11th Roc: Diesel Exhaust Particulates
SUBSTANCE PROFILES
RUNNING
expected load, fuel composition, and engine emission controls.
Diesel Exhaust Particulates*
Typically light-duty vehicles such as automobiles and light trucks
Reasonably anticipated to be a human carcinogen
operate at higher speeds than heavy-duty vehicles such as trucks. The
First Listed in the Ninth Report on Carcinogens (2000)
total particulate emission concentration from light-duty diesel engines is
much smaller than from heavy-duty diesel engines. In general, newer
Carcinogenicity
heavy-duty trucks emit diesel particulates at a rate 20 times greater than
Exposure to diesel exhaust particulates is reasonably anticipated to be a
catalyst-equipped gasoline-fueled vehicles (WHO 1996). However,
human carcinogen, based on limited evidence of carcinogenicity from
depending on operating conditions, fuel composition, and engine
studies in humans, which indicates elevated lung cancer rates in
control technology, light-duty diesel engines and heavy-duty diesel
occupational groups exposed to diesel exhaust (IARC 1989, Cohen
engines can emit 50 to 80 times and 100 to 200 times, respectively,
and Higgens 1995, Bhatia et al. 1998) and supporting animal and
more particulate mass than typical catalytically equipped gasoline
mechanistic studies. An increased risk of lung cancer is found in the
engines (McClellan 1986).
majority of human studies. The overall relative risk is approximately
The particle size distribution of diesel exhaust is bi-modal with a
1.3, and higher risks are found in more heavily exposed subgroups in
nuclei mode (0.0075 to 0.042 µm in diameter) and an accumulation
some studies. The increased risk is not readily explained by
mode (0.042 to 1.0 µm in diameter) (Baumgard and Johnson 1996),
confounding by either smoking or asbestos exposure. However, the
most of which occur in aerodynamic diameters ranging from 0.1 to
increased risk cannot always be clearly ascribed to diesel exhaust
0.25 µm in diameter (Groblicki and Begeman 1979, Dolan et al. 1980,
exposure. Although some studies employed semiquantitative estimates
NRC 1982, Williams 1982). Approximately 98% of the particles
of diesel exhaust exposure (Steenland et al. 1998), most studies used
emitted from diesel engines are less than 10 microns in diameter, 94%
inadequate measures of exposure.
less than 2.5 microns in diameter, and 92% less than 1.0 microns in
Studies of the carcinogenicity of diesel exhaust particulates in
diameter (ARB 1997).
animals have shown a consistent lung tumor response in rats but not
Engines running under low load typically produce fewer particles
in the mouse or hamster. The response in rats appears to be due to the
with a higher proportion of organic compounds associated with the
particulate component of exhaust, as the filtered vapor phase of
available particle mass. Conversely, engines under high load typically
exhaust has been shown not to be tumorigenic. Solvent extracts of
produce more particulate matter with a lower proportion of organic
diesel exhaust particles are carcinogenic when applied to the skin or
compounds associated with available particles. Kishi et al. (1992) found
administered by intratracheal instillation or intrapulmonary
that exhaust gas temperatures affect particle composition. Low exhaust
implantation to rats, mice, or hamsters.
gas temperatures produce particulate matter with more adsorbed soluble
organics than particulate matter produced in a high exhaust gas
Additional Information Relevant to Carcinogenicity
temperature environment.
Diesel exhaust is a complex mixture of combustion products of diesel
The emissions consist of a nonpolar fraction (57%), a moderately
fuel, with the exact composition depending on the type of engine, the
polar fraction (9%), and a polar fraction (32%) (Schuetzle 1983,
speed and load at which it is run, and the composition of the fuel
Schuetzle et al. 1985), with the remainder unrecoverable. Diesel engines
used. Diesel exhaust contains identified mutagens and carcinogens
operate with excess air (~25-30 parts air to 1 part fuel) (Lassiter and
both in the vapor phase and associated with respirable particles. Diesel
Milby 1978). The gas phase fraction is composed primarily of typical
exhaust particles are considered likely to account for the human lung
combustion gases such as nitrogen, oxygen, carbon dioxide, and water
cancer findings because they are almost all of a size small enough to
vapor. As a result of incomplete combustion, the gaseous fraction also
penetrate to the alveolar region. Mutagenic and carcinogenic
contains pollutants such as carbon monoxide, sulfur oxides, nitrogen
chemicals, including polyaromatic hydrocarbons and nitroarenes, have
oxides, volatile hydrocarbons, and low molecular weight polyaromatic
been extracted from these particles with organic solvents, or with a
hydrocarbons (PAHs) and their derivatives.
lipid component of mammalian lung surfactant.
The inorganic fraction of the particulate phase of diesel fuel
While diesel particulate exposures produce lung cancer in rats, the
combustion emissions primarily consists of small elemental carbon
relevance of this result in predicting the human response has been
particles ranging from 0.01 to 0.08 µm in diameter. The organic and
questioned. Diesel exhaust particulate exposure produces a spectrum of
elemental carbon accounts for approximately 80% of the total
inflammatory and neoplastic pulmonary responses in the rat that are
particulate matter mass. The remaining 20% is composed of sulfate
characteristic of responses also seen with other inhaled particles of varying
(mainly sulfuric acid) (Pierson and Brachaczek 1983) and some
toxicity. These responses are apparently little influenced by the chemical
inorganic additives and components of fuel and motor oil.
constituents of the particles. Although the precise bioavailability of
In general, the organic compounds identified in diesel exhaust
chemical mutagens and carcinogens from inhaled diesel particulates is
emissions contain hydrocarbons, hydrocarbon derivatives, PAHs, PAH
not known, DNA adducts have been found in the lung of rats exposed to
derivatives, multifunctional derivatives of PAHs, heterocyclic
diesel exhaust particulates. Similarly, more lymphocyte-DNA adducts
compounds, heterocyclic derivatives, and multifunctional derivatives of
were found in groups occupationally exposed to diesel exhaust than in
heterocyclic compounds (Schuetzle 1988). The organic fractions consist
groups with lower or ambient exposures. However, diesel exhaust
of soluble organic compounds such as aldehydes, alkanes, alkenes, and
exposure was not quantified in these studies, and exposure to used motor
high molecular weight PAHs and PAH-derivatives.
oil may have contributed to the adducts observed in one study.
Because of their high surface area, diesel exhaust particulates are
capable of adsorbing relatively large amounts of organic material. The
Properties
adsorbed elements come from unburned fuel, lubricating oil, and
Diesel exhaust is a complex mixture of combustion products of diesel
pyrosynthesis during fuel combustion. A variety of mutagens and
fuel, with the exact composition dependent upon the type of engine,
carcinogens such as PAH and nitro-PAH (NRC 1982, Tokiwa and
operating conditions, lubricating oil, additives, emission control system,
Ohnishi 1986, WHO 1996) are adsorbed by the particulates. There is
and the composition of the fuel used (Ullman 1989, Obert 1973).
sufficient evidence for the carcinogenicity for 15 PAHs (a number of
Diesel engines are typically separated according to their service
these PAHs are found in diesel exhaust particulate emissions) in
requirements, light-duty or heavy-duty. The operating conditions for
experimental animals. The nitroarenes (five listed) meet the
light-duty and heavy-duty diesel engines differ in terms of engine speed,
established criteria for listing as reasonably anticipated to be a human
REPORT ON CARCINOGENS, ELEVENTH EDITION
RUNNING
SUBSTANCE PROFILES
carcinogen based on carcinogenicity experiments with laboratory
temperatures. This study showed no discernible difference between
animals. The organic extractable fraction of diesel exhaust particulates
the exposure levels of truckers (3.8 µg/m3) and highway background
is typically in the 20% to 30% range but it may be as high as 90%
concentrations (2.5 µg/m3). These results indicate that the highway
(Williams et al. 1989), depending upon vehicle type and operating
environment, rather than the truck itself, is the cause of the truck
conditions. In general, incomplete combustion in diesel engines
driver’s exposure (Zaebst et al. 1991).
operating under low load conditions produces relatively low particle
Firefighters in New York, Boston, and Los Angeles were studied to
concentrations and a higher proportion of organic-associated particles
determine exposure to diesel exhaust particulates (Froines et al. 1987).
(Dutcher et al. 1984).
Total exposure to airborne particles was measured using personal air
samplers. Approximately 86% of the study population were
Use
nonsmokers. Smokers were exposed to higher average airborne particle
No known uses of diesel exhaust particulates exist.
concentrations than were nonsmokers. Sampling was performed only
when firefighters were in the fire stations. For the three cities, total
Production
airborne particulate exposure had a time-weighted average (TWA)
Internal combustion engines have been used in cars, trucks,
ranging from below 100 µg/m3 to 480 µg/m3. An average particulate
locomotives, and other motorized machinery for approximately 100
exposure of 300 µg/m3 was measured in Boston and New York. After
years (IARC 1989). The combustion of diesel fuel in a compression
adjustment for background levels and smoking (75 µg/m3), firefighters
ignition engine produces diesel exhaust. Engine exhaust contains
in these two cities were exposed to a total diesel exhaust particulates
thousands of gaseous and particulate substances. There are three major
level of 225 µg/m3. Los Angeles had the highest exposure levels of the
groups of diesel exhaust sources: mobile sources (on-road vehicles and
three cities. For a “worst-case” scenario, the mean concentration levels
other mobile sources), stationary area sources (oil and gas production
were as high as 748 µg/m3. The authors noted that these were busy
facilities, stationary engines, repair yards, shipyards etc.), and stationary
fire stations located in large metropolitan areas. Other factors such as
point sources (chemical manufacturing, electric utilities, etc.). The
smoking, building design, age and maintenance of vehicles, activities
composition and quantity of the emissions from an engine depend
of the firefighters, and timing of runs also affected results.
mainly on the type and condition of the engine, fuel composition and
Three studies reviewed by the IARC (1989) found that toll-booth
additives, operating conditions, and emission control devices.
workers had elevated levels of exposure to carbon monoxide (although this
was decreased with ventilation systems) and diesel exhaust particulates.
Exposure
carbon monoxide exposure also was elevated among border-station and
Various employee groups have been studied to determine their
motor vehicle inspectors and parking garage attendants (IARC 1989). In
occupational exposures to diesel exhaust particulates. They include
many of these studies, however, it was difficult to differentiate between
railroad workers, mine workers (who use diesel-powered equipment),
gasoline exhaust and diesel exhaust. Numerous studies have combined the
bus garage workers, trucking company workers, fork-lift truck
two types of exhausts together. Therefore, exact determinations of diesel
operators, firefighters, lumberjacks, toll-booth and parking garage
exhaust particulates exposure is difficult in these cases.
attendants, and many professions servicing or handling automobiles
Regulations
(car mechanics, professional drivers, etc.). The National Institute for
EPA
Occupational Safety and Health (NIOSH) has estimated that
Clean Air Act
approximately 1.35 million workers are occupationally exposed to
Control of Emissions of Hazardous Air Pollutants from Mobile Sources: Listed as a
diesel exhaust particulates in approximately 80,000 workplaces in the
Mobile Source Air Toxic for which regulations are to be developed
United States (MMWR 1989).
Guidelines
Railroad workers’ potential for exposure has increased since 1959,
NIOSH
when almost all the U.S. railroad system (95%) was converted to diesel
Diesel exhaust listed as a potential occupational carcinogen
engines. Varying degrees of exposure to diesel exhaust particulates
(from 17 µg/m3 for clerks to 134 µg/m3 for locomotive shop workers)
*No separate CAS registry number assigned to diesel exhaust particulates.
has been reported based upon job groups (Woskie et al. 1988).
Diesel engines have been, and continue to be, commonly used in
REFERENCES
U.S. mines since their first introduction in the early 1950s. Exposure
Apol, A. G. 1983. Health Hazard Evaulation, Regional Transportation District, Denver CO. HETA-82-137-
occurs from activities that use diesel-fueled heavy machinery, such as
1264. Cincinnati, OH: National Institute for Occupational Safety and Health.
ARB. 1997. Emission Inventory, 1995. Air Resource Board, Technical Support Division.
blasting. Holland (1978) conducted an exposure study in 24 U.S. coal
Baumgard, K. J. and J. H. Johnson. 1996. The Effect of Fuel and Engine Design on Diesel Exhaust Particle
mines and showed that, while certain PAHs expected from diesel
Size Distributions. SAE Technical Paper Series, #960131.
exhaust particulates were found (anthracene and phenanthrene), other
Bhatia, R., P. Lopipero and A. H. Smith. 1998. Diesel exhaust exposure and lung cancer. Epidemiology 9(1): 84-91.
Cohen, A. J. and M. W. P. Higgins. 1995. Diesel Exhaust. A Critical Analysis of Emissions, Exposure, and
PAHs (benz[a]anthracene, benz[a]pyrene, benz[e]pyrene, chrysene,
Health Effects. Health Effects Institute.
and pyrene) were not found in measurable quantities. Cornwell
Cornwell, R. J. 1982. Health Hazard Evaluation Determination: Climax Molybdenum Company, Climax, CO.
(1982) found other PAHs not found in Holland’s study in diesel
Report No. MHETA-81-108-9004, PB84-14850 1. Morgantown, WV.
Dolan, D. F., D. B. Kittelson and D. Y. H. Pui. 1980. Diesel Exhaust Particle Size Distribution Measurement
emissions from a molybdenum mine in Colorado. This mine was
Techniques. SAE Technical paper # 870254.
equipped with drills and various load haul-dumps.
Dutcher, J. S., J. D. Sun, J. A. Lopez, I. Wolf, R. K. Wolff and R. O. McClellan. 1984. Generation and char-
Bus repair facilities were studied to determine diesel exhaust
acterization of radiolabeled diesel exhaust. Am Ind Hyg Assoc J 45(7): 491-8.
Froines, J. R., W. C. Hinds, R. M. Duffy, E. J. Lafuente and W. C. Liu. 1987. Exposure of firefighters to
emissions (Apol 1983). The highest exposure levels were observed
diesel emissions in fire stations. Am Ind Hyg Assoc J 48(3): 202-7.
when buses were started at peak times of dispatch and return. Pryor
Groblicki, P. J. and C. R. Begeman. 1979. Particle size variation in diesel car exhaust. SAE Technical paper
(1983) studied area levels of diesel exhaust particulates at a bus garage.
#790421. Society of Automotive Engineers.
Holland, W. D. 1978. Determination of Breathing Zone Concentration of Contaminants from Emission from
Elevated levels of diesel exhaust emissions were observed during peak
Diesel Powered Vehicles in Underground Mines. BuMines OFR 24-80; U.S. NTIS Pb80-150776.
hours of bus activity. Levels rapidly returned to normal 10 to 15
Washington, D.C.: U.S. Department of the Interior, Bureau of Mines.
minutes after the passing of peak times. Using elemental carbon,
IARC. 1989. Diesel and Gasoline Engine Exhausts and Some Nitroarenes. IARC Monographs on the
Zaebst et al. (1991) found an effective way of determining truck
Evaluation of Carcinogenic Risk of Chemicals to Humans, vol. 46. Lyon, France: International Agency
for Research on Cancer. 458 pp.
drivers’ exposure to diesel exhaust particulates. Temperature was an
Kishi, Y., H. Tohno and M. Ara. 1992. Characteristics and Combustability of Particulate Matter. Reducing
important factor with higher exposures occurring at higher
Emissions from Diesel Combustion. Warrendale, PA: Society of Automotive Engineers. p. 139-146.
REPORT ON CARCINOGENS, ELEVENTH EDITION
SUBSTANCE PROFILES
RUNNING
Lassiter, D. V. and T. H. Milby. 1978. Health Effects of Diesel Exhaust Emission: A Comprehensive
Literature Review, Evaluation and Research Gaps Analysis. U.S. NTIS PB-282-795. Washington, D.C.:
American Mining Congress.
McClellan, R. O. 1986. 1985 Stokinger lecture. Health effects of diesel exhaust: a case study in risk
assessment. Am Ind Hyg Assoc J 47(1): 1-13.
MMWR. 1989. Publication of NIOSH Current Intelligence Bulletin on Carcinogenic Effects of Diesel
Exhaust. Morbid Mort Weekly Report 38: 76-78.
NCR. 1982. Diesel cars: benefits, risks, and public policy, final report of the Diesel Impacts Study
Committee. Washington, D.C.: National Academy Press.
Obert, E. F. 1973. Internal Combustion Engines and Air Pollution. Harper and Row.
Pierson, W. R. and W. W. Brachaczek. 1983. Particulate matter associated with vehicles on the road II.
Aerosol. Sci Tech 2: 1-40.
Pryor, P. 1983. Trailways Bus System, Denver CO. Health Hazard Evaluation Report No. HETA 81-416-1334.
Cincinnati, OH: National Institute of Occupational Safety and Health.
Schuetzle, D. 1983. Sampling of vehicle emissions for Chemical Analysis and biological testing. Environ
Health Perspect 47: 65-80.
Schuetzle, D. 1988. Organic tracers for source apportionment of combustion emissions to ambient air par-
ticulates. In Proceedings of the Sixth Symposium on Environmental Analytical Chemisty and Source
Apportionment in Ambient and Indoor Atmospheres.
Schuetzle, D., T. E. Jensen and J. C. Ball. 1985. Polar PAH derivatives in extracts of particulates: Biological
characterization and techniques for chemical analysis. Environ Int 11: 169-181.
Steenland, K., J. Deddens and L. Stayner. 1998. Diesel exhaust and lung cancer in the trucking industry:
exposure-response analyses and risk assessment. Am J Ind Med 34(3): 220-8.
Tokiwa, H. and Y. Ohnishi. 1986. Mutagenicity and carcinogenicity of nitroarenes and their sources in the
environment. Crit Rev Toxicol 17(1): 23-60.
Ullman, T. L. 1989. Investigation of the Effects of Fuel Composition on Heavy Duty Diesel Engine
Emissions. SAE Technical Paper No. 892072. Society of Automotive Engineers.
WHO. 1996. Diesel Fuel and Exhaust Emissions. Geneva: World Health Organization.
Williams, D. J., J. W. Milne and D. B. K. Roberts, M.C. 1989. Particulate emission from "in use" motor
vehicles - II Diesel vehicles. Atmos Environ 23: 2647-2661.
Williams, R. L. 1982. Diesel particulate emissions: composition, concentration, and control. Dev Toxicol
Environ Sci 10: 15-32.
Woskie, S. R., T. J. Smith, S. K. Hammond, M. B. Schenker, E. Garshick and F. E. Speizer. 1988. Estimation
of the diesel exhaust exposures of railroad workers: I. Current exposures. Am J Ind Med 13(3): 381-94.
Zaebst, D. D., D. E. Clapp, L. M. Blade, D. A. Marlow, K. Steenland, R. W. Hornung, D. Scheutzle and J.
Butler. 1991. Quantitative determination of trucking industry workers’ exposures to diesel exhaust
particles. Am Ind Hyg Assoc J 52(12): 529-41.
REPORT ON CARCINOGENS, ELEVENTH EDITION
