Iodine Speciation and its Potential Influence on Iodine Enrichment in Groundwater from North China Plain

In order to reveal the pattern of spatial distribution of iodine in groundwater at North China Plain (NCP), a total of 136 groundwater samples were collected along the regional groundwater flow paths. The results showed that groundwater iodine ranged from 1.51 to 1106μg/L, and 31.4% of the samples have iodine concentrations higher than 150μg/L. High iodine groundwater samples are mainly observed in the coastal area of Bohai sea, and well depths greater than 350 m. The results of iodine speciation analysis showed that groundwater iodide, iodate and organic iodine had the ranges of <0.025∼854μg/L, <0.035∼293μg/L and <10∼296μg/L, respectively, indicating that iodide is the dominant species of iodine in groundwater at NCP. Iodate is only observed in groundwater with Eh values higher than 0mV, suggesting that groundwater redox condition is the main factor controlling iodine speciation. The widespread sub-reducing/reducing condition and low affinity of iodide are the two main factors promoting the iodine enrichment in groundwater.