United States
Environmental Protection
Office of Solid Waste
Emergency Response
OS-420 (WF)
January 1992
Leaking Underground
Storage Tanks
and Health
Health Risks
Petroleum Contamination

Printed on Recycled Paper

Understanding Health Risks From
Petroleum Contamination
U.S. Environmental Protection Agency
Office of Underground Storage Tanks
January 1992

Introduction 		1
Identifying Contaminants	3
Measuring Contaminants							7
Estimating Exposure 	 11
Assessing Health Effects 			 13
For Further Information , . . . .		 19
Figure 1. Free Product . 				.3
Figure 2. Fate and Transport of Selected Gasoline Constituents		 4
Figure 3. Vapor Fraction	5
Figure 4. Water Soluble Fraction 		5
Exhibit 1. Methods for Measuring Gasoline Constituents		 9
Exhibit 2. Health Effects Associated with Inhaling Gasoline Vapors	 14
Exhibit 3. Health Effects Associated with Ingesting Benzene in Water	15
Exhibit 4. Health Effects Associated with Inhaling Benzene Vapors	16

This document summarizes the potential
health effects associated with exposure to
gasoline (as a whole product), with particular
focus on its benzene constituent. A complete
understanding of the potential health effects
from exposure to gasoline requires the
consideration of other gasoline constituents as
well, such as ethylbenzene, toluene, and
Many State and local underground
storage tank (UST) programs rely heavily on
support from local and State health
departments for assistance in protecting
public health during the investigation and
cleanup of releases from USTs. Because
neither this nor any other single document
will enable field staff to function as industrial
hygienists or toxicologists, field staff are
encouraged to consult health experts on a
site-specific basis.
The purpose of this document is to
present clearly the health effects of benzene
exposure and what experts deem to be
adequate levels of protection. This document
is intended to help UST field staff: (1)
understand the potential hazards associated
with gasoline and benzene exposure and (2)
communicate them more effectively to the
public and health officials.
It is useful to remember that "risk" is
based on the statistical concept of probability
(i.e., that risk is a statement of likelihood, not
absolute certainty). The statistical evaluation
of risk depends on the existence of many
data samples. Because the data base for the
health effects of gasoline contamination is
small, this document generalizes from a
limited number of samples. Readers must
understand that this document is NOT
intended as a formal risk-assessment
instrument. It is NOT a "predictor" of
adverse health effects.
Whether or not adverse health effects
occur following exposure to a substance
depends upon the concentration and toxicity
of the substance; the type, extent, and
duration of the exposure; and the
susceptibility of the individual being exposed.
Understanding the potential for adverse
health effects from exposure to gasoline
requires the following four steps:
1.	Identifying and researching which
contaminants are involved;
2.	Determining how much of the chemical is
3.	Identifying who may be exposed to the
chemical and how to consider the type,
route, and duration of exposure; and,
4.	Assessing the potential health effects
associated with exposure.
Each of these steps is discussed in this

Intentionally Blank Page

The first step in understanding potential
health risks associated with the release of
gasoline from an underground storage tank
(UST) is determining the types of
contamination that exist. Gasoline is a
complex mixture of hydrocarbons composed
of over 200 different compounds, some of
which remain unidentified. The composition
of different batches of gasoline varies widely
as a result of chemical differences in naturally
occurring crude stocks and differences in
refining techniques.
Although each batch of gasoline differs,
many of the constituents of gasoline recur in
the batches time after time. The physical and
chemical properties of the constituents can be
used to predict how they will be transported
in the environment. Some of the constituents
are volatile; some are water soluble. Most
constituents are less dense than water and,
therefore, float on top of it. Following a
release from an UST, gasoline components
can be found: (1) as vapors, (2) solubilized in
water, (3) adsorbed to soil, or (4) floating on
water. The composition of a gasoline release,
therefore, depends not only on differences
among batches of refined gasoline but also on
where and when you look at the release.
Generally, the constituents of gasoline can
be divided into three categories: paraffins,
aroma tics, and olefins. Paraffins, which are
the largest class of compounds and often
comprise about 66 percent of the gasoline, are
composed of chains of carbons that are
singly-bonded to atoms of hydrogen (i.e.,
saturated hydrocarbons). Aroma tics are those
compounds whose structure includes a
benzene ring. Aroma tics often comprise
approximately 25 percent of gasoline and are
believed to be among its most toxic
constituents. (See Figure 1.) The commonly
recognized aromatic compounds—benzene,
toluene, ethylbenzene, and xylenes—are often
referred to as BTEX. Olefins are usually the
smallest group of constituents, consisting of
hydrocarbon chains that contain double or
triple bonds (i.e.,unsaturated hydrocarbons).
Figure 1. Free Product
The fate and transport of gasoline and its
constituents following a release from an UST
are summarized in Figure 2. After a release,
gasoline tends to flow downward through the
soil toward the groundwater table. Soil
characteristics and the depth to groundwater
determine how quickly gasoline and its
constituents reach groundwater. Porous soil
allows the gasoline to be transported quickly;
dense soil slows the transport. Once the
gasoline reaches the water table, it tends to
accumulate on top of it, because it is less
dense than water and is virtually insoluble in
it. If the soil has a high resistance to lateral
flow, accumulations of free product (i.e., that
petroleum product that would move through
the soil matrix under gravity) several feet
deep can occur.
The physical properties of the
constituents along with environmental
conditions affect the rate at which the free
product separates into different components.
Most of the paraffin constituents in gasoline
are volatile and readily vaporize into the air.


Primary Constituents Released into Sojl;
Paraffins:	Aromatics:
docane	1-methyl
methylcyclopentane -3-n-propylene
2.2.4-trimethytheptane	naphthalene
2.2.5-trimethylhexane	-	
Free Product Plume
Primary Constituents Released into Groundwater
Figure 2. Fate, and Transport of Selected Gasoline Constituents


. •««*.«
.*> .**

Figure 3. Vapor Fraction
Figure 4. Water Soluble Fraction
A smaller fraction of the olefins and
aromatics are volatile. Consequently, they
make up a smaller percentage of the vapors
in UST leaks than they do in free product.
Overall, gasoline vapors tend to be heavier
than air and are able to move laterally in
soils to enter basements of nearby structures.
See Figure 3.
The aromatic compounds are the most
water soluble constituents of gasoline. As a
result, the composition of the dissolved
ground-water contaminants is heavily
dominated by aromatics, such as BTEX.
Percolation of rain through the soil matrix or
fluctuations in the water table tend to
dissolve and carry these constituents,
increasing the rate at which they move
downward through the soil and contaminate
groundwater. See Figure 4.
As free product is transported through
the soil matrix, it coats and attaches to soil
particles. Residual contamination results from
the constituents that remain after other
constituents have vaporized or dissolved.
Residual contamination tends to be composed
of the heavier, longer-chained paraffins.
Because of volatilization, dissolution, and
naturally occurring biodegradation, the
composition of constituents at a particular site
varies with the passage of time. For example,
at the site of an older release, constituents
such as BTEX may be absent from the
contaminated soil but present in the
groundwater. In fact, over time, the residual
soil contamination from a gasoline spill may
resemble constituents from a fuel oil spill.
Older spills in nonporous soils can, however,
retain unweathered pockets of free product.
In these cases, constituents such as BTEX may
be present at concentrations similar to those
found at a new spill.

Intentionally Blank Page

Measuring the presence of contamination
is an important step in understanding the
potential health effects resulting from gasoline
exposure. Because toxicological research is
usually performed on one chemical at a lime
to establish a discernible cause-and-effect
relationship, little is known about the health
effects from exposure to gasoline (a mixture
of chemicals). However, the health effects of
benzene exposure have been widely studied.
A gap exists between health effects
information, which is typically based on one
component of gasoline (benzene), and
exposure data, which is commonly generated
by field methods that measure groups of
compounds, not individual compounds. This
problem can be solved by either sampling for
benzene or making assumptions about the
relative fraction of benzene in the total
measured compounds. Some common
methods for measuring gasoline and selected
gasoline constituents are mentioned below.
Their expected uses and limitations for
understanding health effects associated with
vapor or water contamination are also
Because gasoline is made up of hundreds
of different hydrocarbon components,
sampling and analyzing for each of the
compounds is impractical. One common
approach is to sample for groups of
petroleum hydrocarbons such as total organic
vapors (TOVs). Tests which measure TOVs
are sensitive to the part per million (ppm)
level and are useful for identifying
contamination. If hydrocarbons are detected
in a vapor or water sample, contamination is
present. However, false negative readings are
possible with these tests; if nothing is
detected, contamination could still be present
in significant concentrations. If low levels of
contamination are suspected but not detected
in a TOV reading, then instruments that can
measure individual compounds should be
In one situation, a test that measures
groups of constituents may give a positive
reading even though contamination is not
present: this occurs when the test detects
methane and not TOVs. Methane can come
from a variety of sources such as sewer lines,
septic fields, and decaying organic materials.
If methane is detected, petroleum
contamination may or may not be present.
(Biodegration of hydrocarbons also produces
high concentrations of methane.) Other
sensors not sensitive to methane or filters that
remove the methane can be used where
methane is suspected to be causing false
positive test results.
Instruments such as the flame ionization
detector (FID), photo ionization detector
(PID), and a TOV colorimetric tube are
widely used to detect organic vapors in
basements. These methods can also be used
above a confined headspace to measure
contamination in water. The Hanby method
also measures contamination in water. The
description and performance of each of these
instruments is described in detail in Field
Measurements: Dependable Data When You
Need It (EPA/530/UST-901003). Minimum
concentrations detected with these instruments
are a function of soil, water, compounds
originally present, holding time, etc.
Although readings from these instruments are
sometimes expressed as benzene equivalents,
measurements of groups of compounds have
no direct correlation with the actual benzene
Volatile compounds are among the most
mobile and toxic constituents of gasoline.
Therefore, they are monitored frequently
around an UST release site. It is possible to
roughly estimate the amount of benzene
present in a TOV reading in air or water
from the total concentration reading.
Benzene is generally less than 0.1 percent
of the total amount of vapors present in a
fresh gasoline release. As the spill ages, the
benzene fraction of the vapor drops. If
benzene-specific vapor measurements are
unavailable, then the 0.1 percent fraction can
be used as an upper bound of the benzene
When measuring water samples, the
benzene fraction is more variable (i.e., from 5

to 100 percent). However, if hydrocarbons
are detected by any of the methods that
measure groups of compounds, the water is
likely to have benzene concentrations above
acceptable health protective levels. In these
cases, use of the water should be suspended
until benzene-specific tests can be conducted.
When you know or suspect people are
being exposed to low levels of contamination,
specific compounds such as benzene should
be measured. For example, testing for
specific compounds should be undertaken
when an old spill is discovered to have
contaminated drinking water supplies or free
product is under buildings emitting vapors.
Specific measurements are also critical in
determining when people may safely re-enter
buildings or re-use drinking water supplies
that were previously contaminated.
The portable gas chromatograph (GC) and
compound-specific colorimetric tubes are two
common field instruments that can measure
benzene and other gasoline constituents.
Other agencies and programs may use other
compound-specific devices, but they will not
be discussed in this document. More
information about the GC and colorimetric
tubes can also be found in Field
Measurements: Dependable Data When You
Need It.
It is important to know the detection
limits that you can achieve with a given
sampling approach. Detection limits for an
analytical test method indicate the smallest
amount of constituents that can be measured
using that technique. Because human health
can be affected by low levels of
contamination, the analytical methods used
for determining when a site does not present
a health risk must be capable of measuring
the level that can be harmful.
Instruments that measure groups of
petroleum hydrocarbons cannot detect the
low levels of benzene considered to pose a
health risk. Low levels of benzene cannot be
measured with these instruments even if
benzene vapors are the only vapors present.
On the other hand, if contamination is
detected with a group-measurement
instrument, it is likely that benzene is
present. Analytical methods for measuring
groups of compounds and individual
compounds are listed in Exhibit 1.
The Lower Detection Limits (LDLs) are
presented for each analytical method listed in
Exhibit 1. LDLs for individual testers,
laboratories, and analysts may vary from
those presented in Exhibit 1 for a variety .of
reasons: (1) the presence of other
contaminants may interfere with the testing
method; (2) the LDLs often vary among
different instrument manufacturers; (3) the
skill of the technician conducting the test is
variable; and, (4) the efficiency of the
equipment (e.g., a purge and trap apparatus)
can affect the detection limits. Sample holding
times and preservation techniques also
dramatically influence the ability of a
technique to detect low levels of

Exhibit 1. Methods for Measuring Gasoline Constituents
Lower Detection Limits
(LDLs) For Gasoline

J Measuring
/ Device
/ Water
/ Vapor
/ Compounds
/ Measured


10 -100 ppm


Colorimetric Tube


GC w/ VOA bottle

Drager Liquid
Colorimetric Tube
0.5 ppm

Benzene or
Hanby Method
'J' -> ' ' ^ / '
0.1 ppm



1-10 ppm

1-10 ppm
Colorimetric Tube

.5 ppm

GC TO -14
.3 ppb

EPA 418.1
1-50 ppm

Total Petroleum

EPA 8020
2-250 ppb
' ^ - *
EPA 8240
5-625 ppb

EPA 624 & 1624
5 ppb


EPA 602
2 ppb


Thin Layer Chroma-
10 -100 ppm

Total Petroleum
* For explanation of field procedures see EPA's Field Measurements: Dependable Data When You Need It.
E-3 = Not Applicable

Intentionally Blank Page

Understanding the potential health effects
associated with exposure to a contaminant
involves discovering who may be exposed,
how they may be exposed, and how long the
exposures may last. Individuals react
differently to chemical exposures depending
on their age and health. In addition,
different effects may occur depending on
whether a chemical is ingested or inhaled and
the duration of exposure.
In only a very few cases are the factors
affecting exposure (i.e., who is exposed, the
exposure frequency and duration, and the
concentration of chemicals at the point where
the person is exposed) well understood.
More often than not, the assessment of
exposure involves estimating many, if not all,
of these factors. The closer the actual
exposure agrees with the predicted exposure,
the better an expert can predict if exposed
individuals are at risk. Greater reliability and
accuracy in the exposure estimates will allow
more reliable and accurate health risk
For simplicity, exposures are usually
assessed separately for each chemical and for
each exposure route. In reality, however,
people may be exposed to more than one
chemical at a time. To estimate health effects
from multiple exposures, risks from
carcinogens are generally considered additive;
noncarcinogenic health effects from chemicals
exerting similar types of effects are also
considered additive.
In identifying "populations at risk," one
needs to consider riot only the location of the
population relative to the spill but also the
activity patterns of its members. Although
people who live or work closest to a spill are
likely to be exposed to the highest
contaminant concentrations, people farther
from a spill may experience more cumulative
exposure over longer periods of time because
they cannot detect contamination through
taste or smell. Also, it is important to know
the age and health status of the exposed
individuals. Children, because of their body
weight, are often at higher risk than adults.
The sick and the elderly are also sensitive
The primary ways that people may be
exposed are obvious for the most part. At
the site, people may come in direct contact
with contaminated soil or water or may
inhale the volatile substances emitted from
the petroleum product. People may inhale
vapors that have entered a nearby building,
ingest contaminants in contaminated drinking
water, or inhale volatile components released
from contaminated water during showering.
Unlikely as it seems, exposures during
showering are often equivalent to those
associated with drinking the water.
It is important to consider all of the ways
people may be exposed. For example, a
person at a business may be exposed only by
drinking contaminated water. In contrast, a
person at a residence may be drinking the
water, inhaling contaminants that volatilize
from the water while showering, and inhaling
product vapors that have directly entered the
building. Therefore, the overall exposure to
the resident in this case is likely to be much
higher. Field staff should also be aware of
other sources of benzene in the home. For
example, tobacco smoke, paints, adhesives,
and lingering automotive exhaust from an
attached garage can contribute to the total
benzene loading.
In estimating exposures, it is also
important to determine how long the
exposure is expected to last. For example, if
vapors have entered a structure, it is
important to consider whether the people
inside will be exposed for 8 hours a day for
5 days of the week (40 hours per week) or,
as in the case of young children at home,
exposed for possibly 24 hours a day for 7
days a week (168 hours a week)—a greater
than four-fold increase in exposure. Whether
the structure is a year-round residence
(exposure for 52 weeks per year) or a
vacation rental (exposure for 2 weeks per

year)-a difference of 26 times—should also
be considered.
The health effects information presented
later in this document is accompanied by
indicators of exposure time. Considering the
duration of exposure is critical when
evaluating the likely adverse health effects
associated with a particular contaminant
concentration. For evaluating exposures to
carcinogenic substances, it is important to
remember that any additional exposure to the
substance increases the likelihood of
developing cancer. In contrast, when
evaluating exposures to noncarcinogenic
substances, it may be possible to tolerate
higher concentrations of the substance in
some cases if the exposure is for a shorter
period of time.

Site-specific constituent and exposure
information can be combined with an
estimate of a chemical's toxicity to evaluate •
the potential health effects of exposure. The
types of health effects associated with
exposure to gasoline and one of its
constituents, benzene, are summarized in
Exhibits 2, 3, and 4. These exhibits are
designed to be used along with specific
information collected for a site regarding
contaminant concentrations, potentially
exposed persons, and anticipated types and
lengths of exposure.
Exhibit 2 presents the health effects
associated with the inhalation of gasoline
vapors. Exhibits 3 and 4 present the health
effects associated with ingesting benzene in
water and inhaling benzene vapors,
respectively. A comparable exhibit for
gasoline in drinking water is not provided
because there is little available information on
the health effects of gasoline as a whole
product in drinking water. Information about
dermal exposures is also not provided
because the extent of these exposures is
generally less than exposures by the other
routes and is difficult to determine.
The exhibits provide:
A summary of the concentrations and
durations at which carcinogenic and
noncarcinogenic effects have been
observed, or are predicted to occur, as a
result of exposure;
Legally enforceable occupational
exposure limits published by the
Occupational Safety and Health
Administration (OSHA);
Drinking water standards published by
EPA's Office of Drinking Water;
Detection limits for various methods of
detecting and measuring benzene in air
and water; and
Risk estimates associated with
exposures to other sources of benzene.
Also please note that the information in the
exhibits has been plotted on a logarithmic
scale. Although the scale increments on the
exhibits are equidistant from one another,
each scale increment is ten times greater than
the one below it. Consequently, extrapolation
between points on the scale cannot be
accomplished in the same manner as
extrapolation on a linear scale. Further
explanation of some of the information in the
exhibits is presented below.
Cancer and noncancer health effects. The
information regarding noncancer health effects
was gathered from studies conducted on
laboratory animals and, occasionally, from
observations on humans exposed to the
chemicals in the workplace or by accident.
Potential cancer risks were calculated based
on EPA risk assessment information and
standard assumptions (i.e., adults weigh 70
kilograms, drink 2 liters of water/day, and
breathe 20 cubic meters of air/day), lixe more
the behavior of the population being
evaluated differs from these assumptions, the
more the actual risk of adverse health effects
will differ from the predicted risk. The
assumptions used in the development of the
risk levels presented in the exhibits are for
adults; children may be three to seven times
more sensitive than adults.
OSHA occupational exposure standards.
OSHA exposure standards are designed to
protect workers against excessive exposures in
the workplace. OSHA standards are based
on both health and economic considerations
and may be inappropriate for evaluating
exposures to the general public. These values
are designed for use with a healthy
population of working age to protect against
adverse health effects due to exposures
during an individual's working life (i.e., 40
hours per week for 45 years).
Drinking water standards. Drinking
water standards, also called Maximum
Contaminant Levels or MCLs, are legally
enforceable levels of a chemical allowed in
drinking water. They are provided in the
exhibits as additional information, but, like
OSHA standards, MCLs are not based

Exhibit 2. Health Effects Associated with Inhaling Gasoline Vapors
Gasoline In Air
Health Effects
Mild anesthesia within
30 minutes
after 1*5 minutes
Eye irritation, somef*
distuibance after
^"OSHA 15-min. STEL|
OSHA 8-hr. TWaST""^
300 —^
_ 140-270
1 in 1,000,000
risk ol cancer,
"if exposed'Tyaars."
24 his. a day
1 in 1,000,000
risk of cancer,
if exposed 70 years.
24 hrs. a day
Levels (ppm)
Lower Detection Llimts
Photo ionization
Detector/Hams ionization
Total Organic
Vapors (TOVs)
Scale is logarithmic.
[*) Short Term Exposure Limit (STEL) -15 tlma-wolghtBd averaga exposure not to exceed 500 ppm.
[bj Tims Wolghled Average (TWA) - not to exceed an waraga of 300 ppm over an 8 - hour day.
Averaga concartrallon far workday to which nearly all workers may be exposed without adverse effects.

Exhibit 3. Health Effects Associated with Ingesting Benzene in Water
Benzene In Drinking Water
Health Effects
drinking water
level for adults
Health Advisories are
health protective only for
specific exposure
durations and do not
Exhibit 4. Health Effects Associated with Inhaling Benzene Vapors
Benzene In Air
Health Effects
Estimated fatal inr
5 to 10 minutes'-

Dangerous to life in 30
minutes to 1 hour M
Symptoms of illness in
1 hour Include headache,
dizziness, vomiting
Headache after 1 hourM
Jteadache, drowsiness
after 5 hours fc]
1 fn 100,000 )
risk of cancer
if exposed 55 years.
5 mia/week
11n 10,000
risk of cancer
Bexposad 70 years. J CI
TffiSayrs diys/'weeK" *
1 in 10,000
risk of cancer,
if exposed 70 years,
24 hre. a day
1 in i.ooo.ooo
risk of cancer,
if exposed 7 years,
24 hrs. a day
1 in 1,000,000
_jnskof cancer,
"Tl exposed7fi yeari',*
24 hrs. a day
Levels (ppm)
^-15SHA8-Hr. TWAl3r~-N
1.0 —^
•—""Maan Self-serve Refueilrtg-s
^	0.9
Exposure Level
Mean Auto Interior
Concentration In'
Rush Hour
Mean Concentration In
Indoor Air [oj

Lower Detection Uimts
Benzene Odor Threshold
I Colorimotric Tubes
Gas Chromatograph
Method TO-14
Scale is logarithmic.
[a] Signs of toxicity Include drowsiness, vertigo, delirium, loss of consciousness.
(bJLong term exposure* (generally 14 days or longer) has been associated with leukemia.
[c]	Long tarro exposure (generally 14 days or longer) has been associated with effects on blood-foimlng organs.
(d)	Time Weighted Average (TWA) - not to exceed an average of tppm over an 8 hour day.
[•] In homos or buildings with smokers this average will be 1 ppb higher.	

solely on health-related information. Some
MCLs, such as the one adopted for benzene,
take into account the technical feasibility of
removing the chemical from the water.
Taste and odor thresholds. Taste and
odor thresholds for benzene in air and water
are presented in the exhibits either as a single
number or a threshold range, because odor
and taste thresholds are highly variable due
to differences in individual sensitivities. In
addition, it should be noted that some
gasoline compounds can be tasted and
smelled at much lower concentrations than
benzene. Although gasoline vapors and
product tend to have a readily distinguishable
odor and taste, there are no published
gasoline odor or taste thresholds, because
thresholds are measured for individual
chemicals and not for a mixture of chemicals
such as gasoline.
Comparative risk information. Some
everyday exposures to benzene are presented
in Exhibit 4 — Benzene in Air — to put some
perspective on the extremely low levels that
EPA considers safe for a lifetime exposure.
The comparative risks are not meant to
minimize the risk of benzene from USTs but
to give some perspective on how pervasive
benzene exposure is in our society. The
reader is advised to use caution when
interpreting these comparative risk numbers
because the sample sizes were small in most
studies. Furthermore, the indoor air
concentration is not a formal EPA advisory.
As of September 1991, EPA had not issued
guidance concerning benzene in indoor air.
It is important to remember that the
health effects summarized in the exhibits are
based on particular exposed populations and
particular exposure durations. Other
populations, or even the same population
exposed for other lengths of time, are likely
to react differently.
It should be noted that the exhibits
display the health effects associated only with
the single route of exposure indicated on the
exhibit. That is, effects for ingestion assume
that the person is only being exposed by this
route. If p person is being exposed by more
than one route, it is important to decrease the
allowable concentrations to account for the
multiple exposures. Exposures from
showering are often equivalent to those
associated with drinking the water. Thus, if
exposure is suspected by both drinking and
showering, the allowable benzene
concentrations should be divided by two.
Since the cancer-causing mechanism is
still a mystery, EPA takes the conservative
position that any exposure to a carcinogen
(such as benzene) carries with it a
corresponding risk (albeit very small) of
developing cancer. The risks EPA predicts
are upper bound values; the real risks are
probably much smaller. Typically, EPA
considers cancer risks greater than 1 in 10,000
unacceptable. A risk level between 1 in
10,000 and 1 in 1,000,000 is (typically selected
as the acceptable limit for cancer risks,
depending upon the circumstances.
Carcinogenic effects usually occur from
exposure to lower doses over longer periods
of time relative to noncarcinogenic effects.
Consequently, exposure levels developed to
protect against carcinogenic effects are usually
protective against the noncarcinogenic effects
as well.
Gasoline is a suspected human carcinogen
because it contains benzene, a known
carcinogen. Exposure, even at low levels,
may result in the development of cancer. As
exposure concentrations increase, it is also
possible that effects other than cancer can
occur, even if exposure duration is short.
These noncancer effects include headache;
nausea; drowsiness; skin, eye, and throat
irritation; loss of reflexes; and liver and
kidney damage. Inhalation of extremely high
concentrations of gasoline can cause loss of
consciousness, coma, and even sudden death.
Over a number of years, inhalation of vapors
can lead to severe blood damage
(hemorrhaging and low blood cell levels),
chromosomal alterations, or cerebral

Benzene is a known human carcinogen,
capable of causing cancer at low levels of
exposure for long periods of time. Benzene
can enter the body through ingestion of
contaminated water, inhalation of
contaminated vapor, or through the skin.
Noncancer effects include dizziness, headache,
nausea, vomiting, skin irritation, and central
nervous system effects. Exposure over a
longer period of time may result in severe
damage to blood-forming organs, leukemia,
nerve damage, or paralysis. Studies have
indicated that benzene adversely affects the
immune system.
epidemiological studies for predicting the
potential health effects likely to occur in
humans as a result of future exposure
involves uncertainty and requires professional
judgment. Health-related guidance and
exposure standards developed by EPA and
other government agencies, such as the
Department of Labor, are based on
professional interpretation of the available
toxicity data. Many times the guidelines
developed by differing agencies are in
agreement, but occasionally they are not.
Some of the differences in the guidelines are
based on differences in the purpose and
assumptions used in their development.
Other differences are the result of differing
professional judgments regarding uncertain
Using toxicological information gathered
from laboratory animal studies and

Hari, R.V.; C J. Dupuy; and D.R. Brown, Action Level for Methyl Tertiary Butyl Ether
(MTBE) in Drinking Water. Connecticut Department of Health Services, Hartford, CT.
U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. 1989.
UST Inspectors Safety and Health Manual. Washington, D.C.: U.S. Government Printing Office.
U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. 1986.
Test Methods for Evaluating Solid Waste, Vol 1A. Washington, D.C.: U.S. Government Printing
U.S. Environmental Protection Agency, Office of Underground Storage Tanks. 1990. Field
Measurements: Dependable Data When You Need It. Washington, D.C.: U.S. Government
Printing Office.
Wallace, L. 1990. Major sources of exposure to benzene and other volatile organic chemicals,
Risk Analysis 10: 59-64.
U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. 1989.
UST Inspectors Safety and Health Manual. Washington, D.C.: U.S. Government Printing Office.
U.S. Environmental Protection Agency, Office of Emergency and Remedial Response. 1989.
Risk Assessment Guidance for Superfund 1: Human Health Evaluation Manual.
Northeast States for Coordinated Air Use Management. 1989. Evaluation of the Health Effects
from Exposure to Gasoline and Gasoline Vapors. Final Report.
U.S. Environmental Protection Agency, Strategies and Air Standards Division. 1978.
Assessment of Gasoline Toxicity.
U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office. 1984.
Health Effects Assessment for Benzene, EPA 540/1-86-037. Cincinnati, Ohio.
U.S. Environmental Protection Agency, Office of Drinking Water. 1985. Drinking Water
Criteria Document for Benzene (Final Draft).
U.S. Public Health Service. Agency for Toxic Substances and Disease Registry. 1989.
Toxicological Profile for Benzene. ATSDR/TP-8803.