Xylenes (Mixed Isomers)
o-XYLENE
m-XYLENE
p-XYLENE
1330-20-7, 95-47-6, 108-38-3, 106-42-3
Hazard Summary
Commercial or mixed xylene usually contains about 40-65% m-xylene and up to 20% each of o-xylene
and p-xylene and ethylbenzene. Xylenes are released into the atmosphere as fugitive emissions from
industrial sources, from auto exhaust, and through volatilization from their use as solvents. Acute (short-
term) inhalation exposure to mixed xylenes in humans results in irritation of the eyes, nose, and throat,
gastrointestinal effects, eye irritation, and neurological effects. Chronic (long-term) inhalation exposure of
humans to mixed xylenes results primarily in central nervous system (CNS) effects, such as headache,
dizziness, fatigue, tremors, and incoordination; respiratory, cardiovascular, and kidney effects have also
been reported. EPA has classified mixed xylenes as a Croup D, not classifiable as to human
carcinogenicity.
Please Note: The main sources of information for this fact sheet are EPA's Integrated Risk Information System (IRIS)
(6), which contains information on oral chronic toxicity and the RfD, and the Agency for Toxic Substances and
Disease Registry's (ATSDR's) Toxicological Profile for Xylenes. (1)
Uses
s Mixed xylenes are used in the production of ethylbenzene, as solvents in products such as paints and
coatings, and are blended into gasoline. (1)
Sources and Potential Exposure
s Mixed xylenes are distributed throughout the environment; they have been detected in air, rainwater, soils,
surface water, sediments, drinking water, and aquatic organisms. (1)
a Xylenes are released into the atmosphere as fugitive emissions from industrial sources, from auto exhaust,
and through volatilization from their use as solvents. (1)
a Ambient air concentrations of mixe d xylenes in urban areas of the United States range from 0.003 to 0.38
milligrams per cubic meter (mg/m 1(1)
a Mixed xylenes have also been detected at low levels in indoor air; xylenes have been widely used in home
use products such as synthetic fragrances ^nd paints. One study reported concentrations of m- and p-
xylene ranging from 0.01 0 to 0.047 mg/m . (1)
a Levels of mixed xylenes in drinking water have been reported to range from 0.2 to 9.9 micrograms per liter
(|jg/L), with mean concentrations of less than 2 |jg/L. (1)
a Occupational exposure to mixed xylenes may occur at workplaces where mixed xylenes are produced and
used as industrial solvents. (1)
a Xylene exposure may be to any of the three isomers or to mixtures of the isomers. (1)
Assessing Personal Exposure

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Exposure to mixed xylenes may be determined by measuring the breakdown products of mixed xylenes in
the urine or by measuring levels of xylene in blood or exhaled breath. (1)
Health Hazard Information
Acute Effects:
a Human and animal data show that all xylene isomers or xylene mixtures produce similar effects, although
specific isomers may not be equally potent in producing the effects. (1)
s Acute inhalation exposure to mixed xylenes in humans has been associated with dyspnea and irritation of
the nose and throat; gastrointestinal effects such as nausea, vomiting, and gastric discomfort; mild
transient eye irritation; and neurological effects such as impaired short-term memory, impaired reaction
time, performance decrements in numerical ability, and alterations in equilibrium and body balance. (1-3)
a Acute dermal exposure in humans results in transient skin irritation and dryness and scaling of the skin.
(1-3)
a Acute inhalation exposure to a mixture of toluene and xylenes resulted in more than additive respiratory
and neurological toxicity in humans and animals. (1)
a Acute animal studies have reported respiratory, cardiovascular, CNS, liver, and kidney effects from
inhalation exposure to mixed xylenes. (1)
a Acute animal tests in rats and mice have shown mixed xylenes to have low to moderate toxicity from
inhalation exposure and moderate toxicity from oral exposure. (4,5)
Chronic Effects (Noncancer):
a Chronic exposure of humans to mixed xylenes, as seen in occupational settings, has resulted primarily in
neurological effects such as headache, dizziness, fatigue, tremors, incoordination, anxiety, impaired short-
term memory, and inability to concentrate. Labored breathing, impaired pulmonary function, increased
heart palpitation, severe chest pain, abnormal EKG, and possible effects on the kidneys have also been
reported. (1,2)
a Mixed xylenes have not been extensively tested for chronic effects, although animal studies show effects on
the liver and CNS from inhalation and oral exposures and effects on the kidneys from oral exposure to
mixed xylenes. (1)
a The Reference Dose (RfD) for mixed xylenes is 2 milligrams per kilogram body weight per day (mg/kg/d)
based on hyperactivity, decreased body weight, and increased mortality in rats, and the
provisional RfD for m- and o-xylenes is also 2 mg/kg/d. EPA has not established an RfD for p-xylene.
The RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral 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 RfD, the potential for
adverse health effects increases. Lifetime exposure above the RfD does not imply that an adverse health
effect would necessarily occur. The provisional RfDs are values that have had some form of Agency review,
but do not appear on IRIS. (6,1 0)
a EPA has medium confidence in the study on which the RfD was based because it was a well-designed study
in which adequately sized groups of two species we re tested over a substantial portion of their lifespan,
comprehensive histology was performed, and a no-observed-adverse-effect level (NOAEL) was defined; but
clinical chemistries, blood enzymes, and urinalysis were not performed; medium confidence in the
database because although supporting data exist for mice, and teratogenicity and fetotoxicity data are
available with positive results at high oral doses, a lowest-observed-adverse-effect level (LOAEL) for
chronic oral exposure has not been defined; and, consequently, medium confidence in the RfD. (6)
a EPA has not established a Reference Concentration (RfC) for mixed xylenes or an^y isomers. (6)
a ATSDR has calculated a chronic inhalation minimal risk level (MRL) of 0.4 mg/m (0.1 parts per million
[ppm]) for mixed xylenes based on neurological effects in occupationally exposed workers. The MRL is an

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estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk
of adverse noncancer health effects over a specified duration of exposure. (1)
Reproductive/Develop mental Effects:
s Several human studies examined exposure to organic solvents (including mixed xylenes) and
developmental effects. An increased potential for spontaneous abortions among the wives of
occupationally exposed men was reported. However, no conclusions can be drawn from these studies
because they all involved concurrent exposure to multiple chemicals. (1)
s Mixed xylenes have been shown to produce developmental effects, such as an increased incidence of
skeletal variations in fetuses, delayed ossification, fetal resorptions, and decreased fetal body weight in
animals via inhalation exposure. Some studies observed maternal toxicity as well. (1 -3)
Cancer Risk:
a No information is available on the carcinogenic effects of mixed xylenes in humans. (1)
a An increase in tumors was not reported in rats or mice exposed to mixed xylenes via gavage
(experimentally placing the chemical in the stomach). Other animal studies have reported equivocal
results. (1,3,6)
a EPA has classified mixed xylenes as a Group D, not classifiable as to human carcinogenicity. (6)
Physical Properties
a m-, o-, and p-Xylene are the three isomers of xylene: commercial or mixed xylene usually contains about
40-65% m-xylene and up to 20% each of o- and p-xylene and ethylbenzene. (1)
a Mixed xylenes are colorless liquids that are practically insoluble in water and have a sweet odor. (1)
a The odor threshold for m-xylene is 1.1 ppm. (4)
a The chemical formula for mixed xylenes is C H , and the molecular weight is 1 06.1 6 g/mol. (1)
8 10
" The vapor pressure for mixed xylenes is 6.72 m m Hg at 21 °C, and the log octanol/water partition
coefficient (log K ) is 3.1 23.20. (1)
ow
Conversion Factors:
To convert concentrations in air (at 25 "O from ppm ttrng/m': mg/n,3 - (ppm) X (molecular weight of the 3
compo^und)/(24.45). For xylenes: 1 ppm = 4.34 mg/m . To convert concentrations in air from |jg/m to mg/m :
mg/m = (pg/m ) x (1 mg/1,000 |jg).
Health Data from Inhalation Exposure

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Xylenes
100000
10000
n 1000
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B
E
e
d
1
*
fl
100
10
0.1
Regulatory, advisory
numbers'*
Health numbers
NIOSH IDLH (3,SOO nrg/nfr
ACGIH ST EL- NIOSH STEL
(655 rng/mfl
ACGIH TLV, NDSH
LOAELc (human)
_ (61 mg/n?)
ATSDR chronic
MRL
(0.4 rng/rrb
EeL
HsL
LC^tmixad xylane s) (27,571 mg/rifl)
LCb (p-jqrla ns) (16,96 3 mg/rft
ACGIH STEL—American Conference of Governmental and Industrial Hygienists' short-term exposure limit; 1 5-min
time-weighted-average exposure that should not be exceeded at any time during a workday even if the 8-h time-
weighted-average is within the threshold limit value.
ACGIH TLV—ACGIH's threshold limit value expressed as a time-weighted average; the concentration of a substance
to which most workers can be exposed without adverse effects.
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.
NIOSH REL—NIOSH's recommended exposure limit; NIOSH-recommended exposure limit for an 8- or 1 0-h time-
weighted-average exposure and/or ceiling.
NIOSH STEL—NIOSH's recommended short-term exposure limit; a 1 5-minute TWA exposure which should not be
exceeded at any time during a workday.
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 and ACGIH numbers are advisory.
c
This LOAEL is from the critical study used as the basis for the ATSDR chronic inhalation MRL.
Summary created in April 1992, updated in January 2000
References
1.	Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Xylenes (Update).
Public Health Service, U.S. Department of Health and Human Services, Altanta, GA. 1 995.
2.	E.J. Calabrese and E.M. Kenyon. Air Toxics and Risk Assessment. Lewis Publishers, Chelsea, Ml. 1 991.
3.	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.
4.	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. 1 983.
5.	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.
6.	U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Xylenes. National
Center for Environmental Assessment, Office of Research and Development, Washington, DC. 1 999.
7.	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. 1 999.
8.	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. 1 997.
9.	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 0. U.S. Environmental Protection Agency. Health Effects Assessment Summary Tables. FY 1 997 Update. Office
of Research and Development, Office of Emergency and Remedial Response, Washington, DC. EPA/540/R-
97-036. 1997.
A. x This fact sheet refers to the mixture of all three isomers of mixed xylenes as "mixed mixed xylenes" and the
isomers by their individual isomer names.

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