A major new federal study shows that New Mexico's 1,000 underground miners face increased cancer risks from exposure to diesel exhaust—and that existing exhaust limits may not be enough to protect them. But thanks largely to a little-known industry group called MARG, little if anything is likely to come of this new information.

It took nearly 20 years and $11.5 million for the US government to complete its Diesel Exhaust in Miners Study (DEMS) of underground miners in southern New Mexico, Wyoming, Ohio and Missouri.

Researchers from the US National Cancer Institute and National Institute for Occupational Safety and Health found significant elevations in esophageal cancer, lung cancer and pneumoconiosis ("black lung") among diesel-exhaust-exposed workers. The findings could have important legal implications for the mining industry, which has relied on diesel equipment since the 1950s.

Underground miners suffer some of the highest diesel exhaust exposures in the US, George Washington University occupational health researcher Celeste Monforton says. DEMS indicates that almost all underground miners breathe some diesel exhaust, although exposure levels over careers can vary dramatically, depending on the miners' jobs within the mines.

DEMS was the first study to control for US miners' smoking histories and to estimate their exposures to diesel exhaust over the course of more than a decade. The study measured diesel exposures in potash, limestone and salt mines to control for carcinogens, like coal dust and radon, known to occur in coal and metal-ore mines. Among the study's 12,315 miners, those exposed to diesel exhaust faced a three-fold increase in lung cancer overall, and even those with relatively low levels of diesel exhaust exposure (similar to those found in urban areas such as Los Angeles or Mexico City) saw a 50 percent increase in lung cancers.

In New Mexico, DEMS identified 102 exhaust-exposed miners with lung cancer out of a total of 8,356 current and former potash miners included in the study. The most heavily exposed potash miners faced three times the lung cancer risk of unexposed surface workers.

Jimmie Simpson, who worked at Mosaic's potash mine in Carlsbad for 38 years, participated in DEMS—and now knows he's lucky to have been a surface facility worker rather than an underground miner.

"They gave us the [DEMS] questionnaire years ago," Simpson says. "They sent me my results just a few weeks ago. They were good!"

Although the US Mine Safety and Health Administration does regulate diesel exhaust exposure in underground mines, DEMS makes clear that stricter regulation may be necessary. Monforton says states have the authority to adopt stricter regulations, but New Mexico currently doesn't, state Bureau of Mine Safety Director Fernando Martinez tells SFR. Asked if the state might study stricter diesel rules for underground mines in light of the new data, Jim Winchester, the spokesman for the Energy, Minerals and Natural Resources Department, says the state does not set such regulations and referred SFR to MSHA.

MSHA, however, has had an uphill battle for diesel exhaust regulation. The agency first tried, in 2001, to limit mines' ambient levels of particulate matter (carbon) from diesel exhaust. But for more than a decade, a Washington, DC-based industry group called the Methane Awareness Resource Group (MARG) Diesel Coalition fought strict limits as economically infeasible, Monforton says—and by law, MSHA cannot impose regulations deemed infeasible for industry.

Since the mid-1990s, when MARG wasn't busy delaying diesel-exposure limits, the group was filing lawsuits and lobbying Congress to slow completion and publication of DEMS. In 2011, MARG reported spending $120,000 on lobbying federal lawmakers—not including what it spent suing MSHA and other federal agencies to halt the study and regulation of diesel exhaust in mines.

In 2008, MSHA finally announced air quality regulations that cap diesel exhaust levels at 160 micrograms per cubic meter of air.

"[One hundred sixty] is still high, and it has nothing to do with whether workers are safe," Monforton says. "It's just the legally required limit now. Whether it's protective of workers is another question."

A truly protective regulation would likely cap diesel exhaust exposures at less than half the current limit, the DEMS data suggest—at 57 micrograms or less.

By that measure, diesel exhaust levels at New Mexico mines, while improving, may be far from safe.

MSHA air quality data show that diesel exhaust exposures in Mosaic's Carlsbad mine have dropped from a high of 341.96 micrograms per square meter of air in 2003 to 131 micrograms in September 2009 (the most recent inspection during which MSHA tested for diesel exhaust)—a 62 percent reduction. In 2007, however, MSHA cited Mosaic for a diesel exhaust violation involving a 414 micrograms finding, agency records show.
Intrepid Potash, which operates the state's two other active potash mines, has made more substantial progress, reducing diesel exhaust levels in one mine by 90 percent between 2003 and 2010.

After fighting MARG for years to get the existing limit in place, Monforton says, MSHA is unlikely to try to strengthen exposure limits again—even in light of the DEMS findings.

"MSHA doesn't issue a lot of regulations," Monforton says. "They're trying to work on silicosis and black lung rules now. At least we have a diesel rule on the books."

MSHA spokeswoman Amy Louviere, who tells SFR that her agency is currently reviewing DEMS in detail, says it reinforces the existing rule.

But some New Mexico lawmakers still have concerns.

"The safety of workers should always be of the utmost importance," US Rep. Ben Ray Luján, D-NM, writes in an email to SFR. "This study raises serious concerns regarding the health of these miners and deserves careful consideration and further review to ensure the safety of underground miners."

MARG, meanwhile, has also tried to stop a reassessment of diesel exhaust's carcinogenicity by the World Health Organization's International Agency for Research on Cancer, critics say. IARC is scheduled to release its findings this June; if it determines that diesel exhaust is a "known," rather than suspected, human carcinogen, mining companies will face lawsuits over avoidable workplace-associated cancers.

This February, MARG made a last-ditch effort to slow publication of DEMS findings, writing to at least four scientific journals' editors to threaten unspecified "consequences" should the journals publish (or even send out for peer-review) papers reporting the study's findings.

That drew a fierce response from scientists, who saw it as an attempt to keep DEMS data out of IARC's review.

But on March 2, despite MARG's threats, the Journal of the National Cancer Institute published the DEMS findings.

A few weeks later, National Cancer Institute sent Simpson his data from the study. "It was good," he says, clearly relieved.

But Monforton still has concerns about the other miners—those, unlike Simpson, who work underground day in and day out.

"Some companies that form these coalitions like MARG—in my opinion, they're the ones that would rather spend money paying lawyers to fight regulations than taking those funds and making changes to protect their workers," she says. "I've often wondered, if they were to feed a pipe from the mines into [MARG attorney] Henry Chajet's office in DC, and he had to breathe the crap the miners are breathing, if he wouldn't change his mind."

Full disclosure: Bryant Furlow is a US correspondent for The Lancet Oncology, one of the medical journals that received MARG's 2012 letter discouraging editors from publishing DEMS findings. He reported in February on MARG's threats to medical journals in The Lancet Oncology.

Further Reading:

Celeste Monforton. "Weight of the Evidence or Wait for the Evidence? Protecting Underground Miners from Diesel Particulate Matter." American Journal of Public Health, February 2006; 96(2):271-276.

Debra T Silverman, et al. "The Diesel Exhaust in Miners Study: A Nested Case-Control Study of Lung Cancer and Diesel Exhaust." Journal of the National Cancer Institute, 2012;104:1-14.

Bryant Furlow. "Industry Group 'Threatens' Journals to Delay Publications." The Lancet Oncology.