The mechanism of high iodine groundwater driven by human activities: a case study of Fuzhou City

Drinking high iodine water for a long time can cause thyroid dysfunction and pose a threat to human health. We selected high iodine groundwater in Fuzhou as the research object, and collected 42 groups of groundwater samples from different land use types. The spatial characteristics and genetic mechanisms of iodine in shallow groundwater were studied by using statistical analysis and ion ratio analysis. The results showed that the average content of iodine in local groundwater was 0.10 mg/L (0.008 0~0.52 mg/L). The distribution characteristics of iodine were inland low-coastal high, mountain low-plain high, and rural low-urban high. High iodine groundwater samples accounted for 19.1％, and were predominantly distributed in the main urban areas along the Minjiang River, eastern Fuqing and Pingtan coastal areas. The Quaternary alluvial and marine sediments provide a natural material sources for iodine enrichment in groundwater. Moreover, the reduced groundwater environment and long retention time are natural conditions of iodine enrichment in groundwater. As the spatial distribution of high iodine groundwater is highly correlated with the areas of high population density, it is suggested that high iodine domestic sewage discharged from human activities plays a significant role in the formation mechanism of high iodine groundwater.