**2. Iodine species in nature**

Iodine plays an integral role in a diverse array of processes. As such, it exists in a variety of forms reflecting either the environment in which it is found or its biological function. Water,

A Review of Spectrophotometric and Chromatographic Methods

**2.4 Food and plants** 

and inorganic components (Sheppard et al., 1995; Whitehead, 1984).

and Sample Preparation Procedures for Determination of Iodine in Miscellaneous Matrices 373

mg/kg (Muramatsu, 2004). Retention of iodine in the soil is influenced by a number of factors, including the soil pH, moisture content, porosity and composition of the organic

Geographic differences in topsoil iodine content and irrigation procedures determine food iodine levels. In most diets the mainstay sources of iodine are fish, shellfish, milk and iodinated salt. Food supplements constitute an alternative means of obtaining dietary iodine. Fish contain iodine in similar forms to those found in humans. Perhaps the widest assortment of forms is encountered in different species of seaweed. Brown seaweeds contain mostly I-, however green seaweeds play host to a wide array of organic molecules to which iodine is bound, including numerous proteins and polyphenols. Dietary iodine is obtained from a variety of sources and individual dietary habits contribute to the wide disparity in iodine intake among populations. In 1993, the World Health Organization [WHO] published the first version of the WHO Global Database on Iodine Deficiency with global estimates on the prevalence of iodine deficiency based on total goitre prevalence (TGP), using data from 121 countries. Since the international community and the authorities in most countries where IDD was identified as a public health problem have taken measures to control iodine deficiency, in particular through salt iodization programmes – the WHO recommended strategy to prevent and control IDD (World Health Organization [WHO], 2004). Salt iodization programmes are carried out in more than seventy countries, including the United States of America and Canada. There is a wide variation in the scope of iodine supplement; almost 90% of households in North and South America utilize iodized salt while in Europe and the East Mediterranean regions this figure is less than 50%, with a worldwide figure about 70% (WHO, 2007). WHO, ICCIDD (International Council for the Control of Iodine Deficiency Disorders) and UNICEF (United Nations International Children's Emergency Fund) recommend that the term "iodized" be used to designate the addition of iodine to any substance, regardless of the form. Iodine is commonly added as the I- or IO3- of potassium, calcium or sodium. 70% of salt sold for household use in the U.S.A. is iodized with 100 ppm KI (400 µg iodine per teaspoon) (U.S. Salt Institute, 2007). In Canada all salt must be iodized with 77 ppm KI. Mexico requires 20 ppm levels of iodization. Recommendations for the maximum and minimum levels of iodization of salt are calculated as iodine and determined by local national health authorities in accordance with regional variations in iodine deficiency. In Poland iodine deficiency prophylaxis was first started in 1935. Near the end of the 1940's and 80's, the practice of iodizing table salt was abandoned. A nonobligatory recommendation of iodizing salt took place in 1989. In 1991 the Polish Council for Control of Iodine Deficiency Disorders (PCCIDD) was established and an epidemiological survey performed in 1992-1993, defined Poland as an area with moderated – the seaside region as light – severity of iodine deficiency. In 1996 the production of table salt without the addition of KI was made illegal. An obligatory law was passed, mandating the addition of 30(+/-10) mg of KI per kilogram of salt (Szybiński, 2009). Iodization of salt in Turkey has been mandatory since 1998 and the recommended iodine concentration is 50-70 mg KI/kg or 25- 40 mg KIO3/kg (Gurkan et al., 2004). In Switzerland, iodization of salt was altered three times. Iodization was first introduced in 1922 at 3.75 mg/kg. In 1962 the concentration was doubled and in 1980 it was doubled again giving a present level of 15 mg/kg. Although it's use is voluntary, by 1988, 92% of retail salt and 76% of all salt for human consumption

air, soil and food constitute the most common group of analyzed samples derived from our external environment.

#### **2.1 Water**

In water iodine is predominantly found in the iodide (I-) or iodate (IO3 -) form (Gilfedder et al., 2007; Schwehr & Santschi, 2003). Other forms of iodine species in water include: IO4- (periodate), IO- (hypoiodite), CH3I (methyl iodide), CH2I2 (methyl diiodide), C2H5I (ethyl iodide), C3H7I (propyl iodide), C 4H9I (butyl iodide), and CH2 BrI (methyl iodide bromide) (Hou, 1999, Hou et al., 2009). Organic iodine concentrations may be especially high in fresh water (from rivers, lakes and rain).

#### **2.2 Air**

Generally, the air contains iodine in particulate form, as inorganic gaseous iodine (I2, HIO) and as some forms of organic gaseous iodine (CH3l, CH2l2). High iodine concentrations are found in urban areas due to the combustion of oil and coal. Coastal areas also have high iodine concentration due to the emission of gaseous I2 from algae, seawater and sea spray, which varies with location, season and climate (Hou, 2009; Yoshida & Muramatsu, 1995). There are numerous pathways that may be responsible for transferring I2 from the sea to air. Photochemical oxidation of I from seawater to elemental iodine has been recreated in the laboratory (Miyake & Tsunogai, 1963). Another means of obtaining elemental I2 is through the reaction of I with ozone (O3)(Garland & Curtis, 1981). The greatest source of atmospheric I2 is thought to be from microbial activity within the oceans, through the transformation of I and IO3 into organic CH3I, which has a residence time between 1.1-8 days (Cicerone, 1981). Lovelock et al. (Lovelock et al., 1973) measured the mean atmospheric CH3I concentration above the Atlantic as 1.2 ppt (6.8 ng/m3). Rasmussen et al. (Rasmussen et al., 1982) found the background level of CH3I to vary between 1 and 3 ppt (5.7-17 ng/m3) with measurements near oceans with high biomass productivity to be around 7-22 ppt (40-125 ng/m3).

#### **2.3 Soil**

Strong evidence suggests that atmospheric transport from the oceans is responsible for the deposition of iodine in soil. Iodine exists in various forms in soil and varies largely with respect to its concentration. I- (more mobile form) is believed to be the dominant species in acidic soils whilst IO3- (less mobile) will occur in alkaline soils. In low pH oxidizers, e.g. Fe3+ and Mn4+ convert I - into molecular I2. The activity of reducing bacteria impacts the form of iodine in the soil as well. CH2I2 and other volatile organic complexes of iodine are generated by microbial activity (Johnson, C.C. 2003). Generally, organic bound iodine is more abundant in soil samples. The secondary environment (soil) has high iodine content compared to the primary environment (parent rocks) from which it is derived as a result of weathering. Weathered rocks and soils are richer in iodine than the unweathered bedrocks (Fuge & Johnson, 1986). On average, the igneous rocks contain an average of 0.25 mg/kg of iodine, the sedimentary rocks have 2.3 mg /kg iodine and the metamorphic rocks have 0.81 mg/kg of iodine. Organic matter is the major concentrator of iodine in sedimentary basins (Mani et al., 2007). The highest values were found in soil samples from areas close to the coast, where there is high rainfall, and from areas with high soil organic matter. In one study, the iodine concentration in Japanese soils was found to range from 0.2 mg/kg to 150 mg/kg (Muramatsu, 2004). Retention of iodine in the soil is influenced by a number of factors, including the soil pH, moisture content, porosity and composition of the organic and inorganic components (Sheppard et al., 1995; Whitehead, 1984).
