Diesel exhaust

What is diesel exhaust?

Diesel is a type of fuel derived from crude oil. Large engines, including those used in many trucks, buses, trains, construction and farm equipment, generators, ships, and in some cars, run on diesel fuel.

The exhaust from diesel engines is made up of 2 main parts: gases and soot. Each of these, in turn, is made up of many different substances. The gas portion of diesel exhaust is mostly carbon dioxide, carbon monoxide, nitric oxide, nitrogen dioxide, sulfur oxides, and hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs). The soot (particulate) portion of diesel exhaust is made up of particles such as carbon, organic materials (including PAHs), and traces of metallic compounds. Both the gases and the soot of diesel exhaust contain PAHs.

Exposure to diesel exhaust is widespread in the modern world. Exhaust from diesel engines brings a complex mixture of soot and gases to roadways, cities, farms, and other places. Health concerns about diesel exhaust relate not only to cancer, but also to other health problems such as lung (respiratory) and heart diseases.

How are people exposed to diesel exhaust?

People are exposed to diesel exhaust mainly by breathing in the soot and gases, which then enter the lungs. The amount of diesel exhaust people are exposed to varies greatly. Measuring these exposures is not easy because diesel exhaust is chemically complex and many parts of it are also found in a lot of other sources. This has been, and remains, a major challenge in scientific studies.

People may be exposed to diesel exhaust at work, around the home, or while traveling.

At work

People with the some of highest exposures at work include truck drivers, toll booth workers, miners, forklift drivers, railroad and dock workers, and garage workers and mechanics. Some farm workers may also spend a lot of time around diesel exhaust.

Where you live and play

People can also be exposed to diesel exhaust in areas where they live and play, although typically at lower levels than in the workplace. Exposures are highest where diesel traffic is heaviest, such as along major highways and in cities.

While traveling

Exposure to diesel exhaust may be higher when in a vehicle, especially when traveling on roads with heavier truck or bus traffic. Commuting to and from work is a potential source of diesel exhaust exposure for many people. One particular area of concern is children's exposures to diesel exhaust and other pollutants while riding in school buses, as the buses themselves typically run on diesel fuel.

Does diesel exhaust cause cancer?

Researchers use 2 main types of studies to try to determine if a substance or exposure causes cancer. (A substance that causes cancer or helps cancer grow is called a carcinogen.)

One type of study looks at cancer rates in different groups of people. Such a study might compare the cancer rate in a group exposed to a substance versus the rate in a group not exposed to it, or compare it to what the expected cancer rate would be in the general population. But studies of people can sometimes be hard to interpret, because there may be factors affecting the results that are hard to account for.

In studies in lab animals, other factors are easier to control for, but it's not always clear if the results in animals would be the same in humans.

In most cases neither type of study provides definitive evidence on its own, so researchers usually look at both human and lab-based studies.

Studying a substance like diesel exhaust can be even more complicated because it is actually a mixture of many chemicals. Therefore, researchers have to look at studies of the parts of diesel exhaust, such as soot and PAHs, as well as studies of diesel exhaust itself.

On top of this, changes in diesel technology in recent decades have resulted in lower levels of soot (particles) in diesel exhaust. Studying diesel exhaust exposure from decades ago may not be the same as studying current exposures.

Studies in people

It is not easy to study the possible health effects of diesel exhaust in people. First, it is often very hard to correctly define and measure the level of exposure. It can also be difficult to take into account the impact of other cancer risk factors, such as smoking.

Lung cancer is the major cancer thought to be linked to diesel exhaust. Several studies of workers exposed to diesel exhaust have shown small but significant increases in risk of lung cancer. Men with the heaviest and most prolonged exposures, such as railroad workers, heavy equipment operators, miners, and truck drivers, have been found to have higher lung cancer death rates than unexposed workers. Although most studies have found a link between diesel exhaust exposure and lung cancer, some have not. Still, based on the number of people exposed at work, diesel exhaust may pose a substantial health risk. The relationship between lung cancer and exposure to diesel exhaust outside of the workplace has not been studied extensively.

Several studies have looked for possible links between diesel exhaust and other cancers, including cancers of the larynx (voice box), stomach, and bladder. Studies have also looked for links to blood system cancers such as lymphomas and leukemias (including childhood leukemia). While some studies have found possible links, others have not. More research is needed to determine if diesel exhaust exposure is linked to any of these other cancers.

Studies done in the lab

In studies of cells done in lab dishes, diesel exhaust (as soot or chemical extracts) can cause changes in the cells' DNA. These types of changes are usually necessary for cancer to develop, although not all substances that cause DNA changes also cause cancer.

Several studies have found that long-term, heavy exposure to diesel exhaust can cause lung cancer in lab animals such as rats. However, the cancer-causing effects of diesel exhaust in these animals may relate to soot overload in their lungs. If true, this would suggest that normal lung defenses must be overcome in order for diesel exhaust to cause lung cancer.

What expert agencies say

Several agencies (national and international) study different substances in the environment to determine if they can cause cancer. The American Cancer Society looks to these organizations to evaluate the risks based on evidence from laboratory, animal, and human research studies.

Some of these expert agencies have classified diesel exhaust as to whether it can cause cancer. These classifications are based largely on studies looking at the possible link to lung cancer.

The National Toxicology Program (NTP) is formed from parts of several different US government agencies, including the National Institutes of Health (NIH), the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA). The NTP has classified exposure to diesel exhaust particulates as "reasonably anticipated to be a human carcinogen."

The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO). Its major goal is to identify causes of cancer. Based on the available data, IARC classifies diesel engine exhaust as "probably carcinogenic to humans."

The US Environmental Protection Agency (EPA) maintains the Integrated Risk Information System (IRIS), an electronic database that contains information on human health effects from exposure to various substances in the environment. The EPA classifies diesel exhaust as "likely to be carcinogenic to humans."

The National Institute for Occupational Safety and Health (NIOSH) is part of the CDC that studies exposures in the workplace. NIOSH has determined that diesel exhaust is a "potential occupational carcinogen."

(For more information on the classification systems used by these agencies, see our document, Known and Probable Human Carcinogens.)

Does diesel exhaust cause any other health problems?

Diesel exhaust is a major part of outdoor air pollution. Diesel exhaust is believed to play a role in other health problems, such as eye irritation, headache, asthma and other lung diseases, heart disease, and possibly immune system problems.

Can I reduce my exposure to diesel exhaust?

Diesel exhaust can cause several health problems and can most likely increase lung cancer risk, so it makes sense to lower your exposure to it whenever possible. However, since most human exposure comes from transportation-related diesel exhaust near highways, government regulations may be more effective in limiting exposure than individual choices.

At work

If you are exposed to diesel exhaust at work, there are ways to reduce or prevent exposures. Some of these measures will also protect you from other chemical exposures that are likely to happen in the workplace.

Talk with your employer to be sure that you are protected adequately. Personal protective equipment, such as respirators, may be a key part of a workplace protective program. If needed, engineering changes, such as ventilating the exhaust away from where you breathe, can also be important. Good work practices, such as changing clothes after work, washing hands regularly, and keeping food out of the work area, may be helpful as well.

For more information on preventing or reducing workplace exposures at your job, consult your company's safety and health manager. If needed, you can get additional assistance from the Occupational Safety & Health Administration (OSHA), the government agency responsible for enforcing workplace safety.

Where you live and play

If you are exposed to diesel exhaust fumes in your environment, you can take some of the same precautions. For example, you can avoid spending time near large sources of diesel exhaust, such as near trucks and buses. Commuting to and from work is a potential source of diesel exhaust exposure for many people, whether using car or some type of public transportation. For some people, working from home (telecommuting or teleworking) may be an option to lower their exposure, as well as to save money on commuting expenses.

Government regulations such as the Clean Air Act and programs such as the EPA's National Clean Diesel Campaign are designed to reduce diesel emissions from trucks and other large engines, lowering public exposure to diesel exhaust.

Another important program is Clean School Bus USA. Children can be exposed to diesel exhaust during school bus travel or when standing near running school buses outside of school. Clean School Bus USA brings together partners from business, education, transportation, and public-health organizations to reduce children's exposure to bus-related air pollutants by aiming to:

• Reduce unnecessary school bus idling
• Replace older buses with newer, less-polluting buses
• Upgrade existing buses with technologies to reduce their emissions

Additional resources

More information from your American Cancer Society

We have some related information that may also be helpful to you. These materials may be ordered from our toll-free number, 1-800-227-2345.

Known and Probable Human Carcinogens

National organizations and Web sites

In addition to the American Cancer Society, other sources of information and support include*:

Environmental Protection Agency (EPA)
Web site: www.epa.gov
Clean School Bus USA: www.epa.gov/cleanschoolbus
National Clean Diesel Campaign: www.epa.gov/otaq/diesel/index.htm

National Cancer Institute (NCI)
Toll-free number: 1-800-422-6237 (1-800-4-CANCER)
Web site: www.cancer.gov

National Institute for Occupational Safety and Health (NIOSH)
Toll-free number: 1-800-232-4636 (1-800-CDC-INFO)
Web site: www.cdc.gov/niosh

Occupational Safety & Health Administration (OSHA)
Toll-free number: 1-800-321-6742 (1-800-321-OSHA)
Web site: www.osha.gov
Safety and health topics: diesel exhaust: www.osha.gov/SLTC/dieselexhaust/index.html

No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-227-2345 or visit www.cancer.org.

References

Boffetta P, Stellman SD, Garfinkel L. Diesel exhaust exposure and mortality among males in the American Cancer Society prospective study. Am J Ind Med. 1988;14:403−415.

Environmental Protection Agency. Integrated Risk Information System: Diesel engine exhaust (CASRN N.A.). 2010. Accessed at www.epa.gov/IRIS/subst/0642.htm on March 31, 2010.

Frumkin H, Thun MJ. Diesel exhaust. CA Cancer J Clin. 2001;51:193−198.

Garshick E, Schenker MB, Muñoz A, et al. A case-control study of lung cancer and diesel exhaust exposure in railroad workers. Am Rev Respir Dis. 1987;135:1242−1248.

Garshick E, Schenker MB, Muñoz A, et al. A retrospective cohort study of lung cancer and diesel exhaust exposure in railroad workers. Am Rev Respir Dis. 1988;137:820−825.

Heinrich U, Muhle H, Takenaka S, et al. Chronic effects on the respiratory tract of hamsters, mice, and rats after long-term inhalation of high concentrations of filtered and unfiltered diesel engine emissions. J Appl Toxicol. 1986;6:383−395.

International Agency for Research on Cancer. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol 46: Diesel and Gasoline Engine Exhausts and Some Nitroarenes. 1989. Accessed at http://monographs.iarc.fr/ENG/Monographs/vol46/volume46.pdf on March 31, 2010.

Madden MC. Complex issues with examining diesel exhaust toxicity: is the task getting easier or harder? Exp Toxicol Pathol. 2008;60:135−140.

Mauderly JL, Jones RK, Griffith WC, et al. Diesel exhaust is a pulmonary carcinogen in rats exposed chronically by inhalation. Fundam Appl Toxicol. 1987;9:208−221.

National Institute for Occupational Safety and Health (NIOSH). Current Intelligence Bulletin 50: Carcinogenic Effects of Exposure to Diesel Exhaust. 1988. Accessed at www.cdc.gov/niosh/88116_50.html on March 31, 2010.

Steenland K, Silverman DT, Hornung RW. Case-control study of lung cancer and truck driving in the Teamsters Union. Am J Public Health. 1990;80:670−674.

Steenland K, Silverman DT, Zaebst D. Exposures to diesel exhaust in the trucking industry and possible relationships with lung cancer. Am J Ind Med. 1992;21:887−890.

Steenland K, Deddens J, Stayner L. Diesel exhaust and lung cancer in the trucking industry: Exposure-response analyses and risk assessment. Am J Ind Med. 1998;34:220−228.

US Department of Health and Human Services. Public Health Service, National Toxicology Program. Report on Carcinogens, Eleventh Edition. 2005. Accessed at http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s069dies.pdf on March 31, 2010.