Abstract：
In North China, iodine-rich groundwater has been extensively studied, but few in South China. This study aimed to investigate the characteristics of iodine-rich groundwater in South China and identify potential contamination sources. The results revealed that the average concentration of iodine in groundwater was 890 µg/L, with a maximum concentration of 6350 µg/L, exceeding the permitted levels recommended by the World Health Organization (5-300 µg/L). Notably, the enrichment of iodide occurred in acidic conditions (pH = 6.6) and a relatively low Eh environment (Eh = 198.4 mV). Pearson correlation and cluster analyses suggested that the enrichment of iodide could be attributed to the intensified redox process involving Mn(II), iodine (I2), or iodate (IO3-) in the soil. The strong affinity between Mn(II) and I2/IO3- facilitated their interaction, resulting in the formation and mobilization of I- from the soil to the groundwater. Leaching experiments further confirmed that reducing substances (such as sodium sulfides, ascorbic acids, and fulvic acids) in the soil with low dissolved oxygen (DO) levels (< 1.0 mg/L) enhanced the dissolution of iodine species. Conversely, higher DO content (> 3.8 mg/L) promoted the oxidation of I- into I2 or IO3-, leading to its stabilization. This research provides new insights into the characteristics and mechanisms of I- enrichment in groundwater in South China, and emphasizes the significance of the redox reactions involving Mn(II) and I2/IO3-, as well as the influence of soil properties in regulating the occurrence and transportation of iodine species within groundwater systems.
摘要：
在中国北方,富含碘的地下水已经被广泛研究，但在中国南方很少。本研究旨在调查中国南方富碘地下水的特征，并确定潜在的污染源。结果表明，地下水中碘的平均浓度为890µg/L，最大浓度为6350µg/L，超过世界卫生组织建议的允许水平（5-300µg/L）。值得注意的是,碘化物的富集发生在酸性条件（pH=6.6）和相对较低的Eh环境（Eh=198.4mV）。Pearson相关性和聚类分析表明，碘化物的富集可能归因于涉及Mn（II）的强化氧化还原过程，碘（I2），或土壤中的碘酸盐(IO3-)。Mn（II）和I2/IO3-之间的强亲和力促进了它们的相互作用，导致I-从土壤到地下水的形成和动员。浸出实验进一步证实了还原性物质(如硫化钠、抗坏血酸,和富里酸）在溶解氧（DO）水平较低（<1.0mg/L）的土壤中增加了碘物种的溶解。相反，较高的DO含量（>3.8mg/L）促进了I-氧化为I2或IO3-，导致其稳定。该研究为中国南方地下水中I-富集的特征和机制提供了新的见解。并强调了涉及Mn（II）和I2/IO3-的氧化还原反应的重要性，以及土壤特性在调节地下水系统中碘物种的发生和运输方面的影响。
