The notion that diesel exhaust can cause the body harm — specifically cancer — hardly seems shocking. The US National Toxicology Program suggests that diesel exhaust particles can be “reasonably anticipated” to be carcinogenic, and the International Agency for Research on Cancer lists them as “probable carcinogens“. The US Mine Safety and Health Administration cited cancer risks when it regulated diesel emissions in mining operations back in 2001.

So it is not entirely surprising that a landmark new study involving US miners has identified sharply higher cancer rates in workers exposed to high levels of diesel exhaust. But the study is more comprehensive and apparently robust than those that have come before, and it comes as at least one major scientific organization prepares to reassess the link between diesel exhaust and cancer. Perhaps it was the fear of this exact scenario that led a coalition of industrial interests to wage a 17-year legal and political battle against government scientists conducting the study — a battle that now appears to have outlived its purpose thanks to a 29 February ruling from the US Fifth Circuit Court of Appeals.

Researchers at the National Cancer Institute (NCI) in Bethesda, Maryland, and the National Institute for Occupational Safety and Health (NIOSH) in Atlanta celebrated the publication of a trio of studies today, including two concluding papers in the Journal of the National Cancer Institute (not affiliated with NCI). Initiated in 1998, after the first of many legal delays, the study analysed exposures in detail for more than 12,000 workers while controlling for smoking and other risk factors; researchers also focused on a series of non-metal mines to minimize the effects on the results of workers’ exposure to radon and other contaminants. In the end, the scientists found that miners faced a three-fold risk of lethal lung cancer, and underground workers who were heavily exposed faced a five-fold risk.

“It’s been a long hard road,” says Debra Silverman, an NCI epidemiologist who has been working on the study since its inception in the early 1990s. “But I’m very happy to see this happen.”

The legal dispute began around 1995, quickly turning a ground-breaking study into a legal and political exercise that ultimately required researchers to release their data before peer review. It’s a long and strange tale, first detailed by the non-profit Center for Public Integrity here, but we’ll skip forward to August 2011. That’s when a US District Court in Louisiana affirmed an earlier ruling granting an industry coalition led by the Mining Awareness Resource Group (listed as the Methane Awareness Resource Group on court documents) as well as the US House Committee on Education and the Workforce the right to a 90-day review of any data be publication.

The court also held the science agencies in contempt of court for apparently failing to provide said data, even as House lawmakers and industry officials had sought access to additional data. As detailed over at ScienceInsider, a law firm representing the Mining Awareness Resource Group even wrote vaguely threatening letters to scientific journals that might publish the studies. An attorney representing the group did not return a phone call from Nature seeking comment.

But the science agencies and their attorneys at the US Department of Justice appealed that ruling and argued that they had already complied and turned over the data. That’s where the matter stood until last week, when the US Court of Appeals stayed the lower court’s August ruling. No final decision has been rendered in the case, and officials at the Cancer Institute and the Justice Department declined to comment. But with the earlier ruling lifted there was nothing to prevent publication. The 90-day deadline expired on 1 March, and today the studies went live.

New assessments

The results come as the International Agency for Research on Cancer, part of the World Health Organization, prepares to reassess the carcinogenic effects of diesel exhaust at a meeting in Lyon, France, this June. Kurt Straif, who heads the unit conducting the review, says that the NCI–NIOSH study is one of the reasons his group is reviewing diesel emissions, but studies on cancer and diesel emissions have come out in recent years. “They all seem to point in the same direction,” Straif says, suggesting some level of increased risk of lung cancer. In the United States, the National Toxicology Program at the Department of Health and Human Services is now considering whether to reassess diesel exhaust as part of its 2013 Report on Carcinogens.

Both are purely scientific bodies, but any upgrade in diesel exhaust’s link with cancer would ripple through the regulatory system as governments consider their rules and requirements. The non-profit Clean Air Task Force is also citing the new research as it makes the case for clean-air provisions in legislation pending on Capitol Hill.

Celeste Monforton, a professorial lecturer at the George Washington University in Washington DC, marvels at how hard the industry has fought this particular study. She suggests this kind of legal wrangling — although perhaps extreme in this case — has itself become an industry in Washington (for more of the sordid history, see her detailed writings here and here). At the same time, harking back to mining regulations instituted by the Clinton administration in 2001 that substantially lowered allowable exposures to diesel exhaust, Monforton says that the mining industry responded by doing simple things like shifting to low-sulphur fuel and installing filters to clean up emissions.

“These are not necessarily high-tech solutions,” she says. “There were feasible controls that they could put in place to try to protect their people, and I think most of the mining operations view it that way.”

Nonetheless, she says a quick analysis of the NCI—NIOSH study suggests that workers might face an elevated risk of lung cancer even under the present regulations, in which case it will be up to regulators to weigh the costs and benefits of more stringent standards. More broadly, the study could provide fodder for calls to expand protections to workers in other settings, such as bus terminals and maintenance depots.

photo: NIOSH/CDC