Exposure to Asbestos from rocks

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Exposure to Asbestos from Rocks Can Cause Malignant Mesothelioma

Category: Lung Cancer News

Article 17 Oct 2005

 

 

 

 

 

Californians who live close to naturally occurring asbestos sources

and who are exposed to low levels of the mineral are at increased

risk for developing malignant mesothelioma, a serious cancer of the

membrane covering the lung, according to a new study published in the

second issue of the October 2005 American Thoracic Society's American

Journal of Respiratory and Critical Care Medicine.

 

Marc B. Schenker, M.D., M.P.H., of the Division of Environmental and

Occupational Health, at the University of California, Davis, along

with four associates, investigated 2,908 malignant mesothelioma cases

reported over a 10-year period (1988 to 1997). Over 50 percent of the

men and 58 percent of the women, all of whom were listed in the

California Cancer Registry, either had no or low occupational

exposure to asbestos.

 

" 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.

 

According to the article, the odds of developing mesothelioma

decreased 6.3 percent for every 10 kilometers farther from the

asbestos source.

 

The authors explained that a major strength of the study was the very

large number of mesothelioma cases used to assess the potentially

weak association between exposure to naturally occurring asbestos and

mesothelioma incidence.

 

" Epidemiological studies have confirmed that occupational exposure to

asbestos causes mesothelioma, " said Dr. Schenker. " However, almost

all population-based studies have found that many mesothelioma cases

had no known occupational exposure to asbestos. "

 

Considered rare, mesothelioma usually takes from 30 to 40 years after

exposure to develop. The only know causes is exposure to asbestos

fibers, which can cause tumors in the two layers of membrane covering

the lung (the pleura), or, with greater exposure, in membranes of the

abdomen.

 

According to the authors, California has more naturally occurring

asbestos source rocks than any other state in the U.S., but their

distribution is patchy, with exposed areas separated from unexposed

areas. The group used Geographic Information Systems (GIS) software

to pinpoint the sources of asbestos and the location of patient

residencies more precisely.

 

" Geocoding of residential addresses provided a more accurate

assessment of potential environmental exposure to naturally occurring

asbestos at the individual level than methods using a less precise

geographic classification, " said Dr. Schenker.

 

The California Cancer Registry includes occupational information, so

the researchers were able to control for, and the study confirmed,

the increased risks of mesothelioma among shipyard workers,

boilermakers, insulators, plumbers, steam fitters, and other

tradespeople involved in construction and shipping. In an editorial

on the article in the same issue, Marcel Goldberg, M.D., Ph.D., and

Danièle Luce, Ph.D., of the Institut National de la Santé et de la

Recherche Médicale (INSERM) in Saint Maurice, France, note that it is

of utmost importance, " from a scientific and public health point to

view, to know whether exposure to low levels of asbestos is able to

induce pleural mesothelioma. "

 

" While exposure in environmental settings is generally much lower

than in occupational circumstances, the levels may not be

negligible, " they write. " In studies in which elevated risk of

mesothelioma was demonstrated, people typically lived in close

vicinity of naturally occurring asbestos sources, and may have had

direct contact with asbestos, when white-washing houses with material

containing asbestos or working in polluted fields. It is thus likely

that lifelong cumulative exposure may have been as high (if not

higher) as in some occupational settings, but it was not-or not

adequately-measured, and non-occupational studies have not yet

provided adequate answers.

 

" That is why this work…showing a relationship between mesothelioma

risk and residential distance from naturally occurring asbestos, and

suggesting that there is excess risk of mesothelioma even at long

distance from the asbestos source, is important. To our knowledge,

this study is the first one that demonstrates such an effect quite

convincingly. "

 

The editorialists contend that additional research is now necessary

to more accurately assess the levels of cumulative exposure that

persons experience in areas where excess risk of pleural mesothelioma

was observed.

 

American Thoracic Society (ATS)

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