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The Iodine Group | |
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FUGE
Soils and Iodine DeficiencyFuge R from Essentials of Medical Geology: Impacts of the Natural Environment on Public Health, Selinus O (ed), Elsevier Academic Press, 2005, pp 417-33.
"In the lithosphere iodine is an ultra-trace element; its crustal abundance is estimated to be 0.25 mg kg-1.... Due to the large ionic radius of the iodide ion (220 pm), it is thought unlikely that iodine enters the crystal lattices of most rock-forming minerals.... Recent sediments of marine origin can be extremely enriched in iodine with concentrations of up to 20,00 mg kg-1.... [Soils show] a very broad range of concentrations from <0.1-150mg kg-1. The iodine content of soils is generally considerably higher than the rocks from which they derive. Most geochemists agree that the majority of the iodine in soils is derived from the atmosphere and ultimately the marine environment.... Soil iodine geochemistry reflects both the input of iodine and the ability of the soil to retain it.... Whereas organic matter has been shown to be the major contributor to the retention of soil iodine, it has also been suggested that iron and aluminum oxides play an important role in soil iodine retention."
"Seawater is by far the biggest reservoir of iodine; its average concentration is about 60 mcg L-1.... Inorganic iodine is essentially present in two forms, the iodide anion, I-, and the iodate anion, IO3-.... It has long been suggested that some iodine in seawater is present as an organic phase, and recently it has been found that in some coastal waters dissolved organic iodine can constitute up to 40% of the total iodine content.... One of the substances identified, methyl iodide (CH3I), is of interest due to its volatility and possible role in the transfer of iodine from the oceans to the atmosphere. It is generally held that the iodide ion is preferentially incorporated into the organisms; however, it has been demonstrated that phytoplankton can take in iodate."
"When iodine is strongly sorbed in most soils, it will not be readily bioavailable. Therefore, the presence of high iodine concentrations in soil does not necessarily mean that plants growing in the soil will incorporate large concentrations of iodine; indeed, it has been shown that there is no correlation between the iodine content of soils and the plants growing on them. This is particularly important when considering the distribution of IDD. An additional consideration is that iodine in high concentrations has been shown to be toxic to most plants....
"In most circumstances the major pathway of elements into plants in through the root system followed by translocation to the upper parts of the plant. For iodine it has been shown experimentally that it can be taken in through the root system of plants, with the iodide ion more readily incorporated than iodate. However, it has also been demonstrated that there is little translocation from the roots to the aerial parts of the plant. In some circumstances high concentrations of iodine have been shown to occur in rice grown on flooded soil, which leads to Akagare disease...
"From these considerations it seems likely that root uptake of iodine is relatively unimportant for the overall iodine content of plants. It is probable that the most important pathway into plants is from the atmosphere by direct absorption. Experiments utilizing radioactive isotopes of iodine have demonstrated that plant leaves can absorb this iodine, and it has been found that the absorption of gaseous iodine by leaves increases with increasing humidity. This is probably due to increased opening of the leaf stomata. Iodine absorbed through the leaf can be translocated through the rest of the plant, albeit slowly."
Transport of Iodine in the environment and pathways into the biosphereFuge R Denver Annual Meeting, 2002. Paper No. 197-9
" Iodine is an essential element for humans being an important component of the thyroid hormone thyroxine; deficiency of dietary iodine leads to a series of diseases collectively known as iodine deficiency disorders or IDD. It is vital, therefore, to understand its geochemistry and more particularly its pathways into the biosphere. The oceans represent the largest reservoir of iodine on the Earth and virtually all iodine in the terrestrial environment derives from the oceans by way of the atmosphere. Iodine is volatilised from the sea in several forms with CH3I probably being the most important of these. This volatilised iodine is deposited on land by wet and dry precipitation and consequently soils from near coastal environments are enriched in iodine with soils remote from the sea being depleted. The traditional view of the distribution of IDD is coloured by this generalised view of the transport of iodine from the marine to terrestrial environments. However, the direct marine influence on the terrestrial environment may well be limited with concentrations of iodine in soils around 80 to 100 km from the coast being fairly similar to those from central continental regions. It is also assumed that iodine in soils is transferred to plants and that these, in turn, represent a major pathway of iodine into animals and humans. However, the soil to plant concentration factor for iodine has been shown to be low, due to the strong sorption of iodine by various soil components. Little iodine in soils has been found to be easily leachable and no correlation of soil and plant iodine has been demonstrated. In addition it has been shown that little iodine is translocated from the roots of plants to the aerial parts and it is likely that most is taken in from the atmosphere through the stomata, which would require iodine to be volatilised from soils in areas remote from marine influence. Such volatilisation may be limited due to iodine being strongly bound in soil. With IDD recently re-occurring in many affluent western European countries it is time to re-assess the environmental cycle of iodine."
The role of volatility in the distribution of iodine in the secondary environmentFuge R Applied geochemistry. 1990, 5:3, pp. 357-360 [citation only]
Iodine in waters: possible links with endemic goitreFuge R Applied geochemistry. 1989, 4:2, pp. 203-208 [citation only]
Iodine in the soils of North Derbyshire.Fuge, R; Long, AM [abstract only] "Derbyshire was one of the best known centres of endemic goitre in Great Britain. Some 160 km from the coast in the direction of the prevailing wind, topsoils in the area are generally low in iodine (mean = 5.44 mg l/kg). Weathered rocks and soils are richer in iodine than the unweathered bedrocks, with soils developed over limestones being richer than those over sandstones, shales and dolomites. Highest iodine contents in soil profiles over limestones occur in the upper horizons while over sandstones, iodine concentrates in the lower horizons. The major cause of endemic goitre in north Derbyshire is likely to be relatively low levels of iodine, while the calcium rich soils of the area may contribute by reducing plant iodine uptake."
Sources of halogens in the environment, influences on human and animal health.Fuge, R Environmental Geochemistry and Health. Vol. 10, no. 2, pp. 51-61. 1988. [abstract only]
"Of the halogens, fluorine has the highest crustal abundance while iodine has the lowest, however, chlorine is by far the most abundant halogen in the cosmos. The geochemistries of the four naturally occurring halogens have some similarities with fluorine, chlorine and bromine being classified as lithophile elements while iodine is more chalcophile in nature. Bromine and iodine behave in a similar fashion in the secondary environment and could be classified as biophile elements being concentrated in organic matter. Chlorine, bromine and iodine are strongly enriched in the sea while iodine and to a lesser extent bromine are further concentrated in the marine algae."
The distribution of chlorine and iodine in soil in the vicinity of lead mining and smelting operations, Bixby area, S.E. Missouri, U.S.A.Fuge, R; Andrews, MJ; Clevenger, TE; Davies,
BE; Gale, NL; Paveley, CF; Wixson, BG
[abstract only] "Iodine and Cl are enriched in soils in the vicinity of the Magmont and Buick lead mines near Bixby, southeastern Missouri. The enrichments, up to 5.6 ppm I and 305 ppm Cl, are against regional backgrounds of 1.26 ppm I and 41 ppm Cl. The area of highest I and Cl is thought to reflect a zone of base metal sulphide mineralization occurring about 400 m below the surface. Iodine and Cl are also enriched in soils immediately adjacent to a tailings pond, hence these elements would appear to be leached from this source. A zone of enhanced I values (up to 2.65 ppm I) to the north of a lead smelter is superimposed on a much larger zone of lead enrichment (up to 12,000 ppm Pb) and is thought to represent I released from sulphide ores on smelting."
The geochemistry of iodine - a review.Fuge R, Johnson CC Environmental Geochemistry and Health. Vol. 8, no. 2, pp. 31-54. 1986. [abstract only]
"Iodine has long been recognised as an important element environmentally. Despite this there are many gaps in our knowledge of its geochemistry and even where information is available much of this is based on old data which, in the light of recent data, are suspect. Iodine forms few independent minerals and is unlikely to enter most rock-forming minerals. In igneous rocks its concentration is fairly uniform and averages 0.24 mg/kg. Sedimentary rocks tend to have higher concentrations with average iodine contents of:- recent sediments 5-200 mg/kg, carbonates 2.7 mg/kg, shales 2.3 mg/kg and sandstones 0.8 mg/kg. Organic-rich sediments are particularly enriched in iodine. Soils, generally, are much richer in iodine than the parent rocks with the actual level being decided mainly by soil type and locality. Little soil iodine is water-soluble and much iodine is thought to be associated with organic matter, clays and aluminium and iron oxides. Most iodine in soils is derived from the atmosphere where, in turn, it has been derived from the oceans. Seawater has a mean iodine content of 58 mu g/L while non-saline surface waters have lower and very variable levels. Subsurface brines and mineral waters are generally strongly enriched in iodine."
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