Abstract
Iodine is one of the essential trace elements in the human body, and excessive or insufficient intake will affect human health. To ensure the safety of drinking water resources, the spatial distribution of iodine content and migration enrichment factors in shallow underground salty water in Tianjin coastal area were studied. The results show that the iodide content of shallow groundwater ranges from ND to 1320 μg/L, and high iodine groundwater (100-300 μg/L) and ultra-high iodine groundwater (>300 μg/L) account for 37.5%, distributed in the east, west, central and south of the study area; iodine-deficient groundwater (＜25 μg/L) accounts for 10%, and iodine-suitable groundwater (25-100 μg/L) accounts for 15%. From north to south and from northwest to southeast, the shallow groundwater in the study area changed from freshwater and brackish water to saline and salt water; the I- concentrations in freshwater, brackish water, and saltwater were significantly different, and the I- concentrations tended to increase with the increase of TDS concentration; the main hydrochemical types in this direction changed from HCO3·Ca-Na→Cl·SO4-Na·Mg→HCO3·Cl-Na·Ca→Cl·HCO3-Na→Cl-Na type shift; high iodine and ultra-high iodine groundwater chemistry types are mainly Cl-Na types, Cl·HCO3-Na type and HCO3-Ca·Na type. The main source of iodine in groundwater is marine sediments, and its enrichment mechanism is as follows: stronger reducing environment and groundwater flow promote the dissolution of carbonates containing Ca2+, HCO3-, SO42- and sulfate minerals, such as gypsum and manganese nitrate; sedimentary iodine is released in the process of dissolution of marine sediments and reduced to I-; I- migrates with the flow of groundwater; in the eastern part of the study area, the poor permeability of the In the eastern part of the study area, mucky clay is the main soil structure, and groundwater flow is blocked, so I- is enriched here, and the concentration increases under strong evaporation and concentration.