Letter Regarding Threat of Diesel Emissions

November 22, 2000

Alexis M. Herman
U.S. Department of Labor
200 Constitution Ave, NW
Washington, DC 20210

Dear Secretary Herman:

Diesel emissions from heavy machinery represent a well-documented threat of lung cancer to American workers, particularly those working in underground coal, metal and nonmetal mines. In 1992, the Mine Safety and Health Administration (MSHA) published an Advance Notice of Proposed Rulemaking significantly lowering permissible exposures to diesel particulate matter (DPM) and followed this with a Proposed Rule for coal mining on April 9, 1998 and for underground metal and nonmetal mining on October 29, 1998. Unaccountably, more than two years have been allowed to pass without the rule being finalized, despite an urgent request from MSHA to you three months ago on August 10 that the Department of Labor approve the final regulations. We urge that you immediately publish these critical regulations. MSHA's own risk assessment suggests that a reduction from current exposure levels to 200 micrograms/m3 (somewhat above those proposed in the underground metal and nonmetal mining rule, 160 micrograms/m3), would prevent 412 to 8,261 lung cancer deaths among coal miners and 636 to 11,444 lung cancer deaths among metal and nonmetal miners, during a 45-year working lifetime of exposure at current levels. Clearly, the lives of hundreds, and probably thousands, of workers hang on your decision.

These are risks over and above those due to smoking. MSHA's risk assessment indicates that these miners are at a risk for lung cancer that rivals that for heavy smokers, even though many do not smoke. The difference, of course, is that these workers are being exposed involuntarily to these deadly risks. Every day that you fail to act is another day that American miners are left at grave risk of preventable death.

A long series of studies conclusively demonstrate the potential of DPM to cause lung cancer. In its proposed rule for underground metal and nonmetal miners, MSHA reviewed the then-available studies exhaustively. The agency identified a total of 43 epidemiologic studies dating back to 1957 which had examined the risk of lung cancer among people exposed to DPM on the job (usually miners, railroad workers or truck drivers). Of the 43 studies, 38 showed some association between DPM and lung cancer; this finding was statistically significant in 24 studies. The remaining five studies showed some negative association between DPM and lung cancer, but none reached statistical significance. The agency identified two meta-analyses, which analyze and statistically combine the results of all the studies. These found statistically significantly increased risks of lung cancer among DPM-exposed workers of 30%-40%. Importantly, the studies reviewed by MSHA found elevated lung cancer risks at DPM levels substantially below current exposures in U.S. mines and even at levels below those proposed by MSHA for underground metal and nonmetal mining. (Technical factors make it difficult to lower DPM levels much further than the proposed 160 micrograms/m3. The agency is not proposing a specific exposure limit for coal mining due to difficulty distinguishing the carbon in coal from that in DPM, but is instead proposing work practice controls that will substantially reduce worker exposure for that sector. MSHA is also not proposing to regulate DPM in surface mining of any type.)

Leading institutions in carcinogenesis have also concluded that DPM cause lung cancer. The International Agency for Research on Cancer and the World Health Organization have concluded that diesel exhaust is probably carcinogenic in humans and the National Toxicology Program has stated that diesel exhaust is known to be a human carcinogen. As long ago as 1988, the National Institute for Occupational Safety and Health recommended that DPM be regarded as a probable or potential human carcinogen.

Moreover, new studies published since the Proposed Rules make the case for the carcinogenicity of DPM still stronger. A pooled analysis of two case-control studies by Bruske-Hohlfeld, et al. showed that the excess risk of lung cancer for all DPM-exposed workers was 43% (Am J Ind Med 1999;36:405-14). In a smaller study of potash miners by Saverin, et al., those with the highest levels of DPM exposure were at 70% increased risk of lung cancer compared with those with the lowest levels of DPM exposure, but the finding did not reach statistical significance (Am J Ind Med 1999;36:415-22). Gustavsson, et al. used a population-based approach for all 40-75-year-old males with lung cancer between 1985 and 1990, who were compared to matching controls. Those in the highest quartile of cumulative diesel exhaust exposure were 65% more likely to be diagnosed with lung cancer, comparable to the excess risk among those in the highest quartile of cumulative asbestos exposure (Am J Epi 2000;152:32-40). The most recent study, by Larkin, et al., involved over 55,000 railroad workers and showed an excess risk of 44% for those with the longest history of exposure (Am J Ind Med 2000;38:399-409). All studies adjusted for smoking.

The agency has also conducted a peer-reviewed risk assessment that demonstrated the feasibility of the measures it has proposed. Total annual costs to the estimated 200 metal and non-metal underground mines employing 18,700 exposed workers were a very modest $19.2 million, an average of about $100,000 per mine. For the estimated 150 underground coal mines employing 14,700 exposed workers, the annual costs were still lower as diesel engines are less intensively used in that sector. Depending on the level of exposure and the estimate of risk assumed, the excess risk of lung cancer (compared to no exposure to DPM), based on a working lifetime exposure to DPM, was 15 to 800 per 1,000 workers. This means that as many as 80% of workers so exposed could die from lung cancer at a result of DPM exposure. These risks are considerably greater than the 1 per 1,000 worker excess risk standard established in the benzene case as a threshold for government regulation.

The agency has established a clear and convincing record demonstrating the need for regulating this serious occupational hazard. It is time for you to finalize the Proposed Rule before it is too late for too many workers.

Yours sincerely,

Peter Lurie, M.D., M.P.H.
Deputy Director

Sidney M. Wolfe, M.D.
Public Citizen's Health Research Group