Contracts,
permits and building codes aside, developers in California now have an additional
consideration before excavating for a new tract of homes: carcinogenic rocks.
Researchers say that residents living close to the state’s natural asbestos-containing
rocks face an increased risk for cancer.
Tremolite asbestos ranges in color from
white to grayish-green and occurs naturally in California. According to new
research, residents living close to asbestos-containing rock deposits may face
health risks if the asbestos particles are freed from the rocks. Image courtesy
of the California Geological Survey.
For up to 5,000 years, people have taken advantage of the fire-resistant and
strengthening properties of asbestos minerals. Throughout the 20th century,
however, the mineral started gaining recognition as an occupational hazard in
the air around sites such as mines, renovated and demolished buildings, landfills
and shipyards. But asbestos also affects some unsuspecting residents living
in California, says Marc Schenker, professor and chair of the Department of
Public Health Sciences at the University of California, Davis. When particles
are freed and swept into the air from specific asbestos-harboring rocks via
erosion, development or some other means, populations in close proximity breathe
in the harmful fibers.
“It is something that should be paid attention to,” says Schenker,
who, with colleagues, is publishing a study this fall in American Journal
of Respiratory and Critical Care Medicine on the connection between naturally
occurring asbestos and cancer. “It is a real hazard and does cause a malignant
and untreatable cancer.”
Once inside the body, asbestos can become stuck in the protective lining of
the lungs or other parts of the respiratory tract. And continued exposure may
lead to mesothelioma, a rare and often fatal form of cancer that affects the
lungs, abdomen and heart, researchers say. Specific cases of the disease, however,
are often difficult to link to an asbestos source because almost all of the
cases take 20 or more years after the initial exposure to arise, says Catherine
Skinner, a research affiliate in the Department of Geology and Geophysics at
Yale University. “The cancer is not the sort of one that turns up the day
after you’ve been exposed.”
To identify a link, Schenker and co-authors looked to ultramafic rocks that
they knew produce tremolite, one of the six fibrous minerals that fall under
the term asbestos. Dark-colored rock that formed from molten material deep in
the planet, ultramafic rocks can be exposed at Earth’s surface following
uplift or erosion processes.
Using a state map created by the California Department of Conservation, Division
of Mines and Geology, the researchers identified sites of surface ultramafic
rocks likely to contain asbestos (most of which can be found in the mountain
ranges of Northern and Central California) and the locations of nearly 3,000
patients diagnosed with mesothelioma over nine years. The patients’ addresses
came from the California Cancer Registry, Schenker says, which holds cancer
incidence and mortality statistics on close to 99 percent of all mesothelioma
cases diagnosed in the state.
The relatively large sample, when adjusted for gender, age and occupational
exposure, allowed Schenker’s team to see a trend that agreed with his hypothesis
that proximity to ultramafic rocks could be linked to mesothelioma. Their results
show that the chance of developing the cancer dropped by about 6 percent for
every 10 kilometers farther from an ultramafic rock source that a person lived.
Instances of mesothelioma remain rare, with only about 2,500 people per year
dying from the disease, which is slightly fewer than the number of people killed
from secondhand smoke during the same time, according to the National Institute
of Occupational Safety and Health. But some geologists are alarmed by the health
risk posed by tremolite, including Bruce Hilton, a senior engineering geologist
for Kleinfelder, Inc., in Sacramento, Calif. “I have felt that there is
building evidence that the risk is very real, but to what extent, we cannot
say,” Hilton says.
Skinner, however, cautions against drawing conclusions without an analysis of
the types and levels of asbestos particles that become airborne, and the mechanisms
involved that trigger the onset of mesothelioma. “I think it is hard to
relate mesothelioma, a very rare cancer, to only one hazardous source, asbestos,”
Skinner says. “Further, only a very small amount of these California ultramafic
deposits would have asbestos.”
“Recent studies by forensics and pathology experts such as Dr. Schenker
may resolve many questions and allow us to do good science,” Hilton says.
Schenker says that more field studies are needed to find answers to the remaining
uncertainties. In the end, he hopes that additional research will provide data
for developing public policies to reduce the risk of mesothelioma to California
residents.
Kathryn Hansen
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