Theoretical evaluation of iodine and selenium speciation in the natural waters of iodine-deficient territories

Water migration of iodine, selenium are in many cases directly related to manifestation of thyroid pathologies, in particular, the endemic goiter. The main aim was to evaluate species and conditions of migration of these elements in natural waters from different water-bearing rocks in areas with a natural iodine deficiency. Evaluation of iodine and selenium species in aqueous solutions has been carried out by thermodynamic modeling basing on chemical composition of 81 water samples taken in the Bryansk region in the period of 2015-2017. The study has showed that the predominant species of iodine in the natural waters is iodide-ion (89%), which may also associate with typomorphic ions (Ca, Mg, Na, K, Sr) forming mineral complexes with them. In the latter state iodine may be removed from solution by fixation on a carbonate barrier. Selenium dominates in natural waters as hydroselenide ion (91%). In the presence of a significant amount of iron, this trace element may form the FeSe mineral phase which may be fixed in reduction conditions.