Propylene oxide
75-56-9
Hazard Summary
Propylene oxide is used in the production of polyethers (the primary component of polyurethane foams)
and propylene glycol. Acute (short-term) exposure of humans and animals to propylene oxide has caused
eye and respiratory tract irritation. Dermal contact, even with dilute solutions, has caused skin irritation
and necrosis in humans. Propylene oxide is also a mild central nervous system (CNS) depressant in
humans. Inflammatory lesions of the nasal cavity, trachea, and lungs and neurological effects have been
observed in animals chronically (long-term) exposed to propylene oxide by inhalation. Propylene oxide has
been observed to cause tumors at or near the site of administration in rodents, causing forestomach
tumors following ingestion via gavage (experimentally placing the chemical in the stomach) and nasal
tumors after inhalation exposure. EPA has classified propylene oxide as a Group B2, probable human
carcinogen.
Please Note: The main sources of information for this fact sheet are EPA's Integrated Risk Information System (IRIS)
(5), which contains information on inhalation chronic toxicity of propylene oxide and the RfC and the carcinogenic
effects of propylene oxide including the unit cancer risk for inhalation exposure, and EPA's Summary Review of the
Health Effects Associated with Propylene Oxide. (2)
Uses
s The major use of propylene oxide is in the production of polyethers (the primary component of
polyurethane foams) and propylene glycol. (2)
s Propylene oxide is also used in the fumigation of foodstuffs and plastic medical instruments and in the
manufacture of dipropylene glycol and glycol ethers, as herbicides, as solvents, and in the preparation of
lubricants, surfactants, and oil demulsifiers. (2,8)
Sources and Potential Exposure
a Occupational exposure by the inhalation and dermal routes related to the production, storage, transport,
and use of propylene oxide may be significant. However, occupational exposures are generally believed to
be less than 1 part per million (ppm). (1,2)
a Release of propylene oxide into the atmosphere is expected to primarily occur during its production or use
as an intermediate or as a fumigant and a soil sterilant. Inhalation of contaminated air in these areas may
provide a significant route of exposure. However, average atmospheric cone e^ nitrations at a distance of
more than 20 km from production facilities are estimated to be less than 1 0 ppm. (1,2)
a Propylene oxide has been detected in fumigated food products; consumption of contaminated food is
another possible route of exposure. (1,2)
Assessing Personal Exposure
¦ No information was located regarding the measurement of personal exposure to propylene oxide.
Health Hazard Information

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Acute Effects:
s Acute exposure of humans and animals to propylene oxide has caused eye and respiratory tract irritation.
As a respiratory irritant, coughing, dyspnea (difficulty in breathing), and pulmonary edema may result from
inhalation exposure and possibly lead to pneumonia. Dermal contact, even with dilute solutions, has
caused skin irritation and necrosis. (1-3)
s Propylene oxide is a mild CNS depressant. Acute exposure to high concentrations may cause headache,
motor weakness, incoordination, ataxia, and coma in humans. (1,3)
s Tests involving acute exposure of rats, mice, guinea pigs, and rabbits have demonstrated propylene oxide
to have moderate acute toxicity from inhalation, high acute toxicity from dermal exposure,
and moderate to high acute toxicity from ingestion. (4)
Chronic Effects (Noncancer):
a Health effects from chronic exposure to propylene oxide in humans have not been reported in the
literature.
a A significant decrease in body weight gain, increased mortality, and an increased incidence of inflammatory
lesions of the nasal cavity, trachea, and lungs have been observed in rodents chronically exposed to
propylene oxide by inhalation. (5)
a Chronic inhalation exposure to propylene oxide may cause some neuropathological changes in rats and
monkeys. (2,5)
3
• The Reference Concentration (RfC) for propylene oxide is 0.03 milligrams per cubic meter (mg/m ) based
on respiratory effects in rats. The RfC is an estimate (with uncertainty spanning perhaps an order of
magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups)
that is likely to be without appreciable risk of deleterious noncancer effects during a lifetime. It is not a
direct estimator of risk but rather a reference point to gauge the potential effects. At exposures
increasingly greater than the RfC, the potential for adverse health effects increases. Lifetime exposure
above the RfC does not imply that an adverse health effect would necessarily occur. (5)
a EPA has medium confidence in the study on which the RfC was based because the study used a large
number of animals, examined the critical effect with sensitive techniques and at multiple durations and
exposure levels, and was of chronic duration, but did not identify a no-observed-adverse-effect level
(NOAEL); medium confidence in the database because there were several corroborative chronic inhalation
studies and inhalation developmental studies, although the inhalation two-generation reproductive study
was inadequate; and, consequently, medium confidence in the RfC.
a EPA has not established a Reference Dose (RfD) for propylene oxide. (5)
Reproductive/Developmental Effects:
a No information is available on the reproductive or developmental effects of propylene oxide in humans,
a A study with rats and rabbits exposed to propylene oxide by inhalation prior to and during gestation
concluded that propylene oxide was harmful to the developing fetus but did not cause birth defects. In
rats, some degree of fetotoxicity was observed in all exposed groups (including a significant reduction in
the number of corpora lutea, implants, and live fetuses) and minor skeletal malformations in some; there
was no maternal mortality. Increased resorptions per litter were observed in rabbits. (2,5)
Cancer Risk:
a Human carcinogenicity data for propylene oxide are inadequate. (5)
a Propylene oxide has been observed to cause tumors at or near the site of administration in rodents,
causing forestomach tumors following exposure via gavage and nasal tumors after inhalation exposure.
(2,5,6)
a EPA has classified propylene oxide as a Group B2, probable human carcinogen. (5)
a EPA uses mathematical models, based on human and animal studies, to estimate the probability of a
person developing cancer from breathing air containing a specified concentration of a chemical. EPA
calculated an inhalation unit risk estimate of 3.7 x 1 0 (|jg/m ) . EPA estimates that, if an individual were

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to continuously breathe air containing propylene oxide at an average of 0.3 |jg/m (3x10 mg/m ) over
his or her entire lifetime, that person would theoretically have no more than a one-in-a-million increased
chance of developing cancer as a direct result of breathing air containing this chemical. Similarly, EPA
3	3
estimates that breathing air containing 3.0 |jg/m (0.003 mg/m ) would result in not greater than a one-
in-a-hmndred thousand increased chance of developing cancer, and air containing 30.0 |jg/m (0.03
mg/m ) would result in not greater than a one-in-ten thousand increased chance of developing cancer. For
a detailed discussion of confidence in the potency estimates, ^ please see IRIS. (5)
s EPA calculated an oral cancer slope factor of 0.24 (mg/kg/d) .(5)
Physical Properties
s The chemical formula of propylene oxide is C H O, and it has a molecular weight of 58.08 g/mol. (8)
3 6
* Propylene oxide occurs as a colorless, etherea I li quid that is extremely flammable. It is very soluble in
water. (2,8)
a The odor of propylene oxide is described as sweet, alcoholic, and ether-like with an odor threshold of 44
ppm. (3,9)
a Propylene oxide has a vapor pressure of 445 mm Hg at 20 °C and a log octanol/water partition coefficient
(log K ) of -0.1 3. (2)
ow
Conversion Factors:
3	3
To convert concentrations in air (at 2 5 °C) from ppm to mg/m ^ mg/m = (ppm) x (molecular weight of the
compo3und)/(24.45). For^propylene oxide: 1 ppm = 2.4 mg/m . To convert concentrations in air from |jg/m to
mg/m : mg/m = |jg/m x (1 mg/1,000 |jg).
Health Data from Inhalation Exposure

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Propylene Oxide
100000
10000
1000
OjOI
0.001
OjOOOI
Health numbers"
Regulatory, advisory
numbers'*
LCW ijnicaj (4,133 rng/nrft
LQAEL (mice) (71 mg/rrff
Rt (0.03 rng/nrf)
EPA Cancer Risk
Level (1-in-a
mill bn excess
lifetime risk) =
(3.0JCl04mg/rrfl
.
NIOSH IDLH (?5D mg/nrP)
AIHA ERPG-2 (395 mg/nrf)
OSHA PEL (240 rrg/rtfi
BsL pi
12 I Bel
AIHA ERPG-1 (119 mg/rm?)
ACGIH TLV
fre mg/rrf)

ACGIH TLV—American Conference of Governmental and Industrial Hygienists' threshold limit value expressed as a
time-weighted average; the concentration of a substance to which most workers can be exposed without adverse
effects.
AIHA ERPG—American Industrial Hygiene Association's emergency response planning guidelines. ERPG 1 is the
maximum airborne concentration below which it is believed nearly all individuals could be exposed up to one hour
without experiencing other than mild transient adverse health effects or perceiving a clearly defined objectionable
odor; ERPG 2 is the maximum airborne concentration below which it is believed nearly all individuals could be
exposed up to one hour without experiencing or developing irreversible or other serious health effects that could
impair their abilities to take protective action.
LC (Lethal Concentration )—A calculated concentration of a chemical in air to which exposure for a specific
50	50
length of time is expected to cause death in 50% of a defined experimental animal population.
LOAEL—Lowest-observed-adverse-effect level.
NIOSH IDLH — National Institute of Occupational Safety and Health's immediately dangerous to life or health
concentration; NIOSH recommended exposure limit to ensure that a worker can escape from an exposure condition
that is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from the
environment.
OSHA PEL—Occupational Safety and Health Administration's permissible exposure limit expressed as a time-
weighted average; the concentration of a substance to which most workers can be exposed without adverse effect
averaged over a normal 8-h workday or a 40-h workweek.
The health and regulatory values cited in this factsheet were obtained in December 1999.
a
Health numbers are toxicological numbers from animal testing or risk assessment values developed by EPA.
h

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Regulatory numbers are values that have been incorporated in Government regulations, while advisory numbers
are nonregulatory values provided by the Government or other groups as advice. OSHA numbers are regulatory,
whereas NIOSH, ACGIH, and AIHA numbers are advisory.
c
This LOAEL is from the critical study used as the basis for the EPA RfC.
References
Summary created in April 1 992, updated in January 2000
1.	U.S. Department of Health and Human Services. Hazardous Substances Data Bank (HSDB, online database).
National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1 993.
2.	U.S. Environmental Protection Agency. Summary Review of the Health Effects Associated with Propylene
Oxide. EPA/600/8-86/007F. Environmental Criteria and Assessment Office, Office of Health and
Environmental Assessment, Office of Research and Development, Research Triangle Park, NC. 1 987.
3.	G.D. Clayton and F.E. Clayton, Eds. Patty's Industrial Hygiene and Toxicology. Volume IIA, 3rd revised ed.
John Wiley & Sons, New York. 1 981.
4.	U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances (RTECS,
online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD.
1993.
5.	U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Propylene Oxide.
National Center for Environmental Assessment, Office of Research and Development, Washington, DC.
1999.
6.	International Agency for Research on Cancer (IARC). IARC Monographs on the Evaluation of the
Carcinogenic Risk of Chemicals to Humans: Allyl Compounds, Aldehydes, Epoxides and Peroxides. Volume
36. World Health Organization, Lyon. 1985.
7.	National Institute for Occupational Safety and Health (NIOSH). Pocket Guide to Chemical Hazards. U.S.
Department of Health and Human Services, Public Health Service, Centers for Disease Control and
Prevention. Cincinnati, OH. 1997.
8.	The Merck Index. An Encyclopedia of Chemicals, Drugs, and Biologicals. 1 1th ed. Ed. S. Budavari. Merck
and Co. Inc., Rahway, NJ. 1989.
9.	J.E. Amoore and E. Hautala. Odor as an aid to chemical safety: Odor thresholds compared with threshold
limit values and volatilities for 21 4 industrial chemicals in air and water dilution. Journal of Applied
Toxicology, 3(6):272-290. 1983.
1 0. Occupational Safety and Health Administration (OSHA). Occupational Safety and Health Standards, Toxic
and Hazardous Substances. Code of Federal Regulations 29 CFR 1 91 0.1 000. 1 998.
1 1. American Conference of Governmental Industrial Hygienists (ACGIH). 1 999 TLVs and BEIs. Threshold Limit
Values for Chemical Substances and Physical Agents. Biological Exposure Indices. Cincinnati, OH. 1999.
1 2. American Industrial Hygiene Association (AIHA). The AIHA 1 998 Emergency Response Planning Guidelines
and Workplace Environmental Exposure Level Guides Handbook. 1998.

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