The Hydrogeochemical Characteristics of High Iodine and Fluoride Groundwater in the Hetao Plain, Inner Mongolia

Abstract Twenty groundwater samples and two surface water samples were collected to determine the occurrence and distribution of iodine and fluoride in groundwater in the area of Hangjinhouqi, the Hetao Plain, Inner Mongolia. Currently, 65% and 50% of samples exceeded the Chinese standard (I=150 μg/L, F=1 mg/L) for drinking water for iodine and fluoride, respectively. No correlation has been shown between I and F, although the spatial distribution of high iodine and high fluoride groundwater samples overlaps, with 80% of the high fluoride groundwater samples located in the high iodine areas. Different enrichment mechanisms of fluoride and iodine are involved. Water-rock interaction processes are at the origin of fluoride rich-groundwater, whereas evaporation of shallow groundwater and the oxidation by microorganisms of elevated organic matter content in deep groundwater contribute to the enrichment of iodine.