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Diesel Study Results Present New Challenge

By James Sharpe

The long-awaited results of the federal government’s Diesel Exhaust in Miners Study (DEMS) are in. They claim an elevated risk of lung cancer exists with elevated exposure to diesel particulate.

Associating lung cancer with diesel exhaust has been made in epidemiological studies previously, so on the surface, the latest research merely confirms what numerous scientists have been suggesting for some time. Nonetheless, the latest findings stand out and, as such, are expected to influence upcoming decisions by important public health agencies in this country and abroad.

The reason the DEMS is important is that it was specifically designed to account for shortcomings in the earlier research, particularly to overcome the absence of quantitative measures of exposure. The DEMS was structured to account for other past weaknesses, too. They included small sample size, a latency period too short to account for the long lapse between exposure and onset of cancer, and other potentially influencing factors because they, too, cause lung cancer or are believed to cause it. Chief among these so-called confounders is smoking.

A total of 12,315 study participants were drawn from eight non-metal mines. They were a limestone mine in Missouri, three New Mexico potash operations, an Ohio salt mine, and three Wyoming trona operations. The DEMS included an exposure assessment, a study of the entire group of study participants, and an evaluation in which 198 lung cancer cases from the study group were matched against 598 participants from the group who did not have lung cancer.

This year, two respected public health organizations will reconsider the cancer-causing potential of diesel exhaust and are expected to give the DEMS considerable weight during their evaluative process. They are the International Agency for Research on Cancer (IARC) and the U.S. National Toxicology Program (NTP). They previously designated diesel exhaust as probably carcinogenic in humans or as reasonably likely to be a human carcinogen, respectively. Reviewers will be looking to see if diesel exhaust should be branded a known human carcinogen.

Although mining companies cooperated with the research, a coalition of mining firms – the Mining Awareness Resource Group (MARG) ‒ has engaged in a long-running face-off against the two research institutes involved, NIOSH and the National Cancer Institute. MARG’s efforts surely succeeded in stretching out the research, since the study took 20 years to complete from an original estimate of seven years. Some believe MARG’s original intent was to forestall a diesel particulate health rule in mining. If so, the effort failed; MSHA issued a final rule in January 2001 that has held up in the face of court challenges over time.

MARG’s engagement may have produced another result as well. Because researchers were well aware that MARG lawyers and scientists were looking over their collective shoulders, the outcome may be a better product as a result of its oversight.

The coalition has also pledged to use “independent” experts to review the research. If there are limitations to or weaknesses in the study, these experts are sure to find them. And, should those problems prove to be material to the findings, those deficiencies also are likely to be considered by the IARC and NTP reviewers. Thus, MARG experts’ critique could be another valuable contribution to the science.

Our bet, though, is that MARG will not be able to undue the central finding of a diesel particulate-lung cancer link. The result is likely to be increased calls for tighter air emissions in dense urban environments and occupational settings and more lawsuits. The findings will provide more ammunition to individuals and groups opposed to nearby industrial operations and to NIMBYs during permit negotiations.

The good news is that we don’t see MSHA acting to strengthen its existing diesel rule, although there is a distant possibility the agency will try and reduce the permissible exposure limit under cover of extending its regulation to surface operations, something organized labor has sought since the beginning.

Tort lawyers turned asbestos into the largest and longest-running tort liability issue in U.S. history. They tried to do the same with silica but have so far failed. Diesel exhaust could be next. It is time to gird for what may be coming.