Cyanide | Public Health Statement (2024)

Public Health Statement for Cyanide

Spanish: Cianuro

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 theNational Priorities List (NPL) and are targeted forlong-term federal clean-up activities. Cyanide hasbeen found in at least 471 of the 1,662 current orformer NPL sites. Although the total number ofNPL sites evaluated for this substance is not known,the possibility exists that the number of sites atwhich cyanide is found may increase in the futureas more sites are evaluated. This information isimportant because these sites may be sources ofexposure and exposure to this substance may harmyou.

When a substance is released either from a largearea, 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 youcome in contact with it. You may be exposed by breathing, eating, or drinking the substance, or byskin contact.

If you are exposed to cyanide, many factors willdetermine whether you will be harmed. Thesefactors 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 areexposed to and your age, sex, diet, family traits,lifestyle, and state of health.

What are cyanides?

Cyanide is a chemical group consisting of one atomof carbon connected to one atom of nitrogen bythree molecular bonds (C≡N) and cyanides arecompounds (substances formed by the joining oftwo or more atoms) that contain a cyanide group(typically shown as CN). Cyanides can both occurnaturally or be man-made and many are powerfuland rapid-acting poisons. Hydrogen cyanide(HCN), which is a gas, and the simple cyanide salts(sodium cyanide and potassium cyanide) arecommon examples of cyanide compounds. Certainbacteria, fungi, and algae can produce cyanide, andcyanide is found in a number of foods and plants.In certain plant foods, including almonds, milletsprouts, lima beans, soy, spinach, bamboo shoots,and cassava roots (which are a major source of foodin tropical countries), cyanides occur naturally aspart of sugars or other naturally-occurringcompounds. However, the edible parts of plantsthat are eaten in the United States, including tapiocawhich is made from cassava roots, contain relativelylow amounts of cyanide.

Many of the cyanides in soil and water come fromindustrial processes. The major sources of cyanidesin water are discharges from some metal miningprocesses, organic chemical industries, iron andsteel plants or manufacturers, and publicly ownedwastewater treatment facilities. Other cyanidesources include vehicle exhaust, releases fromcertain chemical industries, burning of municipalwaste, and use of cyanide-containing pesticides.Much smaller amounts of cyanide may enter waterthrough storm water runoff where road salts areused that contain cyanide. Cyanide in landfills cancontaminate underground water. Hydrogencyanide, sodium cyanide, and potassium cyanide arethe forms of cyanide most likely to be in theenvironment as a result of industrial activities.Hydrogen cyanide is a colorless gas with a faint,bitter, almond-like odor. Sodium cyanide andpotassium cyanide are both white solids with aslight, bitter, almond-like odor in damp air.Cyanide salts and hydrogen cyanide are used inelectroplating, metallurgy, organic chemicalsproduction, photographic developing, manufactureof plastics, fumigation of ships, and some miningprocesses. Hydrogen cyanide has also been used ingas-chamber executions and as a war gas.Chlorination of water contaminated with cyanideproduces the compound cyanogen chloride. Fourincidents of cyanide in soil resulted from disposal ofcyanide-containing wastes in landfills and use ofcyanide-containing road salts.

Thiocyanates are a group of compounds formedfrom a combination of sulfur, carbon, and nitrogen.Thiocyanates are found in various foods and plants;they are produced primarily from the reaction offree cyanide with sulfur. This reaction occurs in theenvironment (for example, in industrial waste streams that contain cyanide) and in the humanbody after cyanide is swallowed or absorbed.Thiocyanate is the major product formed fromcyanide that passes into the body as the bodyattempts to rid itself of cyanide. Althoughthiocyanates are less harmful than cyanide inhumans, they are known to affect the thyroidglands, reducing the ability of the gland to producehormones that are necessary for the normal functionof the body.

Ammonium thiocyanate is used in antibioticpreparations, pesticides, liquid rocket fuels,adhesives, and matches. It also is used inphotographic processes, to improve the strength ofsilks, 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 becauseof discharges from coal processing, extraction ofgold and silver, and mining industries.Thiocyanates in soil result from direct applicationof herbicides (weed killers), insecticides, androdenticides and from disposal of byproducts fromindustrial processes. Less important sourcesinclude release from damaged or decaying tissues ofcertain plants, such as mustard, kale, and cabbage.

What happens to cyanide when it enters the environment?

Cyanide enters air, water, and soil from both naturalprocesses and industrial activities. Airbornecyanide is generally far below levels that wouldcause concern. In air, cyanide is present mainly asgaseous hydrogen cyanide. A small amount ofcyanide in air is present as fine dust particles. Thisdust eventually settles over land and water. Rain and snow help remove cyanide particles from air.The gaseous hydrogen cyanide is not easilyremoved from the air by settling, rain, or snow. Thehalf-life (the time needed for half of the material tobe removed) of hydrogen cyanide in the atmosphereis about 1–3 years. Most cyanide in surface waterwill form hydrogen cyanide and evaporate.However, the amount of hydrogen cyanide formedis generally not enough to be harmful to humans.Some cyanide in water will be transformed into lessharmful chemicals by microorganisms (plants andanimals of very small size), or will form a complexwith metals, such as iron. The half-life of cyanidein water is not known. Cyanide in water does notbuild 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 formhydrogen cyanide and evaporate, whereas somecyanide compounds will be transformed into otherchemical forms by microorganisms in soil.Consequently, cyanides usually do not seep intounderground water. However, cyanide has beendetected in underground waters of a few landfillsand industrial waste disposal sites. At the highconcentrations found in some landfill leachates(water that seeps through landfill soil) and in thewastes stored in some disposal sites, cyanidebecomes toxic to soil microorganisms. Becausethese microorganisms can no longer change cyanideto other chemical forms, cyanide is able to passesthrough soil into underground water.

Less is known about what happens to thiocyanatewhen it enters the environment. In soil and water,thiocyanate is changed into other chemical forms bymicroorganisms. This occurs in soil mainly at temperatures up to 86 °F (30 °C). At thesetemperatures, thiocyanate in soil does not undergomuch evaporation or sorption (binding to soil).

How might I be exposed to cyanide?

You can be exposed to cyanides by breathing airand drinking water, touching soil or watercontaining cyanide, or eating foods that containcyanide. Many plant materials, such as cassavaroots, lima beans, and almonds, naturally containlow-to-moderate levels of cyanide. Theconcentration of hydrogen cyanide in unpolluted airis less than 0.2 parts of hydrogen cyanide permillion (ppm; 1 ppm is equivalent to 1 part byvolume of hydrogen cyanide in a million parts byvolume of air). The concentration of cyanide indrinking water ranges from 0.001 to 0.011 ppm(1 ppm is equivalent to 1 part by weight in 1 millionparts by volume of water) in the United States andCanada. Cyanogen chloride, which can be formedin the process of water chlorination, has been foundat concentrations ranging from 0.00045 to0.0008 ppm in drinking water from 35 U.S. cities.We do not know how many people in the generalpopulation of the United States are exposed tosignificant amounts of cyanide from eating foodsthat naturally contain it. Smoking is probably oneof the major sources of cyanide exposure for peoplewho do not work in cyanide-related industries.Breathing smoke-filled air during fires also may bea major source of cyanide exposure. People wholive near hazardous waste sites that contain cyanidemay be exposed to higher amounts of cyanide thanthe general population.

Cyanide is used or produced in various occupationalsettings where activities include electroplating,some metal mining processes, metallurgy, metalcleaning, certain pesticide applications, tanning,photography and photoengraving, firefighting, andgas works operations. Cyanide also is used in somedye and pharmaceutical industries. The NationalOccupational Exposure Survey (NOES) hasestimated the numbers of workers potentiallyexposed to the following cyanides: 4,005 tohydrogen cyanide; 66,493 to sodium cyanide;64,244 to potassium cyanide; 3,215 to potassiumsilver cyanide; 3,606 to calcium cyanide; 22,339 tocopper (I) cyanide; and 1,393 to cyanogen chloride.

You can be exposed to thiocyanate in the sameways that you can be exposed to cyanide. Exposureto cyanide will expose you to thiocyanate becauseyour body changes toxic cyanide to the much lesstoxic thiocyanate. Many foods (plants, dairyproducts, meat) contain thiocyanate. People whowork in cyanide-related industries, such as themanufacture of electronic computing equipment,commercial printing, photographic processes,hospitals, production of adhesives, and constructionand furniture manufacture, may be exposed tothiocyanate. No information is available about theconcentrations of thiocyanate in unpolluted air ordrinking water. We do not know how many peoplein the general U.S. population are exposed tosignificant amounts of thiocyanate from eatingfoods that contain thiocyanate. People who smokeor breathe tobacco smoke in the environment can beexposed to high levels of thiocyanate. People wholive near hazardous waste sites that containthiocyanate potentially can be exposed to higheramounts of thiocyanate compared with nonsmokersin the general population. The National Occupational Exposure Survey (NOES) estimatesthat 90,599 workers potentially are exposed toammonium thiocyanate.

How can cyanide enter and leave my body?

Cyanide can enter your body if you breathe air, eatfood, or drink water that contains it. Cyanide canenter your body through the skin, but this may occuronly in people who work in cyanide-relatedindustries without adequate protective gear. Youcan be exposed to contaminated water, air, or soil athazardous waste sites. Once it is in your lungs orstomach, cyanide can quickly enter the bloodstream.Some of the cyanide is changed to thiocyanate,which is less harmful and leaves the body in theurine. A small amount of cyanide is converted inthe body to carbon dioxide, which leaves the bodyin the breath. At low levels of exposure to cyanidecompounds, most of the cyanide and its productsleave the body within the first 24 hours afterexposure. The way cyanide enters and leaves thebody is similar in people and animals.

How can cyanide affect my health?

Scientists use many tests to protect the public fromharmful effects of toxic chemicals and to find waysfor treating persons who have been harmed.

One way to learn whether a chemical will harmpeople 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 canceror birth defects. Without laboratory animals,scientists would lose a basic method for gettinginformation needed to make wise decisions thatprotect public health. Scientists have theresponsibility to treat research animals with careand compassion. Scientists must comply with strictanimal care guidelines because laws today protectthe welfare of research animals.

Exposure to small amounts of cyanide can bedeadly regardless of the route of exposure. Theseverity of the harmful effects depends in part onthe form of cyanide, such as hydrogen cyanide gasor cyanide salts. Exposure to high levels of cyanidefor a short time harms the brain and heart and caneven cause coma and death. Cyanide producestoxic effects at levels of 0.05 milligrams of cyanideper deciliter of blood (mg/dL) or higher, and deathshave occurred at levels of 0.3 mg/dL and higher (adeciliter equals 100 milliliters). People whobreathed 546 ppm of hydrogen cyanide have diedafter a 10-minute exposure; 110 ppm of hydrogencyanide was life-threatening after a 1-hourexposure. People who eat small amounts of cyanidecompounds in a short time may die unless theyquickly receive antidote therapy.

Some of the first indications of cyanide poisoningare rapid, deep breathing and shortness of breath,followed by convulsions (seizures) and loss ofconsciousness. These symptoms can occur rapidly,depending on the amount eaten. The health effectsof large amounts of cyanide are similar, whetheryou eat, drink, or breathe it; cyanide uptake into thebody through the skin is slower than these othertypes of exposure. Skin contact with hydrogencyanide or cyanide salts can irritate and produce sores. Workers who breathed in amounts ofhydrogen cyanide as low as 6–10 ppm over a periodof time developed breathing difficulties, chest pain,vomiting, blood changes, headaches, andenlargement of the thyroid gland.

Use of cassava roots as a primary food source hasled to high blood cyanide levels in some people intropical countries. Some of them suffered harmfuleffects to the nervous system, including weaknessof the fingers and toes, difficulty walking, dimnessof vision, and deafness, but chemicals other thancyanide also could have contributed to these effects.Cyanide exposure from cassava was linked to poorfunctioning and later enlargement of the thyroidgland; this is because in the body, cyanide isconverted to thiocyanate, which is toxic to thethyroid gland. These effects have not been seen atlevels of cyanide usually found in foods in theUnited States. Cyanide has not been reported todirectly cause reproductive problems in people.Harmful effects on the reproductive systemoccurred in rats and mice that drank watercontaining sodium cyanide. Other cyanide effectsin animal studies were similar to those observed inpeople. Cyanide has not been reported to causecancer in people or animals. EPA has determinedthat cyanide is not classifiable as to its humancarcinogenicity (ability to cause cancer in humans).

Vitamin B₁₂, a natural chemical containing cyanide,is beneficial to your body because it preventsanemia (iron-poor blood). The cyanide binds invitamin B12 so that it does not serve as a source ofcyanide exposure and cannot harm you.

How can cyanide affect children?

This section discusses potential health effects inhumans from exposures during the period fromconception to maturity at 18 years of age.

Like adults, children can be exposed to cyanide bybreathing air, drinking water, touching soil or water,or eating foods that contain cyanide, but theamounts are usually low. Breathing second-handtobacco smoke is a more important source ofcyanide exposure for children. Serious exposurescan occur when children accidentally eat certainfruit pits, such as apricot kernels, containing acyanide-releasing substance. A high blood level ofthiocyanate is a sign of cyanide exposure inchildren, as well as adults. If a pregnant mother isexposed to cyanide, for example, by exposure totobacco smoke, the fetus will be exposed to bothcyanide and thiocyanate crossing the placenta.Animal studies show that cyanide and thiocyanatecan be transferred into milk and pass to nursingbaby animals, and suggest that this may also occurin humans.

Effects reported in exposed children are like thoseseen in exposed adults. Children who ate largequantities of apricot pits, which naturally containcyanide as part of complex sugars, had rapidbreathing, low blood pressure, headaches, andcoma, and some died. Cyanide has not beenreported to directly cause birth defects in people.However, among people in the tropics who eatcassava root, children have been born with thyroiddisease because of the mothers' exposure to cyanideand thiocyanate during pregnancy. Birth defectsoccurred in rats that ate cassava root diets, and harmful effects on the reproductive system occurredin rats and mice that drank water containing sodiumcyanide.

How can families reduce the risk of exposure to cyanide?

If your doctor finds that you have been exposed tocyanide, ask whether your children might also havebeen exposed. Your doctor might need to ask yourstate health department to investigate.

Families can reduce their exposure to cyanide bynot breathing in tobacco smoke, which is the mostcommon source of cyanide exposure for the generalpopulation. In the event of a building fire, familiesshould evacuate the building immediately, becausesmoke from burning plastics contains cyanide (andcarbon monoxide). Breathing this smoke can leadto unconsciousness or death. Cyanide in smoke canarise from the combustion of certain plastics (e.g.,polyacryl-amines, polyacrylics, polyurethane, etc.).

Compounds that release cyanide are naturallypresent in plants. The amounts are usually low inthe edible portion but are higher in cassava. Pitsand seeds of common fruits, such as apricots,apples, and peaches, may have substantial amountsof cyanide-releasing chemicals, so people shouldavoid eating these pits and seeds to preventaccidental cyanide poisoning. Parents should teachtheir children not eat fruit pits and seeds. Peopleshould be aware that taking high levels of vitamin Cmay increase the danger of cyanide poisoning fromfruit pits, because more cyanide is released from thepits.

Studies have shown that the effects of cyanide areworse in humans and animals with poor nutrition.Diets containing adequate amounts of proteinshould improve recovery from cyanide exposureincidents.

Is there a medical test to determine whether I have been exposed to cyanide?

Blood and urine levels of cyanide and thiocyanatecan be measured, and small amounts of thesecompounds are always detectable in blood and urinebecause of natural processes. After cyanidepoisoning, increased blood levels of cyanide andthiocyanate are detectable. Harmful effects canoccur when blood levels of cyanide are higher than0.05 parts per million (ppm), but some effects canoccur at lower levels. Tissue levels of cyanide canbe measured if cyanide poisoning is suspected.However, cyanide and thiocyanate are clearedrapidly from the body in urine or exhaled breath; forthat reason, blood measurements are only useful fordetecting recent exposure. A bitter, almond-likeodor in the breath may alert a physician that aperson was exposed to cyanide, but this is notalways found. In general, if cyanide exposure issuspected, treatment should be started immediatelywithout waiting for the results of blood cyanidemeasurements.

What recommendations has the federal government made to protect human health?

The federal government develops regulations andrecommendations to protect public health.Regulations can be enforced by law. The EPA, theOccupational Safety and Health Administration(OSHA), and the Food and Drug Administration(FDA) are some federal agencies that developregulations for toxic substances. Recommendationsprovide valuable guidelines to protect public health,but cannot be enforced by law. The Agency forToxic Substances and Disease Registry (ATSDR)and the National Institute for Occupational Safetyand Health (NIOSH) are two federal organizationsthat develop recommendations for toxic substances.

Regulations and recommendations can be expressedas "not-to-exceed" levels, that is, levels of a toxicsubstance in air, water, soil, or food that do notexceed a critical value that is usually based onlevels that affect animals; they are then adjusted tolevels that will help protect humans. Sometimesthese not-to-exceed levels differ among federalorganizations because they used different exposuretimes (an 8-hour workday or a 24-hour day),different animal studies, or other factors.

Recommendations and regulations are also updatedperiodically as more information becomes available.For the most current information, check with thefederal agency or organization that provides it.Some regulations and recommendations for cyanideinclude the following:

EPA sets regulations for the amount of cyanideallowed in drinking water. The highest amount allowed is 200 micrograms of cyanide per liter ofwater (μg/L or 0.2 ppm). EPA also sets limits foramounts of hydrogen cyanide in stored foods thathave been treated with cyanide to control pests.The maximum amount allowed on citrus fruits is50 ppm. EPA also requires industries to reportspills of 1 pound or more of potassium silvercyanide and 10 pounds or more of hydrogencyanide, potassium cyanide, sodium cyanide,calcium cyanide, or copper cyanide.

OSHA sets levels of cyanide that are allowable inworkplace air. The permissible exposure limit forhydrogen cyanide (HCN) and most cyanide salts is10 ppm or 11 milligrams of cyanide per cubic meterof air (mg/m³) averaged over an 8-hour workdayand 40-hour workweek. NIOSH sets guidelines(recommended exposure limits or RELs) forchemicals in workplace air. The short-term RELfor hydrogen cyanide is 4.7 ppm or 5 mg/m³,averaged over 15 minutes and not to be exceeded atany time in the workday. There is a 10-minuteceiling limit for most cyanide salts of 4.7 ppm or5 mg/m³. NIOSH also determines levels that areimmediately dangerous to life and health (IDLH) ifa worker is exposed for more than half an hour.IDLH levels are 50 ppm for hydrogen cyanide or25 mg/m³ as cyanide for most cyanide salts.

References

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.