Controls on the spatial distribution of iodine in groundwater in the Hebei Plain, China.

In the Hebei Plain of North China, 70% of the inhabitants depend on groundwater for drinking water. Little is known regarding high-iodine concentrations in groundwater because there have been few systematic studies on high levels of iodine in groundwater in this region. To help identify the mechanisms that control the spatial distribution of iodine in groundwater, 61 samples of shallow groundwater and 161 samples of deep groundwater were collected along a sample section from Taihang Mountain to the Bo Sea. There were four pockets of high-iodine concentrations along the sample section. As the groundwater depth increased, the ratio of undetected iodine decreased, and the ratio of high-iodine concentrations increased. The high-iodine concentrations in the groundwater reflect the geological and sedimentary settings, and were mainly controlled by pH and Eh. Iodine concentrations were particularly high when the pH was between 7.3 and 8.5, and there was an inflection point at 150 μg/L in the curve of the relationship between iodine concentrations and Eh.