Caperton Morton
Wednesday, April 19, 2017

Blocks of volcanic tuff quarried from this mine in Turkey contain carcinogenic erionite. Credit: F. Mighali (Kaltun Italia S.r.l.).

Asbestos is notorious for causing lung cancer and other respiratory diseases, but it’s not the only type of fibrous mineral that affects human health. In the mid-1970s, erionite was linked to the unprecedented high mortality rate from mesothelioma in villages in central Turkey where volcanic tuff had been used as a building material for centuries. Like asbestos, erionite can occur as long thin fibers that, when inhaled, can persist in lung tissue for decades. New research looking at associations of iron with erionite is helping pathologists better understand why embedded erionite fibers sometimes lead to lung cancer.

Since the mesothelioma epidemic in Turkey began, in vivo and in vitro studies have confirmed the carcinogenicity of erionite, says Alessandro Gualtieri, a mineralogist at the University of Modena and Reggio Emilia in Italy, and lead author of a study in Scientific Reports detailing the new work. “But we still know little about the mechanisms at the molecular scale that lead to disease,” he says.

Researchers have suggested that the problem can be traced to iron associated with the erionite fibers, as is the case with asbestos, says Victor Roggli, a pathologist at Duke University who was not involved in the new study. “With asbestos, iron gets adsorbed onto the surface of the fibers and when the fibers get embedded in the lungs, the iron sets off redox reactions that cause tissue damage, which can eventually lead to malignancy.”

Gualtieri and colleagues used electron microscopy to examine erionite samples at high resolution. They found that the iron was not embedded in the mineral’s crystal structure, as had generally been assumed. Instead, iron was present in association with impurities and accompanying minerals, and so was only attached to the erionite indirectly. “If iron is not part of the [mineral] structure, its role should be considered irrelevant for erionite toxicity, and other factors like biopersistence should be invoked,” Gualtieri and his colleagues wrote.

Roggli says that iron’s role in causing disease can’t be fully ruled out yet. But, he says, the erionite fibers themselves could also be the main culprit, perhaps affecting the splitting of chromosomes in cell division, which has also been shown to lead to cancer.

Erionite appears to be even more toxic than asbestos, Gualtieri says, most likely due to its high level of biopersistence, the length of time it can exist in the body. “If you inhale it, the fibers will stay in your lungs for the rest of your life.” Some types of asbestos dissolve in a matter of months, though others can persist much longer.

Cases of erionite-related mesothelioma have been few outside of the cluster in Turkey and another cluster in central Mexico, but the mineral, formed when volcanic ash is altered by water, is also found in rocks across the western U.S., including in Arizona, California, Nevada, North Dakota, Oregon and Wyoming. Samples from different locations also appear to have varying levels of toxicity based on the length of the fibers, Gualtieri says. “Fortunately, it has no applications or industrial uses, unlike asbestos,” he says, so exposure to the mineral is rare.

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