- Week of July 8, 2006; Vol. 170, No. 2 , p. 26
Asbestos laces many residential soils
It was the mid-1980s, and Terry Trent and his wife, Carol Adams, had broken ground for their dream home. Atop a hill east of Sacramento, Calif., the remote, 10-acre site in the Sierra foothills offered plenty of privacy. As the couple eventually learned, it offered plenty of something else as well: a nasty type of asbestos known as tremolite. Respiratory exposure to this mineral has been linked with mesothelioma, a lung cancer that quickly turns fatal.
Trent vividly recalls his first encounter with the asbestos. He was working on what would become his front yard. "Operating a backhoe, I popped a roughly 12-inch diameter vein of tremolite out of the ground that was maybe 35 feet long. I thought it was some old, ancient tree root," he told Science News.
Closer inspection revealed a fibrous mat resembling the asbestos that Trent had seen on insulation pads in his college chemistry class. Gently, he reburied the rope. His worries mounted after he turned up smaller ropes of the material throughout the rest of his property. Eventually, Trent found it poking through the surface in so many places that he decided to haul in 1,000 tons of clean-fill dirt to resurface his homestead.
This solution seemed adequate for 9 years—until construction began on the plot next to his. Thick dust regularly covered surfaces inside Trent and Adams' home. The local newspaper, the Sacramento Bee, sent out samples of that dust for chemical analysis. It confirmed heavy contamination with asbestos. Pleas to the owner of the neighboring property and to local officials went for naught, and Trent and Adams' insurance company refused to compensate them for the contamination.
Finally, the couple did the unthinkable. In 1998, they abandoned the house, then valued at $650,000.
Meanwhile, as other families moved into the area—the growing suburban county of El Dorado, where home values can now exceed $1 million—government officials tended to downplay any suggestion that the soil was toxic. That is, until last year, when the Environmental Protection Agency told local residents that its data showed worrisome concentrations of the carcinogenic fibers could be kicked up by normal activities.
What's more, federal scientists now observe, El Dorado is hardly unique. Shallow, natural deposits of asbestos occur in 50 of 58 California counties and in 19 other states.
Although some building-industry groups dispute EPA's El Dorado findings, federal scientists have launched a campaign to evaluate threats that such deposits pose to the people living above them.
One problem in documenting any effects of natural asbestos deposits is that those needlelike fibers tend to be bulkier than the asbestos fibers used by industry and so tend not to remain airborne long enough to be captured by outdoor air-pollution monitors.
EPA sent scientists, wearing moon suits and personal monitors at face height, to collect personal-exposure data from the town of El Dorado Hills. Values were compared with the asbestos measurements simultaneously recorded by several stationary devices installed nearby, the day before, to sample air about 1.5 meters above the ground.
Asbestos readings were low as long as the researchers were inactive. However, playing basketball in a park in El Dorado Hills kicked up 3 to 16 times as much asbestos as was in the air recorded by the stationary monitoring devices, according to Arnold Den and his colleagues in EPA's Region 9 office in San Francisco. The asbestos probably came from dirt on the asphalt surface. Playing baseball, hiking, or biking on unpaved dirt released even more asbestos, the researchers found.
During a baseball game, "we put monitors on the bases and pitcher's mound, and they recorded much lower [asbestos] values than monitors on the runners," he says. The most asbestos—60 times what stationary monitors picked up in the area—appeared during digging in a garden, Den notes.
Similar data emerged during motor biking at the Clear Creek Management Area, a recreational site southwest of Sacramento.
Results show that everyday outdoor work and play in these areas create a "personal storm" of asbestos-tainted dust, says Den.
Last winter, the National Stone, Sand, and Gravel Association of Alexandria, Va., voiced strong objections to EPA's findings. Although the association doesn't represent home owners or builders, its members' products sometimes contain minerals that come in both asbestos and nonasbestos forms. Association spokesman Gus Edwards says, "Our concern is that any federal regulatory agency ... use sound science to differentiate between [them]."
The industry association hired a consulting firm to evaluate how EPA measured and identified asbestos in El Dorado County. Last November, the R.J. Lee Group, headquartered in Monroeville, Pa., reported that 63 percent of the dust fibers that EPA had termed asbestos in El Dorado Hills didn't meet physical and chemical criteria set by academic mineralogists and that the remaining 37 percent were largely inoffensive rock dust.
In some cases, the fibers' chemical makeup didn't qualify as asbestos, the Lee Group said. In other cases, it charged, EPA inappropriately counted needlelike fragments that had broken off a crystal that was too big to qualify as asbestos. Those fragments aren't asbestos even if they have the same chemistry and dimensions as those that crystallized as asbestos needles, the group said.
Arthur M. Langer, a consulting mineralogist formerly of Brooklyn College, agrees. "There are data by the bucketful" indicating that such cleavage fragments, as they're called, "are, for the most part, inactive," he says.
On April 20, EPA issued a point-by-point rebuttal to the Lee Group's report. "What we did—and Lee attacks us on—is use the public health definition [of asbestos]" rather than the Occupational Safety and Health Administration (OSHA) criteria (see "What's in a Name?" below), says Daniel Meer of EPA's Region 9. In other words, he explains, EPA counted as asbestos both the mineral fibers regulated by OSHA and additional fibers that EPA toxicologists expect to behave similarly in the body. "In the absence of evidence to the contrary," he says, "we will assume the human body can't tell the difference."
Skeptics in the rock-and-gravel industry have pointed out that no formal study has established that people living over diffuse U.S. deposits of asbestos or related fibers are acquiring potentially toxic doses. However, at least three preliminary pieces of evidence suggest risks to people living near asbestos deposits in El Dorado County and elsewhere.
In one informal study, an El Dorado County veterinarian collected lung tissue from two dogs and a cat that had lived in the region for 2 to 9 years and died from causes unrelated to lung disease. The vet also took lung samples from a cat that had lived elsewhere. The specimens were independently analyzed by pathologists Jerrold L. Abraham of the State University of New York Upstate Medical University in Syracuse and Bruce W. Case of McGill University in Montreal.
At the American Thoracic Society meeting last year, Abraham and Case, specialists in asbestos analyses, reported finding up to 9 million asbestos fibers per gram of tissue in the El Dorado County animals' lungs. Those concentrations were higher than those seen in livestock from an area in Europe where tremolite-tainted soil has been linked to human mesotheliomas, according to Abraham. In contrast, tissue from the cat outside the area didn't show any asbestos.
A second indicator of lung effects comes from Mark Germine, a psychiatrist in Mount Shasta, Calif., who before entering medical school was a mineralogist specializing in asbestos. In 1998, he collected soil samples at six sites in El Dorado County. "I found some very loose, hairy stuff—tremolite asbestos," Germine recalls. "Although I was really careful, I didn't wear a respirator," he notes.
The following morning, he coughed up green mucus, indicative of lung inflammation. On a whim, he sent some of the mucus to Abraham, who found it loaded with tremolite. Three months later, Germine washed out his larynx with distilled water. Under a transmission-electron microscope, the rinse water "was loaded with tremolite fibers—more than I could count," he told Science News. He wishes that he'd used a respirator. "I'd never go back there without one," he says.
Finally, a team led by pulmonary physician Marc B. Schenker of the University of California, Davis collected data on 3,000 mesothelioma patients in their state and 890 men with prostate cancer, a malignancy not known to be related to asbestos. In the Oct. 15, 2005 American Journal of Respiratory and Critical Care Medicine, the team reported that although most mesotheliomas occurred in people who had worked with asbestos, people who simply lived near known deposits of rock likely to include asbestos also had an elevated incidence of the lung cancer but not prostate cancer. Indeed, risk of mesothelioma steadily declined by 6 percent for every 10 kilometers that an individual had lived from a likely asbestos source.
Living with asbestos
Many government officials say that it's possible to coexist safely with asbestos-tainted soils. Some physicians and mineralogists doubt it.
Since EPA officials reported on asbestos-laden dust in El Dorado Hills last year, the county government has enacted new controls on dust from construction sites. Home sellers must now disclose the presence of asbestos in their soil, where known.
Two decades ago, scientists discovered that large portions of Fairfax County, Va., also were underlain with tremolite. With housing under development throughout much of the affected 28-square-kilometer area, the county quickly developed laws to monitor for asbestos in construction dust and to control soil taken from the area, notes John Yetman, an official with the program. As new buildings are erected at affected sites, the surface must be capped with 6 inches of clean, stable material, such as dirt, sod, or asphalt. Fairfax's rules have gained national renown.
But the county doesn't publicize its asbestos problem, and home sellers don't have to alert buyers about near-surface tremolite, says Yetman. The county does host a Web site ( http://www.fairfaxcounty.gov/hd/asbintro.htm ) that maps affected areas.
Communities are reluctant to acknowledge the presence of asbestos, says John Puffer, an asbestos researcher at Rutgers University in Newark, N.J. Several years ago, he identified a deposit of blue fibrous crocidolite—a highly toxic form of asbestos—adjacent to a nature trail in Mendham, N.J. "When I pointed it out to the mayor, I expected he would be grateful," says Puffer. Instead, the mayor "went ballistic and basically chased me out of town."
The federal government, however, has begun taking seriously community asbestos problems. Bradley S. Van Gosen of the U.S. Geological Survey in Denver spent a year compiling the accounts up to 100 years old of asbestos deposits in the eastern United States. Last year, he produced a map of 331 asbestos deposits—some so rich they were once mined—running in a band from Alabama to Vermont ( http://pubs.usgs.gov/of/2005/1189/pdf/Plate.pdf ). He's now at work on similar maps for the Midwest and West.
At EPA's behest, Van Gosen is also looking into El Dorado County. He and his colleague Greg Meeker plan to describe the chemistry, shape, and size of fibers from samples they collected there.
Three years ago, El Dorado Hills asked the federal Agency for Toxic Substances and Disease Registry in Atlanta for guidance on evaluating risks posed by the asbestos unearthed during construction of a high school soccer field. The agency determined that some student athletes, coaches, and school workers had received substantial exposures and that the inside of the school needed to be cleaned of asbestos dust, says John Wheeler, an environmental health scientist with the agency.
His office still hasn't yet decided how to address the bigger question of long-term risks from low-level exposures to community asbestos deposits, says Wheeler. The agency is considering setting up a registry to follow the health of residents in El Dorado Hills and perhaps do autopsy studies in the area. Other periodic tests for asbestos are also being considered.
"I think, in general, we've found that [naturally occurring asbestos] is something that you can live with," says Wheeler. People need to be cautious where it occurs—keeping their homes clean, for example, and limiting dusty activities such as tilling the garden.
Abraham is less sanguine about the safety of residential areas overlying natural asbestos deposits. Indeed, he predicts of places such as El Dorado Hills, "It's only a matter of time until we find mesotheliomas there."
What's in a Name?
Asbestos definitions can depend upon whom you consult
Asbestos is a term used to describe any of more than a dozen fibrous minerals. Despite a long history of commercial use and regulation, controversy still simmers over which fibers constitute true asbestos.
There's agreement that two distinct families of the mineral exist. Most deposits underlying U.S. communities contain chrysotile, the type generally regarded as the least toxic. All others, including tremolite, fall into a family known as amphibole asbestos. Differences between families trace to their chemical recipes.
The Occupational Safety and Health Administration (OSHA), the first agency to regulate asbestos, rigidly defines the mineral by the fibers' length, width, and length-to-width ratio. OSHA's rules, however, cover only chrysotile and five amphiboles, including tremolite.
It's not that those six fibers are the only toxic asbestos types, says Jerelean Johnson, who assesses potential asbestos hazards for EPA's Region 9, out of San Francisco. It's that when OSHA established its rules, "they were the only ones widely mined and used commercially," she says.
Fibers of a different size or makeup may be as toxic as the ones that OSHA regulates, says Daniel Meer of EPA's Region 9. Therefore, a public-health definition of asbestos has developed to include fibers not covered by OSHA.
Consider the asbestos contamination at the vermiculite mine near Libby, Mont. An epidemic of lung cancer and other disease (SN: 7/12/03, p. 21: Available to subscribers at http://www.sciencenews.org/articles/20030712/fob4.asp; 6/17/06, p. 372: Available to subscribers at http://www.sciencenews.org/articles/20060617/fob4.asp) developed among miners and townspeople. At least 200 of the area's 8,000 inhabitants died from, and another 1,500 were made ill by, lung diseases initially attributed to tremolite asbestos.
However, when mineralogist Greg Meeker of the U.S. Geological Survey in Denver and his colleagues examined asbestos in Libby ore, they found that only 6 percent was tremolite. Some 80 percent was a chemically similar winchite, and most of the remainder a related richterite.
Although neither winchite nor richterite constitutes asbestos by OSHA's definition, Meer notes that the public health community classifies them as such, because of the evidence from Libby and elsewhere that they trigger asbestos diseases.