U.S. EPA to revisit asbestos toxicity
Just how toxic is amphibole asbestos? That's a question EPA needs to answer for Libby, Mont., and other sites.
After 7 years of work and more than $100 million, the U.S. EPA can not verify the effectiveness of its efforts to clean up amphibole asbestos contamination in Libby, Mont., according to an EPA Office of Inspector General (OIG) report released in December 2006.
Libby is a small town in northwestern Montana, where the mining of vermiculite contaminated by amphibole asbestos led to dire health consequences. Regional doctors report hundreds of deaths and thousands of people sick with respiratory diseases linked to amphibole asbestos exposure. At least 29 cases of mesothelioma, an aggressive, fatal, and rare form of cancer, have also been reported, according to a preliminary analysis by Bruce Case of McGill University (Lung Cancer 2006, 54, S10).
Emergency cleanup coordinator Paul Peronard acknowledges that he can’t say whether the cleanups have been sufficient. “We’ve cleaned over 700 homes, doing the worst first,” he says. For active outdoor areas like gardens and play areas, EPA replaces soil if fibers are observed with a phase contrast optical microscope, which detects fibers at concentrations greater than approximately 0.2% by weight. But amphibole asbestos can present a hazard even at concentrations as low as 0.01%.
In 2005, Peronard resampled activity areas that had not been remediated because fibers were initially undetectable. He got the results in 2006 and, “they are not particularly comforting,” he says. When the passed-over areas were disturbed and sampled, fiber concentrations in the air were 2 orders of magnitude greater than samples taken over clean fill.
Libby’s uncertainty is at the center of a question that has long vexed EPA—the health risk from low-level exposure to amphibole asbestos.
The most common, best-known, and, thanks to thousands of lawsuits, most notorious form of asbestos is chrysotile, formerly used as insulation and currently used in automobile brakes. Yet, for more than a decade, scientists have suspected that amphibole asbestos, which is much less common, is much more deadly. Recent work has confirmed these suspicions, according to Wayne Berman, an environmental scientist who currently heads Aeolus Consulting in Albany, Calif. In contrast, EPA’s out-of-date official assessment of asbestos toxicity, completed in 1986, considers all asbestos fibers to be equally hazardous.
Epidemiology studies show a wide range of potencies for asbestos. This could mean asbestos potency is a function of both fiber size and mineral type, according to Berman, who was funded by EPA for several years to develop a new risk protocol that accounts for these effects.
Because different techniques for counting asbestos fibers, for example, using a phase contrast optical microscope instead of a more powerful electron microscope, produce different results, Berman proposed a standard electron microscopy method for counting and describing fibers.
Then he collaborated with scientists who had studied the effects of asbestos dusts on animals. They used the new standard method to reanalyze the dusts. Berman and statistician Kenny Crump then worked together to identify the sizes and types of fibers that best predicted the numbers of tumors observed in the animal studies.
Berman and Crump finally tested the validity of their analysis by applying it to epidemiology studies of humans sickened by asbestos. The new model substantially improved agreement across these studies.
In February 2003, an EPA expert peer-review panel endorsed the Berman–Crump analysis and unanimously agreed that the carcinogenic potency of amphibole asbestos fibers is at least 2 orders of magnitude greater than that of chrysotile fibers. For a set of Libby samples evaluated by EPA, the Berman–Crump method estimates risk to be about 6–12 times higher than the current official EPA method.
This finding is very robust, according to Health Canada scientist Michael Camus, who notes that an independent study by U.K. Health Inspectorate scientists John Hodgson and Andrew Darnton comes to very similar conclusions.
But almost 4 years later, EPA has not updated its toxicity assessment or conducted a risk assessment for Libby. EPA’s science adviser Steven Foster says, “Although our results suggest that amphibole asbestos may be more potent than chrysotile asbestos (especially for mesothelioma), it is premature to make quantitative statements about the magnitude of the relative potency.” The agency is getting set to convene another scientific panel to evaluate the issue.
Observers say that the Berman–Crump conclusion is a political hot potato and that EPA lacked the will to follow the science. Asbestos lawsuits could be undermined because risk estimates could shrink. Risk estimates would climb for other amphibole asbestos sites such as El Dorado, Calif. “No one at EPA wanted to face the heat on this, so the project stalled,” says one insider who requested anonymity.
