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Erionite is a naturally occurring fibrous mineral that belongs to a group of minerals called zeolites. 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 and has an internal molecular structure similar to chabazite. This mineral is likely as toxic as asbestos; however, erionite is not currently regulated by the U.S. Environmental Protection Agency and there are no occupational exposure limits for erionite fibers. Erionite was first described by A.S. Eakle in 1898, as white woolly fibrous masses in cavities in rhyolite lava near Durkee, Oregon. It was originally thought to be another relatively rare zeolite named offretite, which is very similar to erionite in appearance and chemical composition.
There is sufficient evidence of carcinogenicity of erionite in experimental animals. exposed to erionite by inhalation or injection (intrapleural or intraperitoneal) and mice exposed by intraperitoneal injection had a high incidence of mesothelioma. Additionally, although carcinogenic properties of erionite have been discovered by investigating the erionite found in Central Anatolia, Turkey, no difference in their carcinogenic capacity has been observed when it was compared to the erionite obtained in North Dakota, USA.
In the past, occupational exposure occurred from erionite mining and production operation. Nowadays potential occupational exposure to erionite usually occurs during the production and mining of other zeolites. Erionite was also reported to be a minor component in some commercial zeolites.Mondale, K. D., F. A. Mumpton and F. F. Aplan. 1978. Beneficiation of Natural Zeolites from Bowie, Arizona: A Preliminary Report. In Natural Zeolites: Occurrences, Properties, Uses. L. B. Sand and F. A. Mumpton, eds. New York: Pergamon Press. p. 527-537. Therefore, the use of other zeolites may result in potential exposure to erionite for the workers and the general population who use the zeolites in a variety of processes and products. Total dust exposures for miners in an open-pit zeolite mine that contained some erionite in Arizona ranged from 0.01 to 13.7 mg/m3; respirable dust in the mining area was 0.01 to 1.4 mg/m3. Erionite is held responsible for the high incidence of asbestosis and various forms of lung cancer within the Turkish village of Tuzkoy near Nevsehir in the popular tourist region of Cappadoccia.
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