Partition of iodine (¹²?I and ¹²?I) isotopes in soils and marine sediments |
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Authors: | Hansen Violeta Roos Per Aldahan Ala Hou Xiaolin Possnert Göran |
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Institution: | a Risø National Laboratory for Sustainable Energy, NUK-202, Technical University of Denmark, Frederiksborgvej 399, P.O.B. 49, DK-4000 Roskilde, Denmark b Department of Earth Science, Uppsala University, SE-758 36 Uppsala, Sweden c Department of Geology, United Arab Emirates University, Al Ain, United Arab Emirates d Tandem Laboratory, Uppsala University, SE-751 21 Uppsala, Sweden |
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Abstract: | Natural organic matter, such as humic and fulvic acids and humin, plays a key role in determining the fate and mobility of radioiodine in soil and sediments. The radioisotope 129I is continuously produced and released from nuclear fuel reprocessing plants, and as a biophilic element, its environmental mobility is strongly linked to organic matter.Due to its long half-life (15.7 million years), 129I builds up in the environment and can be traced since the beginning of the nuclear era in reservoirs such as soils and marine sediments. Nevertheless, partition of the isotope between the different types of organic matter in soil and sediment is rarely explored. Here we present a sequential extraction of 129I and 127I chemical forms encountered in a Danish soil, a soil reference material (IAEA-375), an anoxic marine sediment from Southern Norway and an oxic sediment from the Barents Sea. The different forms of iodine are related to water soluble, exchangeable, carbonates, oxides as well as iodine bound to humic acid, fulvic acid and to humin and minerals. This is the first study to identify 129I in humic and fulvic acid and humin. The results show that 30-56% of the total 127I and 42-60% of the total 129I are associated with organic matter in soil and sediment samples. At a soil/sediment pH below 5.0-5.5, 127I and 129I in the organic fraction associate primarily with the humic acid while at soil/sediment pH > 6 129I was mostly found to be bound to fulvic acid. Anoxic conditions seem to increase the mobility and availability of iodine compared to oxic, while subaerial conditions (soils) reduces the availability of water soluble fraction compared to subaqueous (marine) conditions. |
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Keywords: | Iodine-129 127 Speciation Iodine humic substances ICP-MS AMS |
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