稳定碳同位素对富有机质地下水系统中碘迁移富集的指示研究

As one of countries first discovering thyroid diseases resulting from water sources problems, many residents in China are suffering from excessive iodine intake. In this study, inland Datong basin, as a typical case, will be selected to study the genesis of elevated iodine concentration in groundwater system. Given the evidently close relationship between organic matter and iodine, quantifying the cyclic processes of natural organic-iodine matter becomes the central to understand the iodine release and enrichment in groundwater. Therefore, an analysis technology of stable carbon isotope will be performed on groundwater and sediment samples to evaluate the mechanisms of carbon isotope fractionation and to further establish the local-scale degradation model for groundwater organic-iodine organic matter under a range of degradation rates. Moreover, some additional approaches, such as field monitoring, laboratory conditional experiments and hydrogeochemical processes modeling, will be conducted to quantitatively assess the contributions of organic-iodine matter degradation to the groundwater iodine enrichment. All the works mentioned above are ultimately to deeply reveal the genesis of natural high iodine groundwater. This study will introduce a new approach to portray the groundwater iodine hydrogeochemical behavior. More importantly, it will contribute to improve the water sources management for natural high iodine groundwater and reduce the health threat of intensive exposure under high iodine environment on human.

我国是最早发现水源性高碘致甲状腺肿的国家之一，大同盆地是典型内陆高碘地下水分布区，含水层中原生有机质是碘迁移富集的重要影响因素，有机质的降解循环过程及其对碘迁移富集贡献的定量识别是高碘地下水成因研究的关键和难点。本项申请将以大同盆地富有机质地下水系统为研究对象，稳定碳同位素为主要研究手段，分析富碘有机质降解碳同位素分馏程度及地球化学循环过程；然后结合室内条件实验模拟不同反应进程同位素分馏效应，构建富碘含水层中有机质碳降解循环模型；在此基础上，结合野外观测和反应速率模型，定量研究富碘有机质不同降解时间进程对水体中碘富集的贡献程度，丰富内陆盆地原生高碘地下水形成机理。本项申请有针对性地选择稳定碳同位素作为研究手段，为深入揭示地下水碘迁移富集的微观地球化学行为提供了新的研究思路，同时对减轻高碘暴露环境对人体健康造成的危害、保障地下水资源合理开发利用提供了科学决策依据，具有重要的现实意义。

近年，多地报道发生有原生高碘地下水，对当地居民饮水安全造成一定威胁，并认为对近年攀升的甲状腺癌变有一定影响。基于此，项目选取我国原生高碘地下水为研究对象，内陆大同盆地及沿海华北平原为代表性研究区，完成区域内地下水/沉积物样品采集工作，在完成样品基础理化性质表征之上，借助无机/有机碳同位素及固相同步辐射微观表征手段，深入探究地下水系统碘迁移释放富集机理，为后续高碘区饮水安全及治理提供科学理论依据。研究取得的主要认识如下：（1）提取利于碘富集的水环境因素：原生高碘地下水多发生于偏还原/弱氧化、偏碱性的水体环境条件，该水环境利于碘以活性更强的离子态赋存于其中，偏碱性环境中固相介质对碘离子的吸附能力较弱；（2）查明固相介质碘搭载载体：高碘地下水中碘的宏观来源为受海相及古湖相影响的沉积介质，微观搭载载体为结晶程度较高的铁矿物相及有机质；（3）识别固相碘释放并在液相发生富集的水文地球化学过程：在浅层及中深层地下水中均发现有高碘地下水，浅层水体受地表人为活动影响发生周期性氧化还原波动及外源物质输入，促使固相介质碘发生释放，深层地下水主要受长期地质时间尺度铁矿物相还原性溶解，造成固相碘释放并以碘离子的形式在液相中发生富集。研究内容围绕原生高碘地下水的形成机理，开展多水平、多层次系统性研究，室内实验及微观表征结果为其提供直接证据，基于此所提取的主控因素更为后续有针对性的开展高碘地下水的预测及治理提供基础科学理论依据。