Although the often fatal cancer known as mesothelioma is almost always associated with asbestos, a new study has found that environmental exposure to a (nonasbestos) volcanic mineral, erionite, may be just as dangerous.
The study, published in the March 15 issue of the Journal of the National Cancer Institutefound a high incidence of mesothelioma among people living in a region of Turkey where erionite is plentiful and commonly used in construction and produce storage rooms.
Previous reports suggest that erionite exposure is associated with a higher risk of cancer development than any other natural mineral fiber tested.
The researchers from Hacettepe University in Ankara, Turkey, followed 891 people age 20 years and older in three Turkish villages for 23 years. Two of the villages were exposed to erionite and one (the control) was not.
During this period, 372 deaths occurred, and 119 of these deaths occurred from mesothelioma. That figure represented 44.5% of all deaths in the two villages with erionite exposure.
Only two cases of mesothelioma occurred in the control village, both in people born outside of the control village.
The mortality data were analyzed jointly with Dr. Philippe Grandjean of the Harvard School of Public Health. When compared to the worldwide standardized annual incidence of pleural mesothelioma the two exposed villages had a pleural mesothelioma rate of  200 and 700 cases per 100,000 people annually. The rate in the non-exposed village was only 10 cases per 100,000 people each year.
This enormous discrepancy led the study authors to conclude that the long-term exposure to erionite is the cause of the extraordinarily high risk of developing mesothelioma.
Since millions of people are exposed to erionite mineral fibers in rural areas of Turkey, the researchers urge that resources “should therefore be directed to preventing these environmental exposures and additional study of the association between environmental exposure to nonasbestos fibers and the risk of cancer.”
This alarming finding comes on the heals of a similar study published in the second issue of the October 2005 of the American Journal of Respiratory and Critical Care Medicine of the American Thoracic Society, that found Californians who live near naturally occurring asbestos sources and who are exposed to low levels of the mineral are at increased risk for developing malignant pleural mesothelioma, a serious cancer of the membrane covering the lung.
Dr. Marc B. Schenker, of the Division of Environmental and Occupational Health, at the University of California, Davis, and four associates, examined 2,908 malignant mesothelioma cases reported from 1988 to 1997.
Over 50% of the men and 58% of the women, all of whom were listed in the California Cancer Registry, either had no or little exposure to occupational asbestos at the workplace.
“People who lived closer to an asbestos source had a greater chance of having mesothelioma, and the chance decreased steadily as the distance increased,†said Dr. Schenker.
Mesothelioma is considered to be rare. It usually develops 30 to 40 years after exposure. It has been widely believed that the only known cause of the disease is exposure to asbestos fibers, which can cause tumors in the pleura, the two layers of membrane covering the lung, or, with more intense exposure, in membranes of the abdomen.
According to the study authors, California has more naturally occurring asbestos source rocks than any other state in the U.S.
Previous studies all point to occupational exposure to asbestos as the cause of mesothelioma. But population-based studies, Dr Schenker says, have almost all showed some examples of mesothelioma cases where there was no exposure at work. The new study reveals that the living environment could actually be the culprit in such cases.
The Turkish study would now seem to show that erionite mineral fibers pose the same or greater risk of mesothelioma development as asbestos.
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