By Scott E. Stewart and Mark Savit

Since the mid-1990s, diesel engine and emission control technology has improved significantly as the Environmental Protection Agency (EPA) has imposed ever-tightening emission control and fuel standards pursuant to its Clean Air Act authority. In its most recent nonroad diesel rulemaking, the EPA estimated that standards imposed for nonroad land-based diesel engines typically used in construction, agricultural, industrial and mining operations will achieve particulate matter (PM) reductions in excess of 95%. As a result of a variety of programs, including access to funding under the Diesel Emissions Reduction Act, the EPA’s National Clean Diesel Campaign is effectively addressing older diesel engine emissions without resorting to new job-killing regulation.

Ironically, against this backdrop, the National Institute for Occupational Safety and Health (NIOSH) and the National Cancer Institute (NCI),1 released the Diesel Exhaust in Miners Study (DEMS) in 2012, a deeply flawed and expensive endeavor to examine the potential health effect of diesel exhaust exposure on miners working in nonmetal mines dating back over a half century. NIOSH and NCI concluded that there is an increased risk of lung cancer death as levels of exposure to diesel exhaust increase.  Even after acknowledging that the data from the study are not sufficient to estimate the risk of low level diesel exhaust exposure on the general population, the NCI press release asserts the DEMS findings “suggest that the risks may extend to other workers exposed to diesel exhaust in the U.S. and abroad, and to people living in urban areas where diesel exhaust levels are elevated.”
Although NIOSH and NCI attempted to eliminate certain confounding factors by focusing on nonmetal mines, the DEMS does not adequately address other confounding factors including how cigarette smoke and non-diesel airborne pollutants impact workers’ cancer risks, the use of carbon monoxide and horsepower as surrogates for diesel exhaust, and modeling 1998-2001 air survey data to the 1947-1997 study period where no actual diesel air monitoring data existed. A particularly glaring issue is that the DEMS concludes the risk of lung cancer tapered off for heavy smokers in the highest exhaust exposure group. The science has been called into question and the process undertaken by the DEMS researchers has been opaque. Even in the face of congressional demands, NIOSH and NCI have failed to disclose data and analysis relied upon for the DEMS conclusions.  
The ripple effect from this deeply flawed study, which methods and analysis were developed behind closed doors and away from public scrutiny, is already being felt both nationally and internationally.   

On June 12, 2012, the International Agency for Research on Cancer (IARC), part of the United Nation’s World Health Organization, upgraded its diesel exhaust classification to “carcinogenic to humans,” citing DEMS. Although IARC claims its evaluations do not directly recommend legislation or regulation, it recognizes the evaluations are designed to be used by national and international health and environmental regulatory authorities in “making their risk assessments and taking preventative action.” In fact, in the United States, IARC findings are much more powerful. Although not subject to notice and comment rulemaking or other standard public scrutiny, nor related to current diesel engine clean technology, IARC findings directly affect companies’ Hazard Communication Reporting responsibilities.  Manufacturers, importers and employers are required to treat IARC findings as a source “establishing that a chemical is a carcinogen…for hazard communication purposes.” 29 C.F.R. §1910.1200(d)(4).  

In addition to current and potential regulatory burdens associated with revising MSDSs, IARC’s reliance on the DEMS creates “evidence” that may be used by plaintiffs’ lawyers. The first such lawsuit relying on the IARC finding, and the DEMS study that informed it, was filed in a California court against three of the world’s largest integrated petroleum companies on June 13, 2012. A wave of similar lawsuits could follow against other industries reliant on diesel power. We can also expect that environmental activists will use the DEMS and IARC to bolster their advocacy and lawsuits.

The National Toxicology Program (NTP), also part of HHS, is tasked by Congress to compile and publish biennially the Report on Carcinogens (ROC)—listing all substances which are either “known to be carcinogens or may reasonably be anticipated to be carcinogens.” 42 U.S.C. § 241(b)(4). The next edition of the ROC is under development, due to be published in 2013. In light of IARC’s wholesale acceptance of the flawed DEMS there is a significant risk that the NTP will follow suit. Just as with IARC findings, the ROC is another source that must be used in the U.S. for establishing that a chemical is a carcinogen for hazard communication purposes.
The environmental justice community has long advocated for the EPA to revisit its assessment of risks posed by diesel exhaust. The EPA’s National Air Toxics Assessment (NATA) program is a national-scale assessment program focused on cancer risks and noncancer health effects of a variety of air toxics. Although the program is not designed to characterize risk sufficiently for it to be the sole source for regulatory action, it is used by national, state and local policymakers as a source of information driving regulation. In 2011, the EPA released its most recent NATA. As it had with previous NATAs, the EPA noted that there is a potential cancer risk from diesel PM, but the available data is inadequate to support a quantitative estimate of the carcinogenic potency of diesel PM. In its 2002 Health Assessment Document for Diesel Engine Exhaust, the EPA concluded that diesel exhaust was “likely to be carcinogenic to humans by inhalation,” but because of the uncertainties and assumptions in the studies reviewed, EPA did not believe the evidence supported a quantitative exposure/dose-response relationship.  Environmental justice advocates will certainly use the DEMS as a basis to push EPA to develop a quantitative risk estimate for diesel exhaust. There is significant danger that EPA will embark on this course in future NATAs, thereby furthering the reach of the faulty DEMS.

The conclusions reached in DEMS are, today, far-reaching.  If this deeply flawed study continues to be relied upon by policymakers and advocates, unsound decisions will further muddle efforts to rationally control diesel exhaust emissions.

1    NCI is part of the National Institutes of Health (NIH), which is an agency of the Department of Health and Human Services (HHS).  

Stewart is a partner in Environmental Law practice at Patton Boggs LLP, focusing on environmental litigation and regulatory matters. He may be reached at Savit is a partner in the Denver office of Patton Boggs, LLP. He can be reached at