Where Found (Encyclopedia of Global Resources)
Iodine is widely distributed at a low concentration. However, only in brines and caliche ores is the concentration sufficient to make separation practical. The largest producers of iodine are Chile, followed by Japan, China, Turkmenistan, Russia, Azerbaijan, Indonesia, and Uzbekistan.
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Primary Uses (Encyclopedia of Global Resources)
Technical Definition (Encyclopedia of Global Resources)
Iodine (abbreviated I), atomic number 53, belongs to Group VII (the halogens) of the periodic table of the elements and resembles chlorine in its chemical properties. One stable isotope exists with an atomic weight of 126.9045. At room temperature, iodine is a purple-black color with a metallic sheen. Its elemental form is diatomic (two atoms of iodine bonded together). The solid has a density of 4.942 grams per cubic centimeter and sublimes easily. The melting point of iodine is 113.7° Celsius, and the boiling point is 184.5° Celsius.
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Description, Distribution, and Forms (Encyclopedia of Global Resources)
Iodine is the sixtieth element in order of abundance, at 0.46 part per million in the Earth’s crust. Commercial deposits are usually iodates such as lautarite Ca(IO3)2 and dietzeite 7Ca(IO3)2·8CaCrO4. Some brines in Louisiana, California, and Michigan contain 30 to 40 parts per million iodide ion, while some Japanese brines contain 100 parts per million. Iodine is only 0.05 part per million in seawater, but some sea plants concentrate iodine up to 0.45 percent (4,500 parts per million) of their dry weight.
Iodine is a necessary trace element in animals. An iodine deficiency may cause a range of problems, including goiter, mental retardation, increased stillbirths and miscarriages, and the severe mental and physical handicaps of cretinism. Common table salt (“iodized” salt) contains iodine at a 0.01 percent level, which is enough to safely prevent these ailments. Iodine is used in the body to produce the growth-regulating hormone thyroxine. An excess of iodine may lead to thyroid cancer or interfere with hormone production. Although throughout history, iodine shortage has normally been the problem, the use of iodine in animal feed, sanitizers, and food processing causes Americans to consume many times the recommended daily allowance of iodine. The effects of this are not truly known, but it may prove to be unhealthy. Iodine is highly toxic to plants and does not appear to be...
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History (Encyclopedia of Global Resources)
In 1811, Bernard Courtois, the son of a saltpeter manufacturer, first noticed iodine while extracting compounds from the ash of algae gathered along the seashore. He observed a cloud of violet vapor and an irritating odor. Courtois tested the dark crystals that formed on cold objects as well as he could in his simple laboratory. Because he suspected that this was a new element, he provided samples to two of his friends, Charles-Bernard Desormes and Nicolas Clément at the Conservatoire des Arts et des Métiers. With better equipment, they continued the investigation of this new substance and announced the discovery of iodine in 1813. The name comes from the Greek word iodes, for “violetlike.” The first iodine-containing mineral was found in Mexico in 1825. The discovery of iodate as a contaminant of the Chile saltpeter beds was an even more important discovery.
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Obtaining Iodine (Encyclopedia of Global Resources)
The method of iodine production depends on the source of the iodine. From the Chilean saltpeter beds, the sodium iodate is dissolved by an alkaline solution, converted to iodide ion by reaction with sodium hydrogen sulfite, and iodine is then precipitated by adding iodate solution. From brines, the iodide ion is converted to iodine by reaction with chlorine. Air blowing through the solution collects the iodine, which then precipitates. Purification is by resublimation. In an alternate method the iodide ion is precipitated with silver ion, reacted with iron to make iron iodide, and reacted with chlorine to produce iodine. Another method uses an ion-exchange resin to collect the iodine after it has reacted with chlorine. The annual production of iodine is about 25,000 metric tons.
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Uses of Iodine (Encyclopedia of Global Resources)
Iodine has a multitude of small-percentage usages. It is difficult to track percentages of iodine devoted to specific consumer end uses, because many intermediate iodine compounds—such as ethyl and methyl iodide, crude iodine, potassium iodide, sodium iodide, povidine-iodine, and ethylenediamine dihydroiodide—are marketed to manufacturers before end-use patterns can be established.
Iodine is used in catalysts for synthetic rubber manufacture, stabilizers, dyestuffs, pigments, sanitizers, pharmaceuticals, lithium-iodine batteries, high-purity metals, motor fuels, lubricants, and photographic chemicals for high-speed negatives (a declining use with the advent of digital cameras and other digital-imaging systems). An alcohol solution of iodine called tincture of iodine is a well-known antiseptic. A possible use may be in trifluoromethyl iodide (CF3I) as a replacement for chlorofluorocarbons (CFCs) as refrigerants. The trifluoromethyl iodide does not cause the damage to the ozone layer that the CFCs do.
Radioactive iodine, either I-123 or I-131, can be used to treat thyroid disease, including cancer, or as a contrast agent in generating medical images, particularly of the thyroid. Iodine can also be used as a contrast agent in producing X rays of soft tissue such as the gallbladder. Uses of iodine will continue to develop, as it is a reactive element that forms compounds with every group of elements except the noble...
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Further Reading (Encyclopedia of Global Resources)
Fernandez, Renate Lellep. A Simple Matter of Salt: An Ethnography of Nutritional Deficiency in Spain. Berkeley: University of California Press, 1990.
Greenwood, N. N., and A. Earnshaw. “The Halogens: Fluorine, Chlorine, Bromine, Iodine, and Astatine.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Hetzel, Basil S. The Story of Iodine Deficiency: An International Challenge in Nutrition. New York: Oxford University Press, 1989.
Kogel, Jessica Elzea, et al., eds. “Iodine.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration, 2006.
Massey, A. G. “Group 17: The Halogens: Fluorine, Chlorine, Bromine, Iodine, and Astatine.” In Main Group Chemistry. 2d ed. New York: Wiley, 2000.
Mertz, Walter, ed. Trace Elements in Human and Animal Nutrition. 5th ed. 2 vols. Orlando, Fla.: Academic Press, 1986-1987.
U.S. Geological Survey. Iodine: Statistics and Information. http://minerals.usgs.gov/minerals/pubs/commodity/iodine
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Iodine (Chemical Elements)
Iodine is the heaviest of the commonly occurring halogens. The halogens are in Group 17 (VIIA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Iodine's chemical properties are similar to the lighter halogens above it, fluorine, chlorine, and bromine. But its physical appearance is very different. It is a steel-gray solid that changes into beautiful purple vapors when heated.
Iodine was discovered in 1811 by French chemist Bernard Courtois (1777-1838). The element occurs primarily in seawater and in solids formed when seawater evaporates. Its single most important property may be the ability to kill germs. It is used in antiseptics, germicides (products that kill germs), and other medical applications. However, it has a great many other less common, but important, commercial applications.
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Iodine (Encyclopedia of Alternative Medicine)
Iodine is a trace mineral required for human life. Humans require iodine for proper physical and mental development. It impacts cell respiration, metabolism of energy and nutrients, functioning of nerves and muscles, differentiation of the fetus, growth and repair of tissues, and the condition of skin, hair, teeth, and nails. Iodine is also needed for the production of thyroid hormones. The thyroid (a small gland in the front of the neck), which contains 80% of the body's iodine pool, converts iodine into the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones are released into the bloodstream, controlling the body's metabolism.
As established by the National Research Council's Food and Nutrition Board, the revised 1989 Recommended Dietary Allowance (RDA) for iodine is 40 mcg for infants, increasing to 150 mcg for adults and children age 11 and older. The RDA for pregnant and lactating women increases to 175 and 200 mcg respectively. Harrison's Principles of Internal Medicine reports that average U.S. iodine daily intake ranges from approximately 0.5.0 mg. According to the Merck Manual of Diagnosis and Therapy, less than 20 mcg per day of iodide results in iodine deficiency; iodide intake 20 times greater than the daily requirement (2 mg) results in...
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Iodine (Encyclopedia of Public Health)
Iodine is a critically important component of thyroid hormones. There are four iodine atoms per molecule of l-thyroxine, and three per molecule of l-triiodothyronine. The highest content of iodine in food is found in fish, with lesser amounts occurring in eggs, milk, and meat. Fruits and vegetables contain little iodine. Without iodine supplementation, people in most inland areas of the world, particularly mountainous regions, have iodine deficiency. This was the case in the United States before iodinization of salt. When iodine deficiency prevails, goiter and hypothyroidism commonly occur, along with congenital cretinismll preventable diseases. Iodine excess, usually a result of diagnostic medical procedures or medications, can produce either hypothyroidism or hyperthyroidism in patients with different types of underlying thyroid disease.
MARTIN I. SURKS
(SEE ALSO: Goiter; Hyperthyroidism; Hypothyroidism; Thyroid Disorders)
Medeiros-Netos, G. (1999). "Congenital and Iodine-Deficiency Goiters." In Atlas of Clinical Endocrinology, Vol. 1: Thyroid Diseases, ed. M. I. Surks. Philadelphia, PA: Current Medicine.
Iodine (Encyclopedia of Food & Culture)
IODINE. Iodine is an essential dietary element necessary for normal development and function of all vertebrates. Its sole physiological function is as a constituent of the thyroid hormones, thyroxine and triiodothyronine. It is removed from the blood by the thyroid gland for storage in organic form where it is found as iodinated amino acids in peptide linkage in thyroglobulin, a highmolecular weight protein.
Iodine is widely but usually sparsely distributed in nature, so that in vast areas of the world the supply in customary diets is marginal or insufficient. It has been estimated that over two billion persons are at risk of disorders attributable to iodine deficiency. Among these disorders are goiter, impaired intellectual function, growth retardation, reduced fecundity, lowered work capacity, increased rates of fetal loss and infant mortality, deafness, and in extreme instances a well-defined but somewhat varied constellation of physical findings collectively known as cretinism. Cretins are recognized by severe mental deficiency, disturbances in gait, impaired or absent hearing, and other neurological defects, but the signs and symptoms in these individuals may be subtle. These features merge with those of the less impaired members of the same community or nearby countryside where they may appear in lesser severity.
The iodine content of edible plants is largely dependent on the iodine content of the soil on which they are grown. The iodine content of foods of animal origin depends on the iodine in their food. Iodine is concentrated in milk, and is found in relatively high concentration in sea fish, who are at the upper levels of the food chain that contains algae. Some sea fish concentrate iodine from sea water. The only structure among the vertebrates that contains a significant amount of iodine is the thyroid gland.
Role of Iodine in Disease
For centuries the disorders arising from iodine deficiency have been recognized in well-defined regions. These have been called "goiter belts." Switzerland was included in the goiter belt until the iodine deficiency in that country was corrected in the first half of the twentieth century. Until recent years iodine deficiency was a recognized disorder in the United States, especially the Midwest and West, where goiter was commonplace. Iodine deficiency has been a major public health problem in the Andean region and eastward, in large areas of central and north Africa, in the Middle Eastern countries, in India, and in eastern and central Europe, and even today in localized regions of western Europe. Fortunately, remarkable headway has been made in elimination of iodine deficiency through various methods of supplementing diets.
Goiter is only one of the many consequences of iodine deficiency, and is relatively trivial when compared with the damaging effects of iodine deficiency on the nervous system. From the human point of view, it is more correct to speak of "endemic mental deficiency" than "endemic goiter."
Endemic thyroid disease has traditionally been considered a feature of iodine deficiency in the mountainous regions of the world. Endemic thyroid disease is found in regions of high elevation, but has also been common where glacial run-offs occur and in floodplains where there has been chronic leaching of the soil. Such geographic regions include the Gangetic plain and much of India and southeastern Asia, the Himalayan region, and central Africa, where the iodine deficiency disorders are frequent and severe; the coastal regions of western Europe are marginally iodine deficient. Endemic iodine deficiency can be detected almost anywhere with currently available sensitive techniques. In the United States until recently the mean intake of iodine was excessive, but recently has been rapidly falling into a normal range. The recent precipitous fall in iodine consumption in the United States has led to concern that iodine deficiency may again become a problem if the present rate of decline continues. The need for monitoring iodine intake is apparent. This is customarily done by measuring the iodine content of urine from a fair sample of the population under observation.
The optimal daily adult iodine intake is about 150 μ g/day, about half that for children and infants. This figure rises to about 200 μ g during pregnancy, but under normal circumstances there is wide latitude in intake because of the ability of the normal thyroid system to compensate for varying levels of supply. The thyroid and pituitary through a feedback relationship provide a highly efficient regulatory system. If iodine intake falls below about 50 μ g/day the pituitary gland becomes stimulated to increase its iodine uptake and hormone production, and, if the iodine supply exceeds needs, the pituitary shuts down appropriately.
Iodine is readily absorbed by the stomach and upper gastrointestinal tract. Iodine in chemical combination is released in the gut and absorbed; it may be rapidly taken up by the thyroid gland or excreted in the urine. Only a small fraction appears in the stool. Exceptions occur when iodine is in chemical combination with such drugs used as radio-contrast agents and amiodarone, the widely used cardiac medication.
Iodine Deficiency and Disease
Certain chemical agents found in some foods interfere with the uptake or utilization of iodine by the thyroid. Among these are the cyanoglycosides found in cassava (manioc), a component of millet, and a variety of chemical agents and some unidentified substances found in the effluent water from rock formations and in factory discharges. It must be stressed that the inhibitory effect of these substances may be bypassed if there is an ample supply of iodine in the diet, but their effect may be critical if the iodine intake is marginal or lower.
When marginal or low iodine intake is identified in a geographic regions such as a district or country, an effort should be made to correct the deficiency. A variety of techniques have been employed. These include distribution of iodine solution to school attendees, candies containing potassium iodide, addition of iodine to drinking water, and the use of canisters containing iodine that is slowly released into sources of drinking water. None of these methods has proved to be widely accepted. In addition, it should be stressed that the primary target for the prevention of neurological damage due to iodine deficiency is the pregnant and nursing mother.
Prevention of Iodine Deficiency
The most effective and widely employed method for correcting iodine deficiency is salt iodization. The technique is simple, inexpensive, and effective. Potassium iodate rather than iodide salts is used because it is more stable when mixed with salt. Nevertheless certain problems must be corrected. Unscrupulous traders may sharply increase the cost of iodized salt to the consumer. If improperly stored the iodine may sublime and be lost from the salt. If addition of iodine by the manufacturer is not done carefully the salt may be overiodinated. In certain cases, especially those in which people have nodular goiters resulting from prolonged iodine deficiency, thyrotoxicosis may result, which may be subtle in onset and chronic, with unwanted or disastrous results. Careful and continued monitoring of dietary supplementation by iodized salt must be done, as with all food additives.
Promotion of salt iodization, especially in areas of particular need in the developing world, has been a health priority of many public and private agencies, including the World Health Organization, UNICEF, the International Council for Prevention of the Iodine Deficiency Disorders, and others. One of the principal problems with programs of salt iodization is that governments tend to lose interest, and the programs lapse, leading to recurrence of the iodine deficiency disorders. Again, constant monitoring is the key to continued success.
Injections of heavily iodinated poppyseed and other oils have been tried in mass campaigns, first in New Guinea; these methods have since been widely employed elsewhere. These are the same oils that have been widely used as radio-contrast agents. The results have been impressive. The iodine is slowly released from the oil and may be effective for two or more years. The oral route has also been used to administer the oils, but effectiveness is less prolonged. The disadvantages of programs using iodinated oil are principally cost and the requirement for sterile needles and trained personnel, which may be difficult to obtain in remote regions. Iodine-induced thyrotoxicosis may occur after administration of iodinated oil.
A unique and successful method of iodine distribution has recently been introduced. This method can be used in regions where iodine can be drip-added to irrigation water. It has been used in the desert regions of western China with salutary human benefit, and with a highly satisfactory effect on livestock production. The problems with this method are the need for skilled personnel to add the iodine to the irrigation system at the right time and rate, and the fact that it is only feasible when it is possible to add iodine to irrigation water. A somewhat similar technique that has proved beneficial is adding iodine to a municipal water supply. As with other methods of iodine supplementation, skilled maintenance of the program is essential, and the subsequent appearance of thyrotoxicosis is unknown.
Iodine is thinly distributed in the earth's crust, and much of the human population lives in regions that have marginal or insufficient iodine. Mountainous regions, flood-plains, and regions where there has been extensive leaching of iodine from the soil may not provide sufficient iodine for human needs. The result is the appearance of iodine deficiency disorders, which include neurological damage, goiter, increased fetal and infant mortality, deafness, and diminished human energy and resulting economic underproductivity. Iodine deficiency is a major public health problem for a large fraction of the world's population.
Wherever marginal or insufficient iodine exists, implementation of iodine supplementation is required. This may be done by supplementing table salt with iodine, administration of iodinated oil by injection or orally, or addition of iodine to the drinking water. It is essential that a monitoring system be in place to ensure that the population is receiving an adequate iodine intake. Care must be exercised to avoid an excess of iodine, which might induce thyrotoxicosis.
See also Body Composition; Fluoride; International Agencies; Malnutrition; Nutrition; Nutrition Transition: Worldwide Diet Change; Salt; Sodium; Trace Elements.
Braverman, L. E., and R. D. Utiger, eds. Thyroid: A Fundamental and Clinical Text. 7th ed. Philadelphia: Lippincott, Williams, & Wilkins, 2000.
De Long, G. R., J. Robbins, and P. G. Condliffe, eds. Iodine and the Brain. New York: Plenum. 1989
De Long, et al. "Effect on infant mortality of iodination of irrigation water in a severely iodine-deficient area of China." Lancet 360 (1997).
Fernandez, R. L. A Simple Matter of Salt. Berkeley: University of California Press, 1990.
Gaitan, F., ed. Environmental Goitrogenesis. Boca Raton, Fla.:CRC Press, 1989.
Hetzel, B. S. The Story of Iodine Deficiency. New York: Oxford University Press, 1989.
Hetzel, B. S., and C. S. Pandav. S.O.S. for a Billion. Bombay: Oxford University Press, 1996.
Stanbury, John B., and John T. Dunn. "Iodine and the Iodine Deficiency Disorders." In Present Knowledge in Nutrition, 8th ed., edited by B. A. Bowman and R. M. Russell, p. 344. Washington, D.C.: ILSI Press, 2000.
Stanbury, J. B., et al. "Iodine-Induced Hyperthyroidism: Occurrence and Epidemiology." Thyroid 8 (1998).
World Health Organization. Assessment of Iodine Deficiency Disorders and Monitoring their Elimination. 2nd ed. World Health Organization, 2001.
John Stanbury John T. Dunn