Study suggests rare cancer is linked to asbestos in soil
By David L. Beck, San Jose Mercury News, July 13, 2005
It’s long been known that certain kinds of workers, from plumbers to shipyard laborers, are exposed to potentially deadly asbestos at a higher rate than the general public. But a recent study has found that where you live increases your risk as well.
The study of naturally occurring asbestos by a team from the University of California-Davis Department of Public Health Sciences examined every case of a kind of lung cancer called malignant mesothelioma in California for a 10-year period — nearly 3,000 in all — and tracked where patients lived.
“People who lived closer to an asbestos source had a greater chance of having mesothelioma,” the study found, “and the chance decreased steadily as the distance increased” — about 6.3 percent for every 6.2 miles.
The study did not come up with a “ground zero” figure for the chances of suffering from mesothelioma if one lives right on top of an asbestos vein. It was done by overlaying state geologic maps with the addresses of all of California’s mesothelioma patients from the years 1988 to 1997, as gleaned from the state’s cancer registry.
Pancreatic-cancer patients were used as a control group. Geography apparently played no role among them.
Mesothelioma, a cancer of the lining of the lungs, can be touched off by even intermittent low-dose exposure to asbestos. It takes as long as 30 years to develop. It’s almost always fatal.
The good news is that it’s extremely rare. About 300 people a year die from it in California, about 2,500 nationwide. Most of those — estimates range as high as 90 percent — were exposed to asbestos at work.
About the same number of people nationwide die from exposure to secondhand smoke. But it’s harder to figure out how to eliminate proximity to asbestos as a risk factor, the study authors said.
“Dust is a little more challenging for us to tackle than passive smoking,” said biostatistician and co-author Laurel Beckett. “It’s easier to say, `Please smoke outside’ than to say, `Dust — go away.’ ”
Asbestos is a naturally occurring mineral found most often in formations rich in iron and magnesium. In California, those formations are found mostly in the Sierra Nevada and its foothills and in the coastal range.
“We have a lot of asbestos in the northwestern part of the state,” said Marc Schenker, who headed the study, “but we don’t have a lot of people up there, and we don’t have a lot of building.”
Building — cutting through the ground, disturbing the soil, driving on unpaved roads — is a key factor in raising asbestos dust.
The foothills east of Sacramento are experiencing heavy growth. El Dorado County is already the site of a federal Environmental Protection Agency study.
The UC-Davis study, to be published in the American Journal of Respiratory and Critical Care Medicine this fall, did not suggest that neighborhoods built on potentially asbestos-bearing soil should be moved.
But its authors did say naturally occurring asbestos ought to be a factor in future risk assessments — an idea the state Department of Toxic Substance Control is already pursuing. It has found 17 actual or potential school sites, including Ramblewood Elementary in San Jose, that sit atop soils that could be rich in asbestos.
The study represents progress, said Schenker, “in that it adds a critical piece to our scientific understanding. We’ve got occupational studies, studies in Turkey and Greece,” where naturally occurring asbestos frequently finds its way into local building materials. “We have the toxicology. And now we’ve filled that in with the human study, if you will: Yes, there is a health hazard.”
“Remember,” he added, “it’s still a rare cancer.” In El Dorado County, the rate of mesothelioma is about two cases a year. “But that could go up,” said Schenker, “and we’d like to prevent it.”