Public Health Statement for Sulfur Trioxide and Sulfuric Acid
Spanish: Anhídrido sulfúrico y Ácido sulfúrico
CAS#: Sulfur Trioxide 7446-11-9; Sulfuric Acid 7664-93-9
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This Public Health Statement is the
summary chapter from the Toxicological
Profile for Sulfur Trioxide and Sulfuric Acid. It is one
in a series of Public Health Statements about hazardous substances
and their health effects. A shorter version, the ToxFAQsTM,
is also available. This information is important because this
substance may harm you. The effects of exposure to any hazardous
substance depend on the dose, the duration, how you are exposed,
personal traits and habits, and whether other chemicals are
present. For more information, call the ATSDR Information
Center at 1-800-232-4636.
This public health statement tells you
about sulfur trioxide and sulfuric acid and the effects of
The Environmental Protection Agency (EPA)
identifies the most serious hazardous waste sites in the nation.
These sites make up the National Priorities List (NPL) and
are the sites targeted for long-term federal cleanup.
Sulfur trioxide and sulfuric acid have been found in at least
47 of the 1,467 current or former NPL sites. As more
sites are evaluated, the sites with sulfur trioxide or sulfuric
acid may increase. This is important because exposure
to these substances may harm you and because these sites may
be sources of exposure.
When a substance is released from a large
area, such as an industrial plant, or from a container, such
as a drum or bottle, it enters the environment. This
release does not always lead to exposure. You are exposed
to a substance only when you come in contact with it.
You may be exposed by breathing, eating, or drinking the substance
or by skin contact.
If you are exposed to sulfur trioxide
or sulfuric acid, many factors determine whether you'll be
harmed. These factors include the dose (how much), the
duration (how long), and how you come in contact with it.
You must also consider the other chemicals you're exposed
to and your age, sex, diet, family traits, lifestyle, and
state of health.
What are sulfur trioxide and sulfuric acid?
Sulfur trioxide is generally a colorless
liquid but can also exist as ice- or fiber-like crystals or
as a gas. When sulfur trioxide is exposed to air, it
rapidly takes up water and gives off white fumes. It
combines with water, releasing considerable heat while forming
sulfuric acid. It also reacts violently with some metal
oxides. Sulfur trioxide is also called sulfuric oxide
and sulfuric anhydride. It is used as an intermediate
in the production of sulfuric acid, other chemicals, and explosives.
Sulfur trioxide is unlikely to exist in the environment except
for very short periods when it may be present in the air as
a gas. In the air, sulfur trioxide can be formed slowly
from sulfur dioxide. Once formed, sulfur trioxide will
react with water in the air to form sulfuric acid. Both
sulfur dioxide and sulfuric acid are more likely to be found
in air than sulfur trioxide. If you are interested in
learning more about sulfur dioxide, the Agency for Toxic Substances
and Disease Registry has developed a separate profile about
Sulfuric acid is a clear, colorless,
oily liquid that is very corrosive. An odor threshold
of sulfuric acid in air has been reported to be 1 milligram
per cubic meter of air (mg/m3). If you are
exposed to concentrated sulfuric acid in air, your nose will
be irritated and it may seem like sulfuric acid has a pungent
odor. When concentrated sulfuric acid is mixed with
water, the solution gets very hot. Concentrated sulfuric
acid can catch fire or explode when it comes into contact
with many chemicals including acetone, alcohols, and some
finely divided metals. When heated it emits highly toxic
fumes, which include sulfur trioxide. It is also called
sulphine acid, battery acid, and hydrogen sulfate. More
sulfuric acid is produced in the United States than any other
chemical. It is used in the manufacture of fertilizers,
explosives, other acids, and glue; in the purification of
petroleum; in the pickling of metal; and in lead-acid batteries
(the type commonly used in motor vehicles). Sulfuric
acid can be found in the air as small droplets or it can be
attached to other small particles in the air.
Fuming sulfuric acid, also called oleum,
is a solution of 10ï¿½70% sulfur trioxide in sulfuric acid.
Oleum is the form of sulfuric acid that is often shipped in
What happens to sulfur trioxide and sulfuric
acid when they enter the
Much of the sulfuric acid in the air
is formed from sulfur dioxide released when coal, oil, and
gas are burned. The released sulfur dioxide slowly forms
sulfur trioxide, which reacts with water in the air to form
sulfuric acid. Sulfuric acid dissolves in the water
in air and can remain suspended for varying periods of time;
it is removed from the air as rain. Sulfuric acid in
rain contributes to the formation of acid rain. Sulfuric
acid in water separates to form hydrogen ions and sulfate.
The ability of sulfuric acid to change the acidity (pH) of
water is dependent on the amount of sulfuric acid and the
ability of other substances in the water to neutralize the
hydrogen ions (buffering capacity).
How might I be exposed to sulfur trioxide and sulfuric acid?
You may be exposed to sulfur trioxide
or sulfuric acid at your job if you work in the chemical or
metal plating industry; if you produce detergents, soaps,
fertilizers, or lead-acid batteries; or if you work in printing
and publishing, or photography shops. Because sulfur
trioxide forms sulfuric acid when it contacts the moist surfaces
of your respiratory tract or your skin, the effects caused
by sulfur trioxide and sulfuric acid are similar. In
occupational settings, breathing small droplets of sulfur
trioxide or sulfuric acid or touching it with your skin are
the most likely ways you would be exposed to sulfuric acid.
According to estimates from a survey conducted by the National
Institute for Occupational Safety and Health (NIOSH) more
than 56,103 U.S. workers may be exposed to sulfur trioxide,
and more than 775,348 U.S. workers may be exposed to sulfuric
acid. However, this survey used estimates from small
samples, so the number of workers exposed to sulfur trioxide
and sulfuric acid may be overestimated.
You may also be exposed to sulfuric acid
by breathing outdoor air containing this compound. As
mentioned before, sulfuric acid droplets can form in the air
when sulfur dioxide is released from the burning of coal,
oil, and gas. This released sulfur dioxide slowly forms
sulfur trioxide and then reacts with water in the air to form
sulfuric acid. While sulfuric acid could be present
in the air during episodes of high pollution, all air pollution
is not due to sulfuric acid contamination. The effects
of other pollutants in air may be of greater concern to the
general population. Likewise, there are relatively few
sulfuric acid air pollution episodes today.
People living near hazardous waste sites
that contain sulfuric acid are at greater risk of exposure
by breathing contaminated air than is the general public.
For these people, spending time outdoors, especially exercising,
could increase their risks of being exposed.
You can also be exposed to sulfuric acid
when you touch the material that forms on the outside of your
car battery. Sulfuric acid is formed when some toilet
bowl cleaners mix with water. Therefore, if these products
touch skin or are accidentally swallowed, you could be exposed
to sulfuric acid. When you cut onions a chemical called
propanethiol S-oxide is released into the air. When
this chemical reaches your eyes, it reacts with the water
in your eyes to form sulfuric acid, which causes your eyes
to water. People have also been exposed following accidental
spills of sulfuric acid or oleum. These accidents occurred
more frequently at a site than while the substances were being
How can sulfur trioxide and sulfuric acid enter and leave my body?
If you breathe in sulfur trioxide, small
droplets of sulfuric acid will form when the sulfur trioxide
contacts water. Small droplets of sulfuric acid may
also enter the respiratory tract when you breathe. Where
the droplets will deposit in the respiratory tract depends
on their size and how deeply you are breathing. Smaller
droplets will deposit deeper into the lung. If you breathe
through your mouth, more droplets will deposit in your lungs
than if you breathe only through your nose. Extra sulfur
dioxide breakdown products are excreted in the urine.
Sulfuric acid causes its effects by direct
action on tissues that it touches. With the exception
of how sulfuric acid droplets deposit in the lungs, how sulfur
trioxide and sulfuric acid enter and leave your body does
not alter the effects of sulfuric acid.
How can sulfur trioxide and sulfuric acid affect my health?
To protect the public from the harmful
effects of toxic chemicals and to find ways to treat people
who have been harmed, scientists use many tests.
One way to see if a chemical will hurt
people is to learn how the chemical is absorbed, used, and
released by the body; for some chemicals, animal testing may
be necessary. Animal testing may also be used to identify
health effects such as cancer or birth defects. Without
laboratory animals, scientists would lose a basic method to
get information needed to make wise decisions to protect
public health. Scientists have the responsibility to
treat research animals with care and compassion. Laws
today protect the welfare of research animals, and scientists
must comply with strict animal care guidelines.
Sulfuric acid and other acids are very
corrosive and irritating and cause direct local effects on
the skin, eyes, and respiratory and gastrointestinal tracts
when there is direct exposure to sufficient concentrations.
Breathing sulfuric acid mists can result in tooth erosion
and respiratory tract irritation. Drinking concentrated
sulfuric acid can burn your mouth and throat, and it can erode
a hole in your stomach; it has also resulted in death.
If you touch sulfuric acid, it will burn your skin.
If you get sulfuric acid in your eyes, it will burn your eyes
and cause them to water. The term "burn" used in these
sections refers to a chemical burn, not a physical burn resulting
from contacting a hot object. People have been blinded
by sulfuric acid when it was thrown in their faces.
Breathing small droplets of sulfuric
acid at levels that might be in the air on a day with high
air pollution may make it more difficult to breathe.
This effect is more likely to occur if you have been exercising
or if you have asthma. This effect may also be more
likely to occur in children than adults. Breathing sulfuric
acid droplets may affect the ability of your respiratory tract
to remove other small particles that you have inhaled.
If you breathe sulfur trioxide, it turns into sulfuric acid
in your upper respiratory tract, and the effects you may experience
will be similar to those of sulfuric acid inhalation.
Studies in people who breathed high concentrations
of sulfuric acid at work have shown an increase in cancers
of the larynx. However, most of the cancers were in
smokers who were also exposed to other acids and other chemicals.
There is no information that exposure to sulfuric acid by
itself is carcinogenic. The carcinogenicity of sulfuric
acid has not been studied in animals. The EPA and the
U.S. Department of Health and Human Services (DHHS) have not
classified sulfur trioxide or sulfuric acid for carcinogenic
effects. Based on very limited human data, the International
Agency for Research on Cancer (IARC) believes that evidence
is sufficient to state that occupational exposure to strong
inorganic acid mists containing sulfuric acid is carcinogenic
to humans. IARC has not classified pure sulfuric acid
for its carcinogenic effects.
How can sulfur trioxide and sulfuric acid affect children?
This section discusses potential health
effects from exposures during the period from conception to
maturity at 18 years of age in humans. Potential effects
on children resulting from exposures of the parents are also
Children may be exposed to sulfur trioxide
and sulfuric acid in the same manner as adults, with the exception
of chemical encounters in the workplace. Sulfur trioxide
is only used in industry as an intermediate in the production
of chemicals such as sulfuric acid and quickly converts to
sulfuric acid when it contacts water in air. Therefore,
children will most likely only be at risk of exposure from
sulfuric acid, not sulfur trioxide. Exposure to sulfuric
acid may occur through skin contact, eye contact, ingestion,
and breathing contaminated air. Sulfuric acid can cause
severe skin burns, it can burn the eyes, burn holes in the
stomach if swallowed, irritate the nose and throat, and cause
difficulties breathing if inhaled.
Exposure to sulfuric acid from accidental
contact with or misuse of sulfuric acid-containing consumer
products is the most likely way your child could be exposed.
Household products that contain sulfuric acid include drain
and toilet bowl cleaners, and some acid car batteries.
The national estimate (derived by United States Consumer Product
Safety Commission, USCPSC) for injuries related to drain cleaners
over a 5-year period ending January 1996 is between 2,800
and 3,150 injuries per year. Inquisitive toddlers may
get into unsealed or improperly stored containers of sulfuric
acid-containing products. Transfer of cleaning agents
containing sulfuric acid into containers not designed for
their storage can allow leakage from the container.
Improper flushing of areas recently cleaned with a sulfuric
acid-containing product can lead to inadvertent skin exposure
to both children and adults.
While younger children are most at risk
from accidental swallowing, skin contact, or eye contact with
sulfuric acid in household products, teenagers might have
jobs in which they may contact sulfuric acid. If teenagers
must use acid cleaners in their jobs or work in car repair
where they may contact car batteries, they might be exposed.
Furthermore, there have been reports of older children using
sulfuric acid-containing solutions as weapons, thereby causing
severe skin damage when intentionally splashed on others.
Small droplets of sulfuric acid may exist
in the outdoor air. You and your children have the greatest
chances of inhaling the compound during times of high air
pollution with sulfuric acid. This may lead to difficulty
breathing. If you live near electrical, metal processing,
or paper processing industries, you may also have a greater
chance of exposure to sulfuric acid. When sulfuric acid
is inhaled into the lungs in the form of small droplets that
exist in air, these droplets are deposited within the lung
and the ability of your respiratory tract to remove other
small, unwanted particles may be decreased. A study
has shown that children can have greater deposition of sulfuric
acid in their lungs than adults due to children's smaller
airway diameters. Also, because children breathe more
air per kilogram of body weight than adults, children may
take in more sulfuric acid when they breathe the same contaminated
air. Increased sensitivity has been witnessed in both
animal studies with young guinea pigs and in human studies
of asthmatic adolescents. This evidence suggests that
children may be more vulnerable than adults to the health
effects associated with breathing sulfuric acid.
No studies examining effects on unborn
children following a mother's exposure to sulfuric acid during
pregnancy were identified in humans. Limited evidence
in animals indicates that sulfuric acid is not a hazard to
unborn children. Birth defects have not been observed
in animals that breathed high levels of sulfuric acid mist.
Exposing pregnant rabbits to sulfuric acid did not significantly
affect the body weights or cause malformations in their offspring.
Again, because sulfuric acid causes adverse effects at its
point of contact with the body, the acid, as such, is not
expected to be absorbed or distributed throughout the body.
Sulfuric acid is not expected to be transported across a mother's
placenta into her developing baby or into breast milk.
Therefore, an exposed mother most likely will not threaten
her unborn or nursing child. Since sulfuric acid's effects
occur at the point of contact, it is not likely that it will
reach a mother's egg or father's sperm. Therefore, parents
exposure to sulfuric acid or sulfur trioxide should not affect
their unborn children.
How can families reduce the risk of exposure to sulfur trioxide and sulfuric acid?
If your doctor finds that you have been
exposed to significant amounts of sulfur trioxide or sulfuric
acid, ask if children may also be exposed. When necessary
your doctor may need to ask your State Department of Public
Health to investigate.
Sulfuric acid is a highly corrosive chemical
that is potentially explosive in concentrated form.
It can cause severe skin burns, can irritate the nose and
throat and cause difficulties breathing if inhaled, can burn
the eyes and possibly cause blindness, and can burn holes
in the stomach if swallowed.
Concentrated sulfuric acid is commonly
used in the United States as a drain and toilet bowl cleaner.
Children and adults have suffered full thickness skin burns
upon accidental contact or intentional assault with sulfuric
acid in this form. Additionally, sulfuric acid is formed
when some toilet bowl cleaners mix with water, so care should
be taken not to breathe associated vapors or splash any liquid
on the skin or in the eyes. All household chemicals
containing sulfuric acid should be stored in their original,
labeled containers, kept in locked cabinets away from children,
kept away from fire, and should be used only for their intended
purposes. The material that forms on the outside of
a car battery is also a source of sulfuric acid and you should
avoid touching it. Wear safety glasses and use chemical
resistant gloves to avoid this type of exposure. Upon
any exposure to sulfuric acid, the contacted body part should
be immediately flushed with plentiful water and then the Poison
Control Center contacted. Keep your Poison Control Center's
number by the phone. If sulfuric acid is spilled in the home,
the local Fire Department should be contacted for assistance
in handling the spill.
When levels of air pollution are high,
families are advised to stay indoors as much as possible and
to avoid exercising outdoors. Families can be aware
of levels of air pollution by paying attention to news bulletins
and air pollution advisories, most of which are issued by
the EPA (Environmental Protection Agency). This is particularly
important for individuals with respiratory conditions and
asthmatic children. Staying indoors during times of
sulfuric acid air pollution will help you avoid breathing
sulfuric acid droplets.
Adults may be occupationally exposed
to sulfuric acid if they work in the chemical or metal plating
industry; produce detergents, soaps, fertilizers, or
lead-acid batteries; or work in printing or publishing, or
photography shops. It is not anticipated that workers
in such industries can expose their families at home (through
their clothing, skin, or breath) to sulfuric acid contacted
Is there a medical test to determine whether I have been exposed to sulfur trioxide and sulfuric acid?
There is no medical test to determine
whether you have been exposed to sulfur trioxide or sulfuric
acid. Breathing in acids, including sulfuric acid, will
increase the acidity of your saliva. Measuring the acidity
of saliva may determine whether you have been exposed
to acid but cannot determine which acid.
What recommendations has the federal government made to protect human health?
The federal government develops regulations
and recommendations to protect public health. Regulations can be enforced by law. Federal agencies that
develop regulations for toxic substances include the Environmental
Protection Agency (EPA), the Occupational Safety and Health
Administration (OSHA), and the Food and Drug Administration
(FDA). Recommendations provide valuable guidelines to
protect public health but cannot be enforced by law.
Federal organizations that develop recommendations for toxic
substances include the Agency for Toxic Substances and Disease
Registry (ATSDR) and the National Institute for Occupational
Safety and Health (NIOSH).
Regulations and recommendations can be
expressed in not-to-exceed levels in air, water, soil, or
food that are usually based on levels that affect animals;
then they are adjusted to help protect people. Sometimes
these not-to-exceed levels differ among federal organizations
because of different exposure times (an 8-hour workday or
a 24-hour day), the use of different animal studies, or other
Recommendations and regulations are also
periodically updated as more information becomes available.
For the most current information, check with the federal agency
or organization that provides it. Some regulations and
recommendations for sulfur trioxide and sulfuric acid include
EPA limits the amount of sulfur dioxide
that can be released into the air. This limits the amount
of sulfur trioxide and sulfuric acid that form from sulfur
dioxide in the air.
OSHA limits the amount of sulfuric acid
that can be present in workroom air to 1 mg/m3.
NIOSH also recommends a time-weighted average limit of 1 mg/m3.
Agency for Toxic Substances and Disease Registry (ATSDR). 1998. Toxicological profile for Sulfur Trioxide and Sulfuric Acid. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
Where can I get more information?
If you have questions or concerns, please contact your community or state health or environmental quality department or:
For more information, contact:
Agency for Toxic Substances and Disease Registry
Division of Toxicology and Human Health Sciences
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO
ATSDR can also tell you the location of occupational and environmental health clinics. These clinics specialize in recognizing, evaluating, and treating illnesses resulting from exposure to hazardous substances.