Public Health Statement for Cyanide
CAS#: 74-90-8; 143-33-9; 151-50-8; 592-01-8; 544-92-3; 506-61-6; 460-19-5; 506-77-4
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This Public Health Statement is the summary chapter from the Toxicological Profile for Cyanide. It is one in a series of Public Health Statements about hazardous substances and their health effects. A shorter version, the ToxFAQs™, 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 1-888-422-8737.
This public health statement tells you about cyanide and the effects of exposure to it.
The Environmental Protection Agency (EPA) identifies the most serious hazardous waste sites in the nation. These sites are then placed on the
National Priorities List (NPL) and are targeted for
long-term federal clean-up activities. Cyanide has
been found in at least 471 of the 1,662 current or
former NPL sites. Although the total number of
NPL sites evaluated for this substance is not known,
the possibility exists that the number of sites at
which cyanide is found may increase in the future
as more sites are evaluated. This information is
important because these sites may be sources of
exposure and exposure to this substance may harm
When a substance is released either from a large
area, such as an industrial plant, or from a container,
such as a drum or bottle, it enters the environment.
Such a release does not always lead to exposure.
You can be 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
If you are exposed to cyanide, many factors will
determine whether you will 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 any other chemicals you are
exposed to and your age, sex, diet, family traits,
lifestyle, and state of health.
What are cyanides?
Cyanide is a chemical group consisting of one atom
of carbon connected to one atom of nitrogen by
three molecular bonds (C≡N) and cyanides are
compounds (substances formed by the joining of
two or more atoms) that contain a cyanide group
(typically shown as CN). Cyanides can both occur
naturally or be man-made and many are powerful
and rapid-acting poisons. Hydrogen cyanide
(HCN), which is a gas, and the simple cyanide salts
(sodium cyanide and potassium cyanide) are
common examples of cyanide compounds. Certain
bacteria, fungi, and algae can produce cyanide, and
cyanide is found in a number of foods and plants.
In certain plant foods, including almonds, millet
sprouts, lima beans, soy, spinach, bamboo shoots,
and cassava roots (which are a major source of food
in tropical countries), cyanides occur naturally as
part of sugars or other naturally-occurring
compounds. However, the edible parts of plants
that are eaten in the United States, including tapioca
which is made from cassava roots, contain relatively
low amounts of cyanide.
Many of the cyanides in soil and water come from
industrial processes. The major sources of cyanides
in water are discharges from some metal mining
processes, organic chemical industries, iron and
steel plants or manufacturers, and publicly owned
wastewater treatment facilities. Other cyanide
sources include vehicle exhaust, releases from
certain chemical industries, burning of municipal
waste, and use of cyanide-containing pesticides.
Much smaller amounts of cyanide may enter water
through storm water runoff where road salts are
used that contain cyanide. Cyanide in landfills can
contaminate underground water. Hydrogen
cyanide, sodium cyanide, and potassium cyanide are
the forms of cyanide most likely to be in the
environment as a result of industrial activities.
Hydrogen cyanide is a colorless gas with a faint,
bitter, almond-like odor. Sodium cyanide and
potassium cyanide are both white solids with a
slight, bitter, almond-like odor in damp air.
Cyanide salts and hydrogen cyanide are used in
electroplating, metallurgy, organic chemicals
production, photographic developing, manufacture
of plastics, fumigation of ships, and some mining
processes. Hydrogen cyanide has also been used in
gas-chamber executions and as a war gas.
Chlorination of water contaminated with cyanide
produces the compound cyanogen chloride. Four
incidents of cyanide in soil resulted from disposal of
cyanide-containing wastes in landfills and use of
cyanide-containing road salts.
Thiocyanates are a group of compounds formed
from a combination of sulfur, carbon, and nitrogen.
Thiocyanates are found in various foods and plants;
they are produced primarily from the reaction of
free cyanide with sulfur. This reaction occurs in the
environment (for example, in industrial waste streams that contain cyanide) and in the human
body after cyanide is swallowed or absorbed.
Thiocyanate is the major product formed from
cyanide that passes into the body as the body
attempts to rid itself of cyanide. Although
thiocyanates are less harmful than cyanide in
humans, they are known to affect the thyroid
glands, reducing the ability of the gland to produce
hormones that are necessary for the normal function
of the body.
Ammonium thiocyanate is used in antibiotic
preparations, pesticides, liquid rocket fuels,
adhesives, and matches. It also is used in
photographic processes, to improve the strength of
silks, and as a weed killer.
Ammonium thiocyanate is used in antibiotic preparations, pesticides, liquid
rocket fuels, adhesives, and matches. It also is used in photographic processes,
to improve the strength of silks, and as a weed killer.
Thiocyanates are present in water primarily because
of discharges from coal processing, extraction of
gold and silver, and mining industries.
Thiocyanates in soil result from direct application
of herbicides (weed killers), insecticides, and
rodenticides and from disposal of byproducts from
industrial processes. Less important sources
include release from damaged or decaying tissues of
certain plants, such as mustard, kale, and cabbage.
What happens to cyanide when it enters the environment?
Cyanide enters air, water, and soil from both natural
processes and industrial activities. Airborne
cyanide is generally far below levels that would
cause concern. In air, cyanide is present mainly as
gaseous hydrogen cyanide. A small amount of
cyanide in air is present as fine dust particles. This
dust eventually settles over land and water. Rain and snow help remove cyanide particles from air.
The gaseous hydrogen cyanide is not easily
removed from the air by settling, rain, or snow. The
half-life (the time needed for half of the material to
be removed) of hydrogen cyanide in the atmosphere
is about 1–3 years. Most cyanide in surface water
will form hydrogen cyanide and evaporate.
However, the amount of hydrogen cyanide formed
is generally not enough to be harmful to humans.
Some cyanide in water will be transformed into less
harmful chemicals by microorganisms (plants and
animals of very small size), or will form a complex
with metals, such as iron. The half-life of cyanide
in water is not known. Cyanide in water does not
build up in the bodies of fish.
Cyanides are fairly mobile in soil. Once in soils,
cyanide can be removed through several processes.
Some cyanide compounds in soil can form
hydrogen cyanide and evaporate, whereas some
cyanide compounds will be transformed into other
chemical forms by microorganisms in soil.
Consequently, cyanides usually do not seep into
underground water. However, cyanide has been
detected in underground waters of a few landfills
and industrial waste disposal sites. At the high
concentrations found in some landfill leachates
(water that seeps through landfill soil) and in the
wastes stored in some disposal sites, cyanide
becomes toxic to soil microorganisms. Because
these microorganisms can no longer change cyanide
to other chemical forms, cyanide is able to passes
through soil into underground water.
Less is known about what happens to thiocyanate
when it enters the environment. In soil and water,
thiocyanate is changed into other chemical forms by
microorganisms. This occurs in soil mainly at temperatures up to 86 °F (30 °C). At these
temperatures, thiocyanate in soil does not undergo
much evaporation or sorption (binding to soil).
How might I be exposed to cyanide?
You can be exposed to cyanides by breathing air
and drinking water, touching soil or water
containing cyanide, or eating foods that contain
cyanide. Many plant materials, such as cassava
roots, lima beans, and almonds, naturally contain
low-to-moderate levels of cyanide. The
concentration of hydrogen cyanide in unpolluted air
is less than 0.2 parts of hydrogen cyanide per
million (ppm; 1 ppm is equivalent to 1 part by
volume of hydrogen cyanide in a million parts by
volume of air). The concentration of cyanide in
drinking water ranges from 0.001 to 0.011 ppm
(1 ppm is equivalent to 1 part by weight in 1 million
parts by volume of water) in the United States and
Canada. Cyanogen chloride, which can be formed
in the process of water chlorination, has been found
at concentrations ranging from 0.00045 to
0.0008 ppm in drinking water from 35 U.S. cities.
We do not know how many people in the general
population of the United States are exposed to
significant amounts of cyanide from eating foods
that naturally contain it. Smoking is probably one
of the major sources of cyanide exposure for people
who do not work in cyanide-related industries.
Breathing smoke-filled air during fires also may be
a major source of cyanide exposure. People who
live near hazardous waste sites that contain cyanide
may be exposed to higher amounts of cyanide than
the general population.
Cyanide is used or produced in various occupational
settings where activities include electroplating,
some metal mining processes, metallurgy, metal
cleaning, certain pesticide applications, tanning,
photography and photoengraving, firefighting, and
gas works operations. Cyanide also is used in some
dye and pharmaceutical industries. The National
Occupational Exposure Survey (NOES) has
estimated the numbers of workers potentially
exposed to the following cyanides: 4,005 to
hydrogen cyanide; 66,493 to sodium cyanide;
64,244 to potassium cyanide; 3,215 to potassium
silver cyanide; 3,606 to calcium cyanide; 22,339 to
copper (I) cyanide; and 1,393 to cyanogen chloride.
You can be exposed to thiocyanate in the same
ways that you can be exposed to cyanide. Exposure
to cyanide will expose you to thiocyanate because
your body changes toxic cyanide to the much less
toxic thiocyanate. Many foods (plants, dairy
products, meat) contain thiocyanate. People who
work in cyanide-related industries, such as the
manufacture of electronic computing equipment,
commercial printing, photographic processes,
hospitals, production of adhesives, and construction
and furniture manufacture, may be exposed to
thiocyanate. No information is available about the
concentrations of thiocyanate in unpolluted air or
drinking water. We do not know how many people
in the general U.S. population are exposed to
significant amounts of thiocyanate from eating
foods that contain thiocyanate. People who smoke
or breathe tobacco smoke in the environment can be
exposed to high levels of thiocyanate. People who
live near hazardous waste sites that contain
thiocyanate potentially can be exposed to higher
amounts of thiocyanate compared with nonsmokers
in the general population. The National Occupational Exposure Survey (NOES) estimates
that 90,599 workers potentially are exposed to
How can cyanide enter and leave my body?
Cyanide can enter your body if you breathe air, eat
food, or drink water that contains it. Cyanide can
enter your body through the skin, but this may occur
only in people who work in cyanide-related
industries without adequate protective gear. You
can be exposed to contaminated water, air, or soil at
hazardous waste sites. Once it is in your lungs or
stomach, cyanide can quickly enter the bloodstream.
Some of the cyanide is changed to thiocyanate,
which is less harmful and leaves the body in the
urine. A small amount of cyanide is converted in
the body to carbon dioxide, which leaves the body
in the breath. At low levels of exposure to cyanide
compounds, most of the cyanide and its products
leave the body within the first 24 hours after
exposure. The way cyanide enters and leaves the
body is similar in people and animals.
How can cyanide affect my health?
Scientists use many tests to protect the public from
harmful effects of toxic chemicals and to find ways
for treating persons who have been harmed.
One way to learn whether a chemical will harm
people is to determine how the body absorbs, uses,
and releases the chemical. For some chemicals,
animal testing may be necessary. Animal testing may also help identify health effects such as cancer
or birth defects. Without laboratory animals,
scientists would lose a basic method for getting
information needed to make wise decisions that
protect public health. Scientists have the
responsibility to treat research animals with care
and compassion. Scientists must comply with strict
animal care guidelines because laws today protect
the welfare of research animals.
Exposure to small amounts of cyanide can be
deadly regardless of the route of exposure. The
severity of the harmful effects depends in part on
the form of cyanide, such as hydrogen cyanide gas
or cyanide salts. Exposure to high levels of cyanide
for a short time harms the brain and heart and can
even cause coma and death. Cyanide produces
toxic effects at levels of 0.05 milligrams of cyanide
per deciliter of blood (mg/dL) or higher, and deaths
have occurred at levels of 0.3 mg/dL and higher (a
deciliter equals 100 milliliters). People who
breathed 546 ppm of hydrogen cyanide have died
after a 10-minute exposure; 110 ppm of hydrogen
cyanide was life-threatening after a 1-hour
exposure. People who eat small amounts of cyanide
compounds in a short time may die unless they
quickly receive antidote therapy.
Some of the first indications of cyanide poisoning
are rapid, deep breathing and shortness of breath,
followed by convulsions (seizures) and loss of
consciousness. These symptoms can occur rapidly,
depending on the amount eaten. The health effects
of large amounts of cyanide are similar, whether
you eat, drink, or breathe it; cyanide uptake into the
body through the skin is slower than these other
types of exposure. Skin contact with hydrogen
cyanide or cyanide salts can irritate and produce sores. Workers who breathed in amounts of
hydrogen cyanide as low as 6–10 ppm over a period
of time developed breathing difficulties, chest pain,
vomiting, blood changes, headaches, and
enlargement of the thyroid gland.
Use of cassava roots as a primary food source has
led to high blood cyanide levels in some people in
tropical countries. Some of them suffered harmful
effects to the nervous system, including weakness
of the fingers and toes, difficulty walking, dimness
of vision, and deafness, but chemicals other than
cyanide also could have contributed to these effects.
Cyanide exposure from cassava was linked to poor
functioning and later enlargement of the thyroid
gland; this is because in the body, cyanide is
converted to thiocyanate, which is toxic to the
thyroid gland. These effects have not been seen at
levels of cyanide usually found in foods in the
United States. Cyanide has not been reported to
directly cause reproductive problems in people.
Harmful effects on the reproductive system
occurred in rats and mice that drank water
containing sodium cyanide. Other cyanide effects
in animal studies were similar to those observed in
people. Cyanide has not been reported to cause
cancer in people or animals. EPA has determined
that cyanide is not classifiable as to its human
carcinogenicity (ability to cause cancer in humans).
Vitamin B12, a natural chemical containing cyanide,
is beneficial to your body because it prevents
anemia (iron-poor blood). The cyanide binds in
vitamin B12 so that it does not serve as a source of
cyanide exposure and cannot harm you.
How can cyanide affect children?
This section discusses potential health effects in
humans from exposures during the period from
conception to maturity at 18 years of age.
Like adults, children can be exposed to cyanide by
breathing air, drinking water, touching soil or water,
or eating foods that contain cyanide, but the
amounts are usually low. Breathing second-hand
tobacco smoke is a more important source of
cyanide exposure for children. Serious exposures
can occur when children accidentally eat certain
fruit pits, such as apricot kernels, containing a
cyanide-releasing substance. A high blood level of
thiocyanate is a sign of cyanide exposure in
children, as well as adults. If a pregnant mother is
exposed to cyanide, for example, by exposure to
tobacco smoke, the fetus will be exposed to both
cyanide and thiocyanate crossing the placenta.
Animal studies show that cyanide and thiocyanate
can be transferred into milk and pass to nursing
baby animals, and suggest that this may also occur
Effects reported in exposed children are like those
seen in exposed adults. Children who ate large
quantities of apricot pits, which naturally contain
cyanide as part of complex sugars, had rapid
breathing, low blood pressure, headaches, and
coma, and some died. Cyanide has not been
reported to directly cause birth defects in people.
However, among people in the tropics who eat
cassava root, children have been born with thyroid
disease because of the mothers' exposure to cyanide
and thiocyanate during pregnancy. Birth defects
occurred in rats that ate cassava root diets, and harmful effects on the reproductive system occurred
in rats and mice that drank water containing sodium
How can families reduce the risk of exposure to cyanide?
If your doctor finds that you have been exposed to
cyanide, ask whether your children might also have
been exposed. Your doctor might need to ask your
state health department to investigate.
Families can reduce their exposure to cyanide by
not breathing in tobacco smoke, which is the most
common source of cyanide exposure for the general
population. In the event of a building fire, families
should evacuate the building immediately, because
smoke from burning plastics contains cyanide (and
carbon monoxide). Breathing this smoke can lead
to unconsciousness or death. Cyanide in smoke can
arise from the combustion of certain plastics (e.g.,
polyacryl-amines, polyacrylics, polyurethane, etc.).
Compounds that release cyanide are naturally
present in plants. The amounts are usually low in
the edible portion but are higher in cassava. Pits
and seeds of common fruits, such as apricots,
apples, and peaches, may have substantial amounts
of cyanide-releasing chemicals, so people should
avoid eating these pits and seeds to prevent
accidental cyanide poisoning. Parents should teach
their children not eat fruit pits and seeds. People
should be aware that taking high levels of vitamin C
may increase the danger of cyanide poisoning from
fruit pits, because more cyanide is released from the
Studies have shown that the effects of cyanide are
worse in humans and animals with poor nutrition.
Diets containing adequate amounts of protein
should improve recovery from cyanide exposure
Is there a medical test to determine whether I have been exposed to cyanide?
Blood and urine levels of cyanide and thiocyanate
can be measured, and small amounts of these
compounds are always detectable in blood and urine
because of natural processes. After cyanide
poisoning, increased blood levels of cyanide and
thiocyanate are detectable. Harmful effects can
occur when blood levels of cyanide are higher than
0.05 parts per million (ppm), but some effects can
occur at lower levels. Tissue levels of cyanide can
be measured if cyanide poisoning is suspected.
However, cyanide and thiocyanate are cleared
rapidly from the body in urine or exhaled breath; for
that reason, blood measurements are only useful for
detecting recent exposure. A bitter, almond-like
odor in the breath may alert a physician that a
person was exposed to cyanide, but this is not
always found. In general, if cyanide exposure is
suspected, treatment should be started immediately
without waiting for the results of blood cyanide
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. The EPA, the
Occupational Safety and Health Administration
(OSHA), and the Food and Drug Administration
(FDA) are some federal agencies that develop
regulations for toxic substances. Recommendations
provide valuable guidelines to protect public health,
but cannot be enforced by law. The Agency for
Toxic Substances and Disease Registry (ATSDR)
and the National Institute for Occupational Safety
and Health (NIOSH) are two federal organizations
that develop recommendations for toxic substances.
Regulations and recommendations can be expressed
as "not-to-exceed" levels, that is, levels of a toxic
substance in air, water, soil, or food that do not
exceed a critical value that is usually based on
levels that affect animals; they are then adjusted to
levels that will help protect humans. Sometimes
these not-to-exceed levels differ among federal
organizations because they used different exposure
times (an 8-hour workday or a 24-hour day),
different animal studies, or other factors.
Recommendations and regulations are also updated
periodically 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 cyanide
include the following:
EPA sets regulations for the amount of cyanide
allowed in drinking water. The highest amount allowed is 200 micrograms of cyanide per liter of
water (μg/L or 0.2 ppm). EPA also sets limits for
amounts of hydrogen cyanide in stored foods that
have been treated with cyanide to control pests.
The maximum amount allowed on citrus fruits is
50 ppm. EPA also requires industries to report
spills of 1 pound or more of potassium silver
cyanide and 10 pounds or more of hydrogen
cyanide, potassium cyanide, sodium cyanide,
calcium cyanide, or copper cyanide.
OSHA sets levels of cyanide that are allowable in
workplace air. The permissible exposure limit for
hydrogen cyanide (HCN) and most cyanide salts is
10 ppm or 11 milligrams of cyanide per cubic meter
of air (mg/m3) averaged over an 8-hour workday
and 40-hour workweek. NIOSH sets guidelines
(recommended exposure limits or RELs) for
chemicals in workplace air. The short-term REL
for hydrogen cyanide is 4.7 ppm or 5 mg/m3,
averaged over 15 minutes and not to be exceeded at
any time in the workday. There is a 10-minute
ceiling limit for most cyanide salts of 4.7 ppm or
5 mg/m3. NIOSH also determines levels that are
immediately dangerous to life and health (IDLH) if
a worker is exposed for more than half an hour.
IDLH levels are 50 ppm for hydrogen cyanide or
25 mg/m3 as cyanide for most cyanide salts.
Agency for Toxic Substances and Disease Registry (ATSDR). 2006. Toxicological profile for Cyanide. 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.