Asbestos in rocks cause lung cancer

According to a study by a team at UC Davis Department of Public Health Sciences, everyday exposure to naturally occurring asbestos, increases the risk of developing malignant mesothelioma.

It has long been recognized that exposure to asbestos in the workplace, particularly in shipyards, is a risk factor for mesothelioma, a rare form of cancer which affects the lining of the lung.

But in this new study, researchers found an association between mesothelioma and living near to ultramafic rock, the main source of naturally occurring asbestos.

Marc Schenker, professor and chair of the UC Davis Department of Public Health Sciences and the study's senior author, says the study shows that naturally occurring asbestos causes mesothelioma, and though the risks are low they should be taken seriously.

According to National Institute of Occupational Safety and Health statistics, mesothelioma kills about 2,500 people each year, the same number of Americans as die from passive smoking.

Ultramafic rock is found throughout the Sierra Nevada, Coast Ranges and Klamath Mountains in Northern and Central California, and new housing developments raises concern as especially areas of ultramafic rock linked to tremolite asbestos.

Schenker and his team used the California Cancer Registry data to identify 2,908 cases of malignant mesothelioma diagnosed between 1988 and 1997 in adults ages 35 and older.

A control group of an equal number of age and gender matched pancreatic cancer cases was selected,( pancreatic cancer has no known association to asbestos exposure).

For both the groups, the researchers used a map from the California Department of Conservation, Division of Mines and Geology as the reference for ultramafic rock deposits.

Statistical adjustments were then made for sex, occupational asbestos exposure and age at diagnosis.

The researchers found that the risk of developing malignant mesothelioma was directly related to living close to a source of ultramafic rock, and the odds fell by 6.3 percent for every 10 kilometers (about 6.2 miles) farther a person lived from the nearest asbestos source.

The association was strongest in men, but was also seen in women. No such association showed up in the pancreatic cancer group.

Jerrold L. Abraham, professor and director of environmental and occupational pathology at Suny Upstate Medical University in Syracuse, New York, and a leading authority on mesothelioma, says this is the strongest evidence connecting living near deposits of naturally occurring asbestos and mesothelioma.

Laurel Beckett, professor and vice chair of the UC Davis Department of Public Health Sciences and a study co-author, said the findings are important, and comparable to the link between lung cancer and passive smoking.

California has one of the largest cancer databases in the world. An estimated 98.9 percent of all mesothelioma cases diagnosed in California are reported to the registry, and it's size enabled researchers to identify an association that might not have been apparent in a smaller study.

Schenker says that more research is needed to examine the effects of exposure to naturally occurring asbestos.

He says because mesothelioma takes 20 to 30 years to develop, knowledge gained will help to protect Californians from this preventable cancer decades into the future.

The study will be published later this year in the American Journal of Respiratory and Critical Care Medicine.