For more than a decade, the mining industry has been waging a war to cast doubt on scientific studies showing that diesel exhaust causes lung cancer. Industry lost that fight on June 12 when the International Agency for Research on Cancer (IARC) voted unanimously to designate diesel exhaust as a known cause of lung cancer. IARC’s conclusion comes more than a decade after the Mine Safety and Health Administration (MSHA) adopted a standard that reduced miners' exposure to diesel particulate matter – a prudent move on MSHA's part in the face of industry criticism.

On Jan. 19, 2001, the last day of the Clinton administration, MSHA issued a standard regulating miners’ exposure to diesel particulate matter (DPM) in metal and non-metal mines. MSHA’s goal was to protect miners from lung cancer and other respiratory diseases. Mining interests fought MSHA’s standard, claiming the agency was relying on “junk science” and that the rule would cost the mining industry too much money.

Miners who work underground are exposed to extremely high levels of diesel exhaust because diesel engines power the equipment used to extract ore. By the 1990s, dozens of epidemiology studies showed that workers exposed to high levels of diesel particles had a statistically significant increased risk of lung cancer. During the Clinton administration, MSHA proposed to strictly regulate the amount of these particles that miners could be exposed to. In response, the mining industry worked hard to create phony “doubts” about the need for a new diesel standard, and the rule wasn’t finalized before Clinton left office.

When the Bush administration arrived, the mining industry used its new political clout to try to stop the standard. Initially, it looked like they had succeeded: MSHA proposed to weaken and delay the rule. However, in 2006, MSHA reaffirmed the scientific basis for the DPM standard and added medical evaluation and transfer rights for miners who became ill. In response, the industry tried to convince a federal appeals court that MSHA’s rule lacked an adequate basis, but the challenge was rejected.

The industry also tried to undermine federal research on the hazards of diesel exhaust. In the mid-1990s, the National Institute for Occupational Safety and Health (NIOSH) was about to begin an epidemiology study to determine whether DPM caused lung cancer among miners and asked its Board of Scientific Counselors to review the study protocol. Through a clerical error, NIOSH forwarded the charter for this federal advisory committee to the wrong congressional committee, and mining interests used this mistake to argue that they had been “harmed” by this procedural error.

The industry was able to persuade a federal judge in Louisiana, on three different occasions, to enjoin NIOSH from publishing the results of its DPM study until industry representatives had reviewed the research. NIOSH appealed this order three times and, in February 2012, was permitted to publish the final results of its diesel study.

The study was much more comprehensive than earlier research. NIOSH and the National Cancer Institute jointly studied more than 12,000 workers exposed to diesel exhaust. The research determined that miners exposed to DPM faced a three-fold risk of lung cancer. Those with the highest exposures had a five-fold risk of developing the disease compared with the lowest exposed workers.

For 20 years, the International Agency for Research on Cancer (IARC) had designated diesel exhaust as a probable human carcinogen. After NIOSH published the results of its study earlier this year, an IARC study committee unanimously ruled that diesel engine exhaust causes lung cancer in humans. Diesel exhaust is now in the same risk category as asbestos and tobacco.

It turns out that MSHA was right. The agency acted prudently to protect miners and refused to bow to political pressure or the industry campaign to question the quality of the science on which its rule was based. This time, David beat Goliath.

Image in teaser by flickr user marc falardeau, used under a Creative Commons license.