Study On The Migration And Enrichment Of Iodine And The Impact Of Exogenous Organic Caron In The Groundwater System Of Datong Basin,China

Iodine is an important component of synthetic thyroxine and is a necessary micronutrient for the human body.Two thirds of the iodine in the body is found in the thyroid gland.Insufficient iodine intake can lead to several iodine deficiency disorders,such as goiter,cretinism and even sterility,while excessive iodine can inhibit several thyroid processes and cause thyroid autoimmunity?Hashimoto's thyroidities?and even some thyroid cancers.The high iodine areas in China are mainly lacated in the Yellow Huaihai Plain,arid inland basin and casstal areas.Datong basin is a typical arid inland basin in China,some studies have shown that there is an obvious occurrence of high iodine groundwater in basin.The reason is that periodic irrigation can lead to cyclical changes on oxidation-reduction environment in shallow groundwater,and also lead to exogenous substances input,to provide additional carbon for microbial in shallow groundwater,causing the degradation of iodine deposits,and then cause the migration and release of iodine in shallow groundwater system.In this study,the Datong Basin in Shanxi Province is selected as the research area,and the typical high-iodine groundwater system is the research object.Combine with the influence of hydrogeology and irrigation activities on shallow groundwater system in the study area.Through field sampling and indoor micro experiment,we analysis the different chemical speciation of iodine in natural high iodine groundwater and the source of iodine in sediments.Under different redox conditions,research the effects of exogenous organic carbon input on iodine migration in shallow aquifers.It is necessary to reduce the harm to human health caused by drinking high iodine groundwater,to ensure the safety of drinking water,relieving the shortage of lacal water supply and provide scientific basis for the proper treatment of high iodine groundwater.The main findings obtained are as follows:1.The variation range of iodine concentration in groundwater at Datong Basin was between 8.170?g/L and 1067?g/L,with an average value of 175.0?g/L.The iodine concentration in groundwater is gradually increased from the edge of the mountain to the center of the basin,and all the high concentration iodine samples are collected in the center of the basin.Vertical,the iodine content of shallow groundwater samples is significantly higher than that of the deep groundwater.2.The hydrogeochemistry types of high iodine groundwater in the study area are mainly Na-HCO₃ and Na-Cl??SO₄?,and the type of low-iodine groundwater is mainly Ca-HCO₃.The conditions of weak alkali?pH?is beneficial to the enrichment of iodine in groundwater,and the occurrence of iodine is mainly I^-.The positive correlation between iodine and TDS,EC and Cl in groundwater shows that evaporation is the main factor of iodine enrichment in shallow groundwater.3.Total iodine contents in the sediments from the borehole DXZ-II variaed from<0.01 to 1.78?g/g,with the average is 0.29?g/g,and elevated iodine concentration was found at the depth of 6.1²2.9m,86.2¹02.0m,156.0²00.4m,224.2²52.0m and272.0³00.0m.The content of iodine in the shallow layer and middle depth is basically consistent with the vertical distribution of iodine groundwater.According to the positive correlation between TOC and iodine content,we can see that the organic matter rich in clay sediments is the main source of iodine in groundwater system.4.Under the influence of agricultural irrigation activities,the redox environment of shallow groundwater system will change periodically.Under the condition of reduction,the microorganism will uses the exogenous organic carbon to reduce the iron mineral phase in the sediment,causing the release of iodine in the iron ore phase,and then form the high iodine groundwater.