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Trace Elements in Abiotic and Biotic Environments
common in oceans and brine pools water. Some I species are unstable in water,
and are transferred to iodate in alkali media, and to iodite in acid media. The photochemical, as well as biological oxidation, of iodide ions to iodate ions in surface
water is a significant source of this element in the atmosphere.
The average I content in river water is estimated within the range of 2–15 μg/L
(Table 21.1). However, in some stream water, it may be concentrated up to 198 μg/L
(Reimann and de Caritat 1998). Also, in some lakes (e.g., in central Kazakhstan),
its content can reach up to 160 μg/L (Fuge and Johnson vide Kabata-Pendias 2011).
Relatively high concentration of the isotope 129 I was measured in Swedish rivers,
apparently from some nuclear reprocessing facilities in France and England (Kekli
et al. 2003).
Median I concentration in bottled water of the EU countries is 4.8 μg/L, and in
tap water it is 3.2 μg/L (Birke et al. 2010). Low I concentration in drinking water
may have an impact on cardiovascular disorders. There are still inadequate data to
establish a health guideline value, and lifetime exposure of I through water disinfection (WHO 2011a).
21.4 AIR
Median I concentration of air in remote regions is 1.1  ng/m 3 , within the range of
0.08–4.4 ng/m 3 , whereas in contaminated areas its content may be up to 350 ng/m 3
(Table 21.1). Atmosphere above seas and oceans contains variable I amounts; its
mean value are as follows (in ng/m 3 ): Japanese Sea, 200; Baltic Sea, 1,090; and Black
Sea, up to 48,000.
Organic I species dominate in air, and may be up to about 90% of its total concentration. Most probably these I species are methyl I, which is easily transferred to
inorganic I forms. All iodine species, including its radionuclides, can be transported
by air for relatively long distances. Radioactive I may be formed naturally, due to
chemical reactions, high in the atmosphere, and may be changed to a stable element
very quickly.
The oceans are the most important source of natural I in the air, water, and soil.
Iodine in the oceans enters the air from sea spray or as gases. In the air, I can combine with water or with particles, and in such forms falls to the ground, from which
it is easily emitted. Thus, its emission from the surface of seawater, volatilization
from soils, and volcanic gases control its concentration in the atmosphere. Average
I deposition in seacoast regions is estimated at 7 mg/m 2 /yr (Fuge and Jonhson vide
Kabata-Pendias 2011).
21.5 PLANTS
Iodine has not been shown to be essential to plants, although there are some reports
on its stimulating impact on plant growth. Its toxic concentration in nutrient solution is higher than soluble I content of soils, and therefore its toxicity has not been
observed under natural field conditions. However, there are some reports on I toxicity to rice plants grown in submerged paddy fields (Yuita vide Kabata-Pendias 2011).
Also, in some polluted regions, I toxicity symptoms may be observed in plants.