Английская Википедия:Iodine cycle
The iodine cycle is a biogeochemical cycle that primarily consists of natural[1] and biological processes[3] that exchange iodine through the lithosphere, hydrosphere, and atmosphere.[3][2] Iodine exists in many forms, but in the environment, it generally has an oxidation state of -1, 0, or +5.[1]
Oceanic cycling
Шаблон:Biogeochemical cycle sidebar
Iodine in the ocean exists mostly in oceanic sediments and seawater.[4] During subduction of oceanic crust and seawater, most of the iodine cycles into seawater through brine, while a minor amount is cycled into the mantle.[4] Marine biota, including seaweed and fish, accumulate iodine from the seawater and return it during decomposition.[2] Sedimentation of oceanic iodine replenishes the ocean sediment sink. [1]
The losses of iodine from the oceanic sink are to the atmospheric sink.[1] Sea spray aerosolization accounts for a portion of this loss.[2] However, the majority of the iodine cycled into the atmosphere occurs through biological conversion of iodide and iodate to methyl forms, primarily methyl iodide.[3] Algae, phytoplankton, and bacteria are involved in reducing the stable Iodate ion to iodide,[5] and different species produce volatile methyl iodide which leaves the oceans and forms aerosols in the atmosphere.[3]
Terrestrial cycling
Iodine rarely occurs naturally in mineral form, so it comprises a very small portion of rocks by mass.[2] Sedimentary rocks have higher concentrations of iodine compared to metamorphic and igneous rocks.[4] Due to the low concentration of iodine in rocks, weathering is a minor flux of iodine to soils and the freshwater hydrosphere.[1]
Soils contain a much higher concentration of iodine compared to their parent rock, though most of it is bound to organic and inorganic matter, potentially due to microbial activity.[4] The major source of iodine to soils is through dry and wet deposition of aerosolized iodine in the atmosphere.[1] Due to the high production of atmospheric iodine from the oceans, both the concentration of iodine and the flux of iodine to soils is greatest near coastal regions.[1] Plants uptake iodine from the soil through their roots and return the iodine when they decompose.[2] Fauna that consume plants may uptake this iodine but similarly return it to soils upon decomposition.[2] Some iodine may also be cycled into the freshwater hydrosphere through leaching and runoff, where it may return to the oceans.[1]
Similar to oceanic iodine, the majority of iodine cycled out of soil is volatilized through conversion to methyl forms of iodine by bacteria.[3] Unlike ocean volatilization, however, bacteria are thought to be the only organisms responsible for volatilization in soils.[4]
Anthropogenic influences
Iodine is a necessary trace nutrient for human health and is used as a product for various industries.[3] Iodine intended for human use and consumption is taken from brines, which accounts for a minor perturbation to the global iodine cycle.[1] A much larger anthropogenic impact is through the burning of fossil fuels, which releases iodine into the atmosphere.[1]
Iodine-129, a radioisotope of iodine, is a waste product of nuclear power generation and weapons testing.[3] Unless present in high concentrations, I-129 likely does not present danger to human health.[6] Early research has attempted to use the I-129/I-127 ratio as a tracer for the iodine cycle.[6]
References
- ↑ 1,00 1,01 1,02 1,03 1,04 1,05 1,06 1,07 1,08 1,09 1,10 1,11 1,12 1,13 1,14 1,15 1,16 1,17 Шаблон:Cite journal
- ↑ 2,0 2,1 2,2 2,3 2,4 2,5 2,6 2,7 Шаблон:Cite journal
- ↑ 3,0 3,1 3,2 3,3 3,4 3,5 3,6 3,7 3,8 Шаблон:Cite journal
- ↑ 4,0 4,1 4,2 4,3 4,4 4,5 4,6 4,7 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ 6,0 6,1 Шаблон:Cite journal
