Seaweed, iodine-containing

Iodine-containing seaweed is widely consumed in Japan, and to a lesser extent in other industrialized countries. The iodine content differs considerably among kelp species. In Hokkaido daily ingestion of over 100 mg iodine as kelp has been reported (11). Iodine in the Japanese diet can vary widely from day to day depending on the inclusion of kelp. 

Iodine Iodine is a volatile purple-black solid with a beautiful metallic sheen. As the least reactive halogen, iodine is safe to handle and is widely used as a skin disinfectant. It was first prepared in 1811 from seaweed ash, but commercially useful deposits of the iodine-containing minerals lautarite (CaIC>3) and dietzeite [7 Ca( 103)2 8 CaCr04] were subsequently found in Chile. Iodine is used in the preparation of numerous organic compounds, including dyes and pharmaceutical agents, but there is no one single use of major importance. 

In euthyroid subjects with normal glands an excess of iodide from any source can cause goitre (with or without hyperthyroidism), e.g. use of iodide-containing cough medicines, iodine-containing radio-contrast media, amiodarone, seaweed eaters. 

These studies reflect the marked heterogeneity that can characterize vegetarian and vegan diets. In two studies, subjects were directed to avoid iodized salt, fish, seaweed and kelp, and iodine-containing processed foods, while only iodine-free beverages were provided (Abdulla et al, 1981 Remer et al., 1999). In these individuals, iodine... 

Kasagi et al. (2003) Observational study Japan Recovery of primary hypothyroidism following restriction of iodine-containing drugs and foods, such as seaweed products, in patients with increased 9S"Tc uptake and elevated nonhormonal iodine levels due to habitual ingestion of seaweed... 

Iodine is an essential component of thyroid hormones, and iodine deficiency can lead to severe hypothyroidism. On the other hand, excessive iodine intake also results in thyroid dysfunction in certain persons. Coindent described the first case of iodine-induced hyperthyroidism in 1821 (Fradkin and Wolff, 1983), and Hurxthal (1945) reported the first case of iodine-induced hypothyroidism. Ingestion of iodine-rich foods, such as seaweed, can cause hyperthyroidism, and the incidence of hyperthyroidism showed an increase in regions of dietary iodine deficiency after prophylactic iodization of bread or salt. Iodine-containing pharmaceuticals, such as povidone-iodine (PVP-I), radiographic contrast media and amiodarone, are a major source of excessive iodine intake (Wolff, 1969 Fradkin and Wolff, 1983 Markou et aL, 2001 Roti and degli Uberti, 2001). 

The synthesis of thyroid hormone is regulated, and in the absence of thyroid disease provision of additional iodine does not increase hormone secretion except in people who were iodine deficient. Nevertheless, there are people who market various iodine-rich preparations to aid weight loss. Foremost among these are the so-called slimming patches, which contain seaweed extract as a source of iodine which is supposed to be absorbed from a small patch applied to the skin. There is no evidence that such patches have any beneficial effect at all. 

Iodine occurs to a minute extent (less than 0.001 %) in sea water, but is found in greater concentration, combined in organic form, in certain seaweeds, in oysters and in cod livers. Crude Chile saltpetre, or caliche contains small amounts of sodium iodate, NalOj. from which iodine can be obtained (see below). Some insoluble iodides, for example liiose of silver and mercury(II), occur in Mexico. Iodine is found in the human body in the compound thyroxin in the thyroid gland deficiency of iodine in diet causes enlargement of this gland (goitre). 

Manufacture and Processing. The industry related to iodine production began a few years after the discovery of the element by Courtois in 1811. The production processes are based on the raw materials containing iodine seaweeds, mineral deposits, and oh-weh or natural gas brines. 

Seaweeds. The eadiest successful manufacture of iodine started in 1817 using certain varieties of seaweeds. The seaweed was dried, burned, and the ash lixiviated to obtain iodine and potassium and sodium salts. The first process used was known as the kelp, or native, process. The name kelp, initially apphed to the ash of the seaweed, has been extended to include the seaweed itself. About 20 t of fresh seaweed was used to produce 5 t of air-dried product containing a mean of 0.38 wt % iodine in the form of iodides of alkah metals. The ash obtained after burning the dried seaweed contains about 1.5 wt % iodine. Chemical separation of the iodine was performed by lixiviation of the burned kelp, followed by soHd-Hquid separation and water evaporation. After separating sodium and potassium chloride, and sodium carbonate, the mother Hquor containing iodine as iodide was treated with sulfuric acid and manganese dioxide to oxidize the iodide to free iodine, which was sublimed and condensed in earthenware pipes (57). 

On a smaller scale, the largest producer of iodine is Japan where it is extracted from. seaweed containing more than 0.05 parts per million. The most important industrial iodine compound is silver iodide used with silver bromide in photography. Iodine is important in medicine for treating thyroid problems by adding it to table salt. It is used directly as a disinfectant, and a component of d vs. Crystalline silver iodide is used for cloud seeding. 

Iodine occurs as iodide ions in brines and as an impurity in Chile saltpeter. It was once obtained from seaweed, which contains high concentrations accumulated from seawater 2000 kg of seaweed produce about 1 kg of iodine. The best modern source is the brine from oil wells the oil itself was produced by the decay of marine organisms that had accumulated the iodine while they were alive. Elemental iodine is produced by oxidation with chlorine ... 

In 1862, E. C. C. Stanford proposed the carbonization of the drift-weed in closed retorts so as to recover tar and ammoniacal liquor in suitable condensers. This modification did not flourish because of the subsequent difficulties in extracting soluble iodides from the charcoal. V. Vincent (1916) claims that soln. containing aluminium sulphate extract the alkali iodides from seaweed leaving behind the organic matter which prevents the direct precipitation of iodine or iodides. The alkali iodide soln. is treated with copper sulphate for cuprous iodide, or by soln. of sulphites for iodine. M. Paraf and J. A. Wanklyn proposed to heat the drift-weed first with alkali hydroxide so as to form oxalic and acetic acids, which could be crystallized from the lixivium. The economical treatment of seaweed for iodine has been discussed by A. Puge. 

Most feedstuffs contain only low levels of iodine. The exception is seaweed, which can contain 4000-6000 mg/kg of iodine. 

---