Potassium Iodide

Resources

Potassium iodide (chemical formula KI) is a salt that is similar in structure and physical character to common table salt (sodium chloride; NaCl). Indeed, potassium iodide is a common commercial additive to table salt, to produce “iodized” salt.

Potassium iodide is noteworthy in security because of its ability to block the uptake of radioactive iodine by the body’s thyroid gland. Located in the neck, the sole task of the thyroid gland is the production of a hormone that is one of the body’s principle metabolic regulators. Thus, the disruption of the thyroid gland— such as occurs when the uptake of radioactive iodine triggers the development of thyroid cancer—threatens health and can even led to death.

If taken in time following an accidental or deliberate release of radioactive iodine, such as would occur with a leak from a nuclear power plant or the detonation of a bomb containing a radioactive payload, potassium iodide saturates the thyroid with a form of iodine that persists in the gland. The radioactive form of iodine cannot out compete this stable form of iodine, and so is excreted from the body.

Ingestion of KI has long been a precaution for workers in nuclear power plants and for military personnel engaged in a conflict where the use of nuclear weapons is considered to be a possibility. Much of what is known of the protective effects of potassium iodide has come from the measurements of radiation accumulation in the thyroid glands of hundreds of thousands of people in the weeks following the Chernobyl reactor disaster of April 1986, and the therapeutic effects of KI achieved in Poland during that time.

Since the terrorist attacks on the United States in the latter months of 2001, the need for a distribution of KI to civilians has become recognized. This has become especially evident with the exposed vulnerability of nuclear power plants to terrorist attack, and to the conceivable use of “dirty” bombs by terrorists. The latter, essentially a conventional explosive charge that spews out radioactive substances including iodine, could contaminate many people in a crowded urban area.

The protective effects of potassium iodide last about 24 hours from the time it is ingested. Thus, a civilian or military protective strategy requires daily doses of KI. Longer term or more permanent use of the salt is not recommended yet, as prolonged use has been linked to thyroid malfunction, especially in those with Grave’s disease or autoimmune inflammation of the thyroid gland.

See also Decontamination methods; Radioactive decay.

Resources

PERIODICALS

Astakhova, L.N., L.R. Anspaugh, G.W. Beebe, et al. “Chernobyl-Related Thyroid Cancer in Children in Belarus.” Radiation Research no. 150 (1998): 349–356

Robbins, J., and A.B. Schneider. “Thyroid Cancer following Exposure to Radioactive Iodine.” Reviews in Endocrine and Metabolic Disorders no. 1 (2000): 197–203

OTHER

U.S. Food and Drug Administration. “Guidance: Potassium Iodide as a Thyroid Blocking Agent in radiation Emergencies.” Center for Drug Evaluation and Research. December 10, 2001. <http://www.fda.gov/cder/guidance/4825fnl.htm> (accessed October 24, 2006)

Potassium Iodide

OVERVIEW

Potassium iodide (poe-TAS-ee-yum EYE-oh-dide) is a white crystalline, granular, or powdered solid with a strong, bitter, salty taste. It is used as a feed additive, a dietary supplement, in photographic films, and in chemical research.

KEY FACTS

FORMULA:

KI

ELEMENTS:

Potassium, iodine

COMPOUND TYPE:

Binary salt (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

166.00 g/mol

MELTING POINT:

681°C (1260°F)

BOILING POINT:

1323°C (2413°F)

SOLUBILITY:

Soluble in water, ethyl alcohol, acetone, and glycerol

HOW IT IS MADE

A number of methods are available for the preparation of potassium iodide. In one procedure, elemental iodine (I₂) is added to a solution of potassium hydroxide (KOH): I₂ + 6KOH → 5KI + KIO₃ + 3H₂O. The potassium iodide formed is separated from the potassium iodate (KIO₃) by fractional crystallization. That is, the solution is warmed and then cooled. As the temperature falls, the two compounds, potassium iodide and potassium iodate, crystalize out at different temperatures and can be separated from each other. The potassium iodate can then be heated, causing it to decompose and make additional potassium iodide: 2KIO₃ → 2KI + 3O₂.

Potassium iodide can also be produced by reacting hydriodic acid (HI) with potassium bicarbonate: HI + KHCO₃ → KI + CO₂ + H₂O.

Finally, the compound can be made by reacting iron (III) iodide with potassium carbonate (K₂CO₃): Fe₃I₈ + 4K₂CO₃ → 8KI + 4CO₂ + Fe₃O₄.

COMMON USES AND POTENTIAL HAZARDS

Potassium iodide is added to animal feeds to ensure that domestic animals get the iodine they need in their daily diets. A mixture of iodine in aqueous potassium iodide called SSKI has long been used as a disinfectant. The active agent in this mixture is iodine, and the potassium iodide is added to increase the iodine's solubility in water. SSKI is used to purify small amounts of water, to clear up pimples, to prevent sinus infections, and to treat bladder, lung, and stomach infections.

Perhaps the best known use of potassium iodide today is as a treatment for radiation exposure. When a nuclear bomb explodes or a nuclear accident occurs, one of the most dangerous products released to the environment is a radioactive isotope known as iodine-131. Iodine-131 enters the human body and travels to the thyroid, where it attacks cells and tissues, eventually resulting in thyroid cancer. Experts recommend that people exposed to radiation take potassium iodide as a protection against this hazard. The potassium iodide saturates the thyroid gland, making it difficult for the gland to absorb radioactive iodine that may enter the body.

Potassium iodide is also used in the production of photographic film and in a number of chemical tests, such as the determination of dissolved oxygen in water and the presence of starch in an unknown mixture.

Interesting Facts

• Iodized salt contains a small amount of potassium iodide. The potassium iodide is added to ensure that people get enough iodine in their daily diet. A deficiency of iodine results in a medical condition known as goiter, a large swelling in the neck. Before iodized salt was available, many people failed to get enough iodine in their diets and goiter was a very common health problem.
• Potassium iodide occurs naturally in seaweed.

Words to Know

RADIOACTIVE ISOTOPE

A form of an element that gives off some form of radiation and changes into another element.

Under most circumstances, there are no health hazards associated with potassium iodide. Taking an excess of the compound may have harmful effects on the thyroid gland, however. For that reason, people with an overactive thyroid should not take potassium iodide unless so directed by their doctors. Also, a person should not take potassium iodide as a preventative treatment against radiation. It provides no protection in advance of radiation exposure and, in excessive amounts, can create problems of its own for the thyroid.

FOR FURTHER INFORMATION

"Frequently Asked Questions on Potassium Iodide (KI)." U.S. Food and Drug Administration. http://www.fda.gov/cder/drugprepare/KI_Q&A.htm (accessed on November 1, 2005).

"Potassium Iodide." J. T. Baker. http://www.jtbaker.com/msds/englishhtml/p5906.htm (accessed on November 1, 2005).

"Potassium Iodide (Systemic)." Medline Plus. http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202472.html (accessed on November 1, 2005).

Wright, Jonathan V. "One Mineral Can Help a Myriad of Conditions from Atherosclerosis to 'COPD' to Zits." Tahoma Clinic. http://www.tahoma-clinic.com/iodide.shtml (accessed on November 1, 2005).

See AlsoSilver Iodide

Potassium Iodide

Potassium iodide (chemical formula KI) is a salt that is similar in structure and physical character to common table salt (sodium chloride; NaCl). Indeed, potassium iodide is a common commercial additive to table salt, to produce "iodized" salt.

Potassium iodide is noteworthy in security because of its ability to block the uptake of radioactive iodine by the body's thyroid gland. Located in the neck, the sole task of the thyroid gland is the production of a hormone that is one of the body's principle metabolic regulators. Thus, the disruption of the thyroid gland—such as occurs when the uptake of radioactive iodine triggers the development of thyroid cancer—threatens health and can even led to death.

If taken in time following an accidental or deliberate release of radioactive iodine, such as would occur with a leak from a nuclear power plant or the detonation of a bomb containing a radioactive payload, potassium iodide saturates the thyroid with a form of iodine that persists in the gland. The radioactive form of iodine cannot out-compete this stable form of iodine, and so is excreted from the body.

Ingestion of KI has long been a precaution for workers in nuclear power plants and for military personnel engaged in a conflict where the use of nuclear weapons is considered to be a possibility. Much of what is known of the protective effects of potassium iodide has come from the measurements of radiation accumulation in the thyroid glands of hundreds of thousands of people in the weeks following the Chernobyl reactor disaster of April 1986, and the therapeutic effects KI achieved in Poland during that time.

Since the terrorist attacks on the United States in the latter months of 2001, the need for a distribution of KI to civilians has become recognized. This has become especially evident with the exposed vulnerability of nuclear power plants to terrorist attack, and to the conceivable use of "dirty" bombs by terrorists. The latter, essentially a conventional explosive charge that spews out radioactive substances including iodine, could contaminate many people in a crowded urban area.

The protective effects of potassium iodide last about 24 hours from the time it is ingested. Thus, a civilian or military protective strategy requires daily doses of KI. Longer term or more permanent use of the salt is not recommended yet, as prolonged use has been linked to thyroid malfunction, especially in those with Grave's disease or autoimmune inflammation of the thyroid gland.

█ FURTHER READING:

BOOKS:

Harrison, J. R., W. Paile, and K. Baverstock. "Public Health Implications of Iodine Prophylaxis in Radiological Emergencies" in: Thomas, G., A. Karaoglou, and E. D. Williams, eds. Radiation and Thyroid Cancer. Singapore: World Scientific, 1999.

PERIODICALS:

Astakhova, L. N., L. R. Anspaugh, G. W. Beebe, et al. "Chernobyl-Related Thyroid Cancer in Children in Belarus." Radiation Research no. 150 (1998): 349–356.

Robbins, J., and A. B. Schneider. "Thyroid Cancer following Exposure to Radioactive Iodine." Reviews in Endocrine and Metabolic Disorders no. 1 (2000): 197–203.

ELECTRONIC:

U.S. Food and Drug Administration. "Guidance: Potassium Iodide as a Thyroid Blocking Agent in radiation Emergencies." Center for Drug Evaluation and Research. December 10, 2001. <http://www.fda.gov/cder/guidance/4825fnl.htm> (April 9, 2003).

U.S. Nuclear Regulatory Commission. "Frequently Asked Questions About Potassium Iodide." National Research Council. April 2, 2003. <http://www.nrc.gov/what-wedo/regulatory/emer-resp/emer-prep/ki-faq.html> (April 12, 2003).

SEE ALSO

Atmospheric Release Advisory Capability (ARAC)
Chernobyl Nuclear Power Plant Accident, Detection and Monitoring
Nuclear Weapons

iodized salt Usually 1 part of iodate in 25,000–50,000 parts of salt, as a means of ensuring adequate iodine intake in regions where deficiency is a problem.