Iodine concentration ocean

Although iodine in oceans is only 0.8% of the total iodine on the earths crust (Muramatsu and Wedepohl, 1998), it enters the human food chain via three important processes (1) the evaporation of iodine from seawater into the air, its subsequent deposition onto soils and in fresh water, and final incorporation into terrestrial plants and animals (2) a higher incorporation into microorganisms, seaweeds, and fish, which are used as food and nutritional supplements and (3) extraction of iodine from pore water that contains no sediments and higher concentrations of iodine and using it for various purposes, e.g., as an additive to edible salt. 

Total dissolved iodine concentration is almost constant at 0.4—0.5 xM in most stations thus, the ocean is a huge reservoir of iodine. 

There are only two isotopes of iodine present in nature, and 1291. I27p as the only stable isotope of iodine, is widely distributed in the environment. The reported iodine concentration on the earth is normally quite low, 0.25 ppm in the earths crust (Muramatsu and Wedepohl, 1998), lOng/ m3 in the atmosphere and 0.05 ppm in the biosphere on the basis of fresh mass (Shinonaga et ai, 2001). The main reservoir of iodine in the earth s crust is the ocean and sea, approximately 70% of the iodine in the earth s crust is bound to ocean sediments (Muramatsu and Wedepohl, 1998). The iodine concentration in seawater (40-60ng/ ml) is much higher than in freshwater ([Pg.437]

Iodine concentration in the atmosphere generally diminishes with increasing distance from the oceans. This reduction consequently reduces the amount of iodine transferred to inland soils by precipitation scavenging and dry deposition. The period of exposure of the soil to these processes also affects the iodine deposit. Hence, the concentration of iodine is generally lower in young postglacial soils, particularly in their deeper horizons (Goldschmidt, 1954). 

Fish, poultry, and meat can be major sources of dietary iodine. Iodine in fish reflects its content in the water they inhabit. One study showed that ocean fish have a mean iodine concentration of 832 pg/kg, in contrast to 30 pg/kg in fresh water fish (8). Koutras (4) reported 64 pg iodine in a normal portion of fish in Athens. It is generally assumed, probably correctly, that much of the iodine sufficiency of coast dwellers is from the consumption of marine fish. In addition to direct consumption, iodine from marine fish can find its way into the human diet via its use in fertilizers and animal feeds. 

Similar elements also occur in the same natural environment. For instance, the halogens are markedly concentrated in seawater. (The major salt in ocean brines is sodium chloride.) The other halogens are extracted from seawater that has been further concentrated—bromine from salt beds formed by evaporation and iodine from kelp, which grows in oceans. 

Fluorine exists as F and MgF+ in seawater in approximately equal concentrations. The free ion fractions of Cl and Br- are essentially 100%. Iv in the form IO3 is the thermodynamically favoured (stable) form of iodine in oxygenated seawater. In the upper ocean, where thermodynamic disequilibria are common, a significant fraction of total iodine is present as iodide (I-). IO3, like I , is weakly interactive. 

High EF values were also noted for Cu (<90-400), Zn (<120-830), and Mn (1-500), with the lower ranges reported for the rural airport site. Iron showed relatively low EF values (< 1 to 30). Vanadium exhibited EF values generally from 1 to 10 with the exception of one event where the value was 68. Concentrations from chromium never exceeded 30 ppb with EF values ranging from 25 to 100. Halogen EF values, when compared to sodium concentrations in the ocean, were generally less than 10 with the exception of iodine. The iodine enrichment is believed not to be anthropogenic but to arise From preferential enrichment from the oceans (7). 

Iodine tends to be concentrated in Earth s crust in only a few places. These places were once covered by oceans. Over millions of years, the oceans evaporated. They left behind the chemical compounds that had been dissolved in them. The dry chemicals left behind were later buried by earth movements. Today, they exist underground as salt mines. 

Table 7.1. Concentration of bromomethanes and iodinated alkanes in the surface sea water of the open Southern Ocean compared with a coastal site on Spitsbergen (5, 20. 23, 40)...

Concentration of bromomethanes and iodinated hydrocarbons in surface sea water of the Southern Ocean... 

Bromomethanes at single locations in the South Atlantic normally show lower concentrations than or similar to those measured for the Southern Ocean. For example, Class and Ballschmiter determined the bromoform and dibromomethane concentration at 6° S, 6° W to be 0.8 and 0.3 ng F (3), whereas Abrahamson and Klick measured higher contents of 4.5 and 1.3 ng l at 52° S, 6°W (55), respectively. The latter authors also reported low concentrations of iodochloromethane and iodopropane in the range of 0.07-0.13 ng 1 in an Antarctic sea water sample. That diiodomethane is the dominant iodinated compound in coastal waters, especially during spring, was found by Klick on the Swedish coast (56). This confirms the results listed in Table 7.1 for Arctic coastal water. 

The mean concentrations of bromomethanes of this north-south profile are lower by a factor of 1.5-3.6 compared with the concentrations listed in Table 7.1 for the Southern Ocean. On the other hand, the mean values for iodomethane are nearly identical with 0.4 ng 1 for the north-south profile of Figure 7.9 and 0.3 ng r for the Southern Ocean, respectively. More investigations must be carried out to better identify the real parameters which result in differences in the production of brominated and iodinated hydrocarbons in the polar regions compared with the other oceans. 

Diiodomethane was the most abundant iodinated hydrocarbon in all meltwater ponds, which was also observed in coastal waters of the Arctic Ocean (Table 7.1). lodomethane and iodochloromethane were determined in a comparable concentration, where in three of seven ponds the CH2ICI concentration exceeded that of CH3I. This again demonstrates that iodomethane is not the only species to play an important role in the biogeochemical cycle of I in polar regions. 

Riley, 1975). The 11 ions, except for iodine, compose more than 99.9% of salinity. Iodine is one of the most abundant micronutrients in seawater, with a total concentration of 5 X 10 to 6 X 10 g-l (0.4-0.5pM). Other micronutrients, such as nitrogen and phosphorus and many trace ions, are also contained therein. The three main oceans (i.e., the Atlantic, Indian, and Pacific oceans), including adjacent seas, occupy 70.8% of the earths surface (total sea area of 360.8 X 10 km ). Of the sea area, the ratio of the continental shelf (less than 200m deep), between 200 and 2000 m deep, and over 2000 m deep is 7.6, 8.5, and the remaining 83.9%, respectively. The total volume of seawater is 1.37 X 10 m (mean depth 3795 m) (Bowden, 1975). The ocean is thus a huge reservoir of iodine. 

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