The iodine cycle: iodine cycling in the ecosphere, and its relevance to Tasmania - consortium environmental iodine research

The major repository of iodine and its source to the other domains in Earth's ecosphere are the oceans, and in particular their sediments. The planet's land surfaces are universally low in this element; they and associated life forms rely on the delivery of iodine from the ocean via the atmosphere. The many different chemical forms in which iodine is found are instrumental in facilitating its mobility in the ecosphere. Just as oceans have most of the iodine, so it is that certain marine life forms are strong concentrators of this element. The transfer of gaseous forms of iodine across the sea-air boundary is pivotal in instigating the efficient transfer from sea to air to land. In the lower levels of the atmosphere, iodine is an important agent in the destruction of ozone. Fortunately, it does not have a long lifetime in the atmosphere, falling back to land and sea in rain or as dry deposition of fine particles. Run-off from the land in streams or subsurface aquifers returns the element to the sea. In the final section, we use the general knowledge of iodine cycling to estimate its transfer to the island of Tasmania. Not much information is available about the distribution of iodine in the natural environment of the island. However, we have inferred iodine's transfer in wet and dry deposition from the latest information on rainfall and atmospheric circulation patterns, and estimated its retention regionally on the basis of soil types and their ability to hold the element. Finally, we have observed a close relation between our designated 'iodine-deficient' areas, and the occurrence of iodine deficiency diseases in livestock