Iodine

Iodine is one of the halogens, the most reactive group of elements in the periodic table. This group includes fluorine, chlorine, bromine, and iodine. The halogen's are prominent anions in the environment, forming largely ionic molecules. They are powerful oxidizers as neutral atom free radicals. The halogens form diatomic molecules that are gases at normal temperatures and pressures and therefore are mobile and play significant roles in the atmosphere, hydrosphere, and biosphere.

Iodine, as a halogen, needs an electron to complete its octet. The size, weight, and electron density of iodine produces weak chemical bonds. All of the natural halogens can and do replace iodine from almost any molecule. Iodine is continually losing its shared electron and is forced out as either the gasous/solid mobile diatomic molecule or the reactive free radical.  Iodine ends up at the interfaces, aqueous/sediment and gasous/solid, seeking an electron with little hope of ever maintaining it once it is acquired.

Recent research indicates most or all of the iodine in the soil is related to hydrocarbons. These compounds are a complex mixture of iodoorganics ranging from iodomethane to humic-iodine.

Soil iodine enrichments and light hydrocarbon seepage have been directly correlated.  Iodine enrichments over hydrocarbon seepage sometimes exceed 10 times the average background.  When iodine is organically bound to hydrogen, the hydrocarbons become immobile. The iodine then congregates at this source of electrons. If the hydrocarbons stop, the iodine disperses continuing its search for another electron source.