Iodine in soil

Van Vleit et al. [9] have described a semiautomatic spectrophotometric method using a Technicon Autoanalyser for the determination of iodine in soil extracts. The method has a coefficient of variation of 2.1% at the 8.6mg L 1 iodine level to 6.1% at the 1.4mg L-1 iodine level. 

Iodine is essential in the mammalian diet to produce the thyroid hormone thyroxine deficiency in humans causes goitre. Collectively, deficiencies of iodine, iron, zinc and vitamin A in humans are thought to be at least as widespread and debilitating as calorie deficiencies (Welch and Graham, 1999). The main source of iodine in soils is oceanic salts rather than parent rock, and so deficiency is most widespread in areas remote from the sea (Fuge, 1996). In principle deficiency is easily corrected with dairy supplements. However in practice this is not always feasible. Addition of iodate to irrigation water has successfully corrected widespread iodine deficiency in parts of China where the usual methods of supplementation had failed (Cao et al., 1994 Jiang et al 1997). However there is not much information on the behaviour of iodine in soil and water systems. 

Yuita K. 1992. Dynamics of iodine, bromine, and chlorine in soil. II. Chemical forms of iodine in soil solutions. Soil Science and Plant Nutrition 38 281-287. 

Van Vliet et al. [15] have described a semi-automated procedure for the determination of iodine in soils. The soil sample is digested with 2 N sodium hydroxide, and then the soil is centrifuged off. The resulting solution is digested with perchloric and nitric acid (2 1 v/v) at 265 °C until clear. Iodine is determined in this solution by a method based on the oxidation of arsenic III by cerium IV 3 - 5 ppm mg/kg added to soil was recovered at the 98% level. 

Much has been written in recent years about atmospheric inputs to the soil since the acid rain problem has been recognised. Soils receive both wet deposition, ie, precipitation as rain or snow and dry deposition in which aerosols are deposited on the surface. Although precipitation is very dilute it can be an important source for some elements, cyclic salts which are derived from the oceans and transported to the land surface in the normal hydrological cycling of elements. Fuge and Johnson (1986) concluded that most iodine in soils is derived from the atmosphere and, hence, the oceans. Normally, however, rain makes only a very small contribution to the composi-... 

Fordyce FM, Johnson CC, Navaratna UR, Appleton JD, Dissanayake CB. Selenimn and iodine in soil, rice and drinking water in relation to endemic goitre in Sri Lanka. Sd Total Environ 2000 263 127-41. 

Letunova et al. (1987) calculated that the microorganism biomass contains from 0.012 to 3.24% of the iodine present in surface soil layers, though some fungi that occur in soils are known to accumulate much higher amounts of iodine. Soil acids favor iodine sorption by soil components such as organic matter, hydrous oxides of iron and aluminum. However, liming is known to reduce the solubility of iodides, iodates and iodine in soils and thus also to reduce iodine bioavailability. 

The research objectives of this study are to evaluate the distribution of various iodine species in some soils and sediments in the United States, and to understand the extent and rate of interaction of iodine species (i.e., iodide, iodate, and organoiodine in the form of 4-iodoanihne) with sediment from nuclear facilities in the US Department of Energy (DOE) complex, where major releases of radionuclides, including I, have occurred (NRC, 2000). In this study, we infer important aspects of the environmental behavior of I, based on the similarities and differences between this radionuclide and stable iodine. Salient insights and future work regarding geochemical cycling of iodine in soils are then summarized. 

However, some workers have found the speciation of iodine in soil solution to be somewhat more complex,... 

Investigation Of Iodine Concentration In Salt, Water Soil Along The Coast Of Zhejiang, China. J Zhejiang Univ Sci B., Vol.6, No.12, pp 1200-1205, ISSN 1862-1783 Mani, D., Gnaneshwar Rao T., Balaram, V, Dayal, A.M. Kumar, B. (2007). Rapid Determination Of Iodine In Soils Using Inductively Coupled Plasma Mass Spectrometry. Current Science, Vol.93, No. 9,10, p>p 1219-1221, ISSN 0011-3891... 

It is widely believed that iodine in soil is derived from iodine in the ocean rather than from iodine in the rock. This implies that the specific activity of I in the iodine of human thyroids should be the same as that in the oceans. If, however, the iodine in soil originates from weathering of rocks (as is the case with other heavy trace elements), then the I specific activity in thyroids should be much lower. It now appears that only a small fraction of the iodine in soil is of oceanic origin. Most calculations of very long-term effects of I on human health are therefore considered to have resulted in overestimated figures (Cohen 1985). 

Mobile radioisotopes are available to immediately interact with soil compo-" nents while the others will reside in discrete fallout particles until they are released by weathering processes. There is an immense body of literatures dedicated to studying the uptake of mobile fallout Cs by clays (i.e., Poinssot et al., 1999) and the persistent but capricious retention of small amounts of fallout iodine in soils (Bors et al., 1988). 

Bors, J., R. Martens, and W. Kuhn. 1988. Studies on the role of natural and anthropogenic organic substances in the mobility of radio-iodine in soils. Radiochimica Acta. 44/45 201-206. 

Yamada, H., Kiriyama,T., andYonebayashi, K. (1996). Determination of total iodine in soils by inductively coupled plasma mass spectrometry. Soil Sci. Plant Nut. 42(4), 859. 

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