New and Old Diesel Components Under Scrutiny

Statements by an international agency and recently published research have focused attention on the health and environmental effects of diesel fuel exhaust, opening the door for legal action associated with traditional (pre-1988) exhaust and prompting a closer look at nano-additives in modern, cleaner burning diesel. Recent litigation is related to diesel emissions based on the IARC classification for older technology. New research suggests that one nanotechnology solution to meeting Clean Air Act requirements for diesel exhaust may be affecting plant growth, and EPA is targeting their work on this nano-cerium oxide material. Thus, new technologies are in the sights of EPA and could drive new lawsuits and regulations.

Secondary electron image of soot emissions with a cerium additive. Thorough characterization of cerium nanoparticles can help with assessing possible effects upon human health and the environment.

In June 2012, the International Agency for Research on Cancer (IARC) re-classified diesel engine exhaust as carcinogenic to humans [1]. This classification was based on occupational health studies of workers exposed to high levels of exhaust from diesel fuel from the 1950s through the 1990s [2, 3]. Soon after IARCs announcement of lung cancer risk, engine manufacturers faced a lawsuit from transit workers in New York, and additional claims can be expected against employers in industries that rely on diesel machinery [4]. Note that these studies were based on traditional diesel and improvements in emissions occurred during the studies. The Clean Air Act [5] regulates a wide range of source emissions and also enters prominently in these types of lawsuits.

In addition to the Clean Air Act, overlapping networks of regulations address diesel exhaust. Occupational diesel exhaust exposure regulations are enforced by the Mine Safety and Health Administration (MSHA) and the Occupational Safety and Health Administration (OSHA). MSHA regulates diesel emission exposure for underground miners and requires that diesel fuels be registered with the EPA [6]. The worker exposure is determined by measuring the amount of elemental carbon, a surrogate for diesel particulate measurements, and requires accredited laboratory sampling and analysis. OSHA does not have rules specific to diesel exhaust, but does have standards for components that make up the exhaust. Additionally, OSHA requires manufacturers of diesel fuel to include hazard information about the exhaust in the material safety data sheet [7].

The most encompassing regulation, the Clean Air Act has been responsible for driving improvements in diesel exhaust emissions and technologies since it was first introduced in the early 1970s. One goal has been to reduce the amount of carbon monoxide, hydrocarbons, nitrogen oxides and particulate matter produced by engines. Manufacturers of fuels and fuel additives are responsible under section 211 of the Clean Air Act to register their products with the EPA before putting them on the market. Manufacturers must perform analysis of vapor (pre-use) and exhaust emissions (post-use) and provide the information to the EPA.

Scientists have created a cleaner energy source by introducing cerium nanoparticles to diesel fuels. The nano-cerium acts as a catalyst resulting in decreased particulate matter, or soot, and improved fuel efficiency. However, a small amount of cerium from the fuel is contained in the exhaust and emitted in the environment. A recent study claims that cerium oxide nanoparticles in soil negatively affected soybean growth by interfering with fertilizer-soybean interaction at the roots [8], suggesting that diesel emissions of cerium could be eyed as a potential contributor to variations in growing seasons. A closer look at this study shows its limitations in extending the results to diesel exhaust. Soil concentrations used were orders of magnitude higher than the level of naturally occurring cerium. The nanoparticles used were as-produced from the manufacturer as opposed to those from the exhaust. Fuel-based cerium particles can increase in size and change properties as they go through the combustion process; the extent of the changes depends on the particular engine and internal temperatures [9]. A more relevant study with parameters closer to current day, real-world emissions would increase the knowledge of potential environmental effects.

Science-based understanding of nano-cerium behavior in diesel exhaust is critical to further use of the additive. To this end, the U.S. EPA is working to determine correlations among particle size, particle behavior, and risks to human health and the environment [10, 11]. The emerging potential of environmental claims requires proper determination of the origin of the cerium found in the environment and realistic assessment of its toxicity, which will be critical for product stewardship and compliance.


1. IARC: Diesel Engine Exhaust Carcinogenic, World Health Organization Press Release No. 213, June 12, 2012.

2. Silverman, D.T., C.M. Samanic, J.H. Lubin, A.E. Blair, P.A. Stewart, R. Vermeulen, J.B. Coble,

N Rothman, P.L. Schleiff, W.D. Travis, R.G. Ziegler, S. Wacholder , and M.D. Attfield, The Diesel Exhaust in Miners Study: A Nested Case – Control Study of Lung Cancer and Diesel Exhaust, J. Natl. Cancer Inst, 104: 855-868, June 2012.

3. Attfield, M.D., P.L. Schleiff, J.H. Lubin, A. Blair, P.A. Stewart, R. Vermeulen, J.B. Coble, and D.T. Silverman, The Diesel Exhaust in Miners Study: A Cohort Mortality Study with Emphasis on Lung Cancer, J. Natl. Cancer Inst, 104: 869-883, June 2012.

4. Diesel Exhaust Claims: Stalled or Just Getting Started?, Law360, August 2, 2012.

5. Clean Air Act, EPA,

6. Part II, Diesel Particulate Matter Exposure of Underground Metal and Nonmetal Miners; Final Rule, 30 CFR Part 57, June 6, 2005.

Also see

7. Diesel Exhaust, Occupational Safety and Health Administration,

8. Priester, J.H., R.E. Mielke, A.M. Horst, S.C. Moritz, K. Expinosa, J. Gelb, S.L. Walker, R.M. Nisbet, Y-J., An, J.P. Schimel, R.G. Palmer, J.A. Hernandez-Viezcas, L. Zhao, J.L. Gardea-Torresdey, and P.A. Holden, Soybean Susceptibility to Manufactured Nanomaterials with Evidence for Food Quality and Soil Fertility Interruption, Proceedings of the National Academy of Sciences of the United States of America, August 20, 2012, E2451-E2456.

9. Willis, R., E. Grulke, N. Mandzy, K. Bunker, J.M. Conny, M. Lewandowski, J. Weinstein, J. Krug, K. Kovalcik, and G. Casuccio, Physicochemical Characterization of Cerium Particles Generated by Combustion of Ce-doped Diesel Fuel, Materials Science & Technology Conference, October 2012.

10. Researchers Examine Nanoparticles’ Impact on Fuel Emissions and Air Pollution, Research in Action, U.S. EPA, Accessed October 12, 2012.

11. Exploring Nano-sized Fuel Additives: EPA Scientists Examine Nanoparticle Impacts on Vehicle Emissions and Air Pollution, EPA Science Matters Newsletter, March/April 2011.

Kristin L. Bunker, Ph.D.

About Kristin L. Bunker, Ph.D.

Kristin L. Bunker, Ph.D. in Materials Science and Engineering, is currently a Senior Scientist at RJ Lee Group, Inc. where she specializes in the analysis and characterization of materials utilizing ultra high-resolution electron microscopy and X-ray spectroscopy techniques. She directs and conducts forensic examinations of particulate, nanomaterials, coatings, and thin films in advanced materials, environmental, manufacturing, and pharmaceutical projects. Dr. Bunker works closely with industry, national laboratories, and government agencies in the evaluation of nanoparticles from an industrial hygiene and environmental perspective. She is an expert in the characterization of various nanomaterials used in sensors, diagnostics, aerospace composites, architectural products and protective coatings among others.  
In 2012 Dr. Bunker became the President of the internationally recognized Microanalysis Society (MAS). She is the author or co-author of more than 40 publications covering topics in semiconductors, life sciences, mineralogy, and nanomaterials. Prior to receiving her Ph.D., Dr. Bunker served as an expert witness in California courts for the analysis of Gunshot Residue (GSR).

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