KEYNOTE Volatilisation, the key to iodine geochemistry

Iodine is an essential element for humans and animals and, consequently, there is major interest in its geochemistry. The key component in the geochemical cycle of iodine is its volatility. The oceans represent the most... [ view full abstract ]

Iodine is an essential element for humans and animals and, consequently, there is major interest in its geochemistry. The key component in the geochemical cycle of iodine is its volatility. The oceans represent the most important reservoir in the global iodine cycle, it being volatilised from the marine environment as a series of iodo-organic compounds together with elemental iodine, both of which are derived from biological and inorganic sources. Marine-derived iodine is the most important source of this element in the terrestrial environment. However, determination of iodine in soils has demonstrated that the major marine influence stretches to only 80 km from the coast. Elevated concentrations of atmospheric iodine in inland areas highlights the importance of its volatilisation from the terrestrial environment. Volatilisation of iodine has been shown to occur in soils, most particularly from waterlogged soils and wetlands, with much of the iodine emitted as CH3I, which is derived from microbial action. Higher plants have also been found to emit CH3I, possibly as a detoxification mechanism.
It has been found that emissions from iodine-rich marshy areas in the English Fenlands of the UK enrich iodine in soils up to 40 km from the source, thus demonstrating that terrestrially-derived iodine can be a significant source of that element in soils and, potentially, the biosphere.