@misc{oai:repo.qst.go.jp:00059966,
 author = {Muramatsu, Yasuyuki and Yoshida, Satoshi and Fehn, Udo and Amachi, Seigo and 村松 康行 and 吉田 聡 and 天知 誠吾},
 month = {Sep},
 note = {Iodine is a biophilic element and play an important role in thyroid function. Nearly 90% of iodine is concentrated in a small organ, thyroid gland (ca. 20 g), in human body. Iodine is essential not only for mammalian but also for other animals such as fishes and amphibian. However, it is not known when and how iodine was utilized through the evolution of organisms in the earth history. In the early history of the earth, iodine is thought to be released from the mantle into the atmosphere due to degassing and it was dissolved in seawater when the ocean was born. Iodine concentration in the primeval seawater should be much higher than the present level (we estimated about 100 times higher), because of the absence of the accumulation processes into the ocean sediments under anoxic condition. After the oxygen level increased due to the appearance of photosynthetic organisms (e.g. cyanobacteria), iodine accumulation in ocean sediments might be started. 
In this study we have carried out iodine analysis in different geochemical, biological and nutritional materials and also performed radiotracer experiments to understand its levels and behavior in the environment. We also studied the age and origin of iodine-rich brines (typically containing methane) in Chiba, Japan, where one third of world iodine is producing. Some important pathways and mechanisms to understand biogeochemical cycle of iodine are discussed in this paper.
Based on our analytical data for iodine in many different materials, which make up the earth crust and are present in the environment, the inventory of iodine in the crust was calculated. Nearly 70% of the iodine is present in oceanic sediments, followed by continental sedimentary rocks (ca. 27%). These enrichments are expected to be related to the activities of marine organisms. 
Iodine concentrations in soil samples collected from different places ranged between 0.5 and 60 ppm. These values are much higher than those in their parent materials (mostly <0.1ppm), suggesting iodine has been accumulated in soil through the atmospheric deposition during its formation. (Iodine in the atmosphere is evaporated from the ocean.) We found through radiotracer experiments that microorganisms play an important role in the fixation processes of iodine in soil under oxic condition. Participation of microorganisms is also important in the desorption of iodine from soil under flooded condition (low Eh), resulting low iodine concentrations in rice paddy soils. 
We also found that volatile organic iodine was produced microbiologically during incubation of soil solution, seawater and bacterial cell suspension. It is interesting to note that the organic iodine production decreased markedly when the samples were sterilized (filtering or autoclaving). These results suggest that microorganisms play an essential role in the fate of iodine in the environment.
Analytical results for many elements and some isotopes in iodine-rich brines from Chiba (depth: ca.1000m) showed that these fluids were derived from organic-rich marine sediments. The 129I age obtained for these samples (about 50 Ma) is much older than that of the current reservoir formations  (1-2 Ma). This suggests that the iodine enrichment in the brines was caused by remobilization from subducting marine sediments associated with the release of pore waters with high concentrations of iodine (and methane) in the fore-arc area. Iodine-rich brine may provide useful information on the cycling of iodine and relevant elements in the global environment and also in the paleo-environment., 第16国際環境生物地球化学シンポジウム},
 title = {Biogeochemical Cycle of Iodine-from the Earth's Mantle to Human Thyroid},
 year = {2003}
}