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DIESEL EXHAUST EXPOSURE PATHWAYS
Diesel exhaust particles and gases are suspended in the air, so exposure to this pollutant occurs whenever a person breathes air that contains these substances. Although diesel exhaust most easily enters the body by breathing, there are some occupations where the exhaust may cling to skin or hair and there after possibly be ingested as a consequence of hand-to-mouth activity. By far, the major exposure pathway is from breathing.
The prevalence of diesel-powered engines makes it almost impossible to avoid exposure to diesel exhaust or its byproducts, regardless of whether you live in a rural or urban setting. However, people living and working in urban and industrial areas are more likely to be exposed to this pollutant. Those spending time on or near roads and freeways, truck loading and unloading operations, operating diesel-powered machinery or working near diesel equipment face exposures to higher levels of diesel exhaust and face higher health risks.
The following tables illustrate the exposure to diesel particulate matter (DPM) in occupational and non-occupational settings.
Table 1: Ranges of occupational exposure to DPM by job category
| Year of Sampling |
Occupations |
Occupational DPM, ug/m |
| 1980’s and 1990’s |
Miners |
10-1,280 |
| 1980's |
Railroad Workers |
39-191 |
| 2985 and later |
Firefighters |
4-748 |
| NA |
Airport crew, public transit workers |
7-98 |
| 1990 |
Dockworkers, mechanics |
5-61 |
| 1990 |
Long-and short-haul truckers |
2-7 |
Table 2: Annual average nationwide DPM exposure estimates (ug/m_)
|
Demographic group
|
1990 |
1996 |
| 50-State population |
0.8 |
0.7 |
| Rural population |
0.5 |
0.3 |
| Urban population |
0.9 |
0.7 |
| Urban outdoor workers |
1.1 |
0.8 |
| Urban children (0-17) |
0.9 |
0.7 |
Source: http://www.epa.gov/ncea/dieslexh.htm
Exposure to diesel exhaust can have immediate health effects. Diesel exhaust can irritate the eyes, nose, throat and lungs, and it can cause coughs, headaches, light-headedness and nausea. In studies with human volunteers, diesel exhaust particles made people with allergies more susceptible to the materials to which they are allergic, such as dust and pollen. Exposure to diesel exhaust also causes inflammation in the lungs, which may aggravate chronic respiratory symptoms and increase the frequency or intensity of asthma attacks.
Diesel exhaust is a major source of fine-particle pollution. The elderly and people with emphysema, asthma, and chronic heart and lung disease are especially sensitive to fine-particle pollution. Because children’s lungs and respiratory systems are still developing, they are also more susceptible than healthy adults to fine particles.
.Like all fuel-burning equipment, diesel exhaust contains nitrogen oxides. Nitrogen oxides can damage lung tissue, lower the body’s resistance to respiratory infection and worsen chronic lung diseases, such as asthma. They also react with other pollutants in the atmosphere to form ozone, a major component of smog.
The tables below show the biological impact of the gas phase and particulate phase of diesel engine emissions.
Table 3: Major components of gas-phase diesel engine emissions, their known
atmospheric transformation products, and the biological impact of the reactants and products
| Gas-phase emission Component |
Atmospheric reaction products |
Biological impact
|
| Carbon dioxide |
-- |
Major contributor to global warming |
| Carbon monoxide |
-- |
Highly toxic to humans, blocks |
| Oxides of nitorgen |
Nitric acid, ozine |
Nitrogen dioxide is a respiratory tract irritant and major ozone precursor. Nitric acid contributes
to acid rain.
|
| Sulfur dioxide |
Sulfuric acid |
Respiratory tract irritation.
Contributor to acid rain.
|
| Hydrocarbons: |
|
|
Alkanes (C18)
|
Aldehydes, alkyl nitrates,
ketones
|
Respiratory tract irritation.
Reaction products are ozone
precursors (in the presence of NOx).
|
Alkenes (C4)
(e.g., 1,3-butadiene)
|
Aldehydes, ketones |
Respiratory tract irritation. Some alkenes are mutagenic and carcinogenic. Reaction products are ozone precursors (in the presence of NOx). |
| Aldehydes: |
|
|
| Formaldehyde |
Carbon monoxide,
hydroperoxyl radicals
|
Formaldehyde is a probable human carcinogen and an ozone precursor (in the presence of NOx). |
Higher aldehydes (e.g.,
acetaldehyde, acrolein
|
Peroxyacyl nitrates |
Respiratory tract and eye irritation;
causes plant damage
|
Monocyclic aromatic
compounds (e.g., benzene,
toluene)
|
Hydroxylated and
hydroxylated-nitro derivativesa
|
Benzene is toxic and carcinogenic in humans. |
Benzene is toxic and carcinogenic in humans.
|
Nitro-PAHs (4 rings) |
Some of these PAHs and nitro-PAHs are known mutagens and carcinogens.
|
Source: Health Effects Institute, 1995.
Table 4: Major components of particle-phase diesel engine emissions, their known atmospheric transformation products, and the biological impact of the reactants and products.
Particle-phase
emission component |
Atmospheric reaction
products |
Biological impact |
| Elemental carbon |
|
Nuclei adsorb organic compounds |
Inorganic sulfate and
Nitrate
|
|
Respiratory tract irritation |
| Hydrocarbons (C14-C35) |
Little information; possibly aldehydes, ketones, and alkyl nitrates
|
Unknown |
PAHs (4 rings) (e.g.,
pyrene, benzo[a]pyrene)
|
Nitro-PAHs (4 rings) Nitro-PAH lactones
|
Larger PAHs are major contributors of carcinogens in combustion emissions. Many nitro-PAHs are potent mutagens and carcinogens. |
Source: Health Effects Institute, 1995.
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