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Sierra gravel roads may bite the dust Gravel roads kick up cancerous dust
State considers paving hundreds of miles of byways where cars kick up cancer-causing clouds
By Ian Hoffman, STAFF WRITER
04/14/2005 - Many dusty byways of California's countryside could be headed for the past with mounting evidence that common road gravel made of the state rock can create invisible clouds of cancer-causing asbestos. State environmental regulators recommended this week that gravel roads be slathered in tar or asphalt to keep vehicles from sending asbestos fibers airborne, into the lungs of people walking or living close by.
The culprit is gravel made of the state rock, serpentine, which tests in the late 1980s showed can contain up to 90 percent asbestos fibers by weight. State officials don't know how much of California's unpaved roads could be affected but agree that paving them could cost several tens of millions of dollars.
In the latest of two decades ofstudies on asbestos-producing unpaved roads in California, scientists ran cars up and down a remote gravel road in El Dorado County and detected "significant" airborne asbestos fibers in air-sniffing devices up to 190 feet away, "despite the lack of visible dust."
At a roadside where rural schoolchildren wait for the bus, state and federal experiments in California foothills since the mid-1980s have shown that asbestos concentrations can approach the kind of workplace exposures that have produced cancer in asbestos miners, construction workers and brake-pad makers.
In the latest study, the California Department of Toxic Substances Control estimated that for every 100 people exposed 16 hours a day to dust from a high-speed, high-traffic serpentine gravel road over 70 years, as many as three could get lung cancer or the rarer mesothelioma, still thousands of times the usual regulatory target of one extra cancer in a million.
That comes from a serpentine-gravel road in Garden Valley with an asbestos content of 2 percent by weight, which is low compared to gravel tested elsewhere by state regulators. Yet it is twice the "action level" that EPA Superfund officials use as a trigger for cleaning up asbestos-containing soils. "You can see the asbestos in the rock, you can see the fibers," said Roy Zimmerman, a 12-year resident of SloDusty Road, so named by homeowners to capture its dusty, easygoing character.
What's new about the most recent study is that scientists measured airborne asbestos after paving the road with inexpensive chip seal. Tarring the road knocked down airborne asbestos concentrations by 93 percent to 98 percent.
"The measures that we are recommending are resurfacing as soon as you possibly can and until then to drive slower so (as much) dust isn't generated," said Fran Collier, an agency associate toxicologist who worked on the study.
"I think it's quite manageable," said Jim Tjosvolg, DTSC's chief for statewide cleanup operations. "It is a consideration for people who live up there or are considering living up there."
Over the years, California officials have supplied estimates from more than 400 miles to several thousand miles for the unpaved serpentine road run through the state, mostly on private and federal public lands.
Paving just 700 miles of serpentine roads identified in four northern counties Shasta, Siskyou, Trinity and Del Norte in 1990 was estimated to cost a daunting $40 million to $80 million.
Contact Ian Hoffman firstname.lastname@example.org.