Abstract:

In order to understand the sources of iodide in shallow groundwater in these typical aquaculture areas of the Pearl River delta as well as the health risks associated with drinking. This study analyzed a total of 21 representative samples from three different types of water sources: fish ponds, sewage treatment ponds, and groundwater in typical freshwater aquaculture areas of the Pearl River  delta. The results indicated that shallow groundwater in the study area had a water chemistry type primarily composed of Ca2+·HCO3- type with iodide concentrations ranging from 2-343 μg/L of the monitored sites. 33.3% of the monitored sites were high iodine type water sources that were concentrated and dispersed in the western part of the study area. According to principal component analysis, iodine fugacity in groundwater was encouraged by the neutral to mildly alkaline reducing environment, and the degradation and percolation of iodine-rich organic materials from fish pond waste may have made the situation worse. The major causes of shallow, highly iodized groundwater may include degradation of organic matter in carbonate-rich rocks, urbanization with reduced effluent, and waste leachate leaks. The results of water quality evaluation showed that 16.7% of the surface water (fish ponds, sewage treatment ponds) in the study area was Class Ⅳ, and the chemical oxygen demand (CODMn) and total nitrogen (TN) were the main factors exceeding the standard. Although the pH and iodide levels in some areas of shallow groundwater exceed the recommended levels, overall water quality is satisfactory, with the worst groundwater quality being Grade Ⅲ. The examination of the health risks associated with groundwater revealed that while adults are at minimal risk from high iodine drinking water, children have a risk entropy of J4 groundwater sources that is larger than 1.0. It is suggested to strengthen the routine monitoring of residential drinking well J4 iodide concentration to ensure the health of children drinking water.

Key words: Pearl River delta, water quality evaluation, iodide, health risk, shallow groundwater, surface water