Natural Radionuclides in Groundwater (NORM) (WMS)

Considering water as the primary resource necessary for social life, agriculture, industry, and wealth, the importance of groundwater investigation is clear. Apart from many other pollutants, this work focusses on geogenic uranium (U) and radium (Ra), which both stand for natural radionuclides (NORM) that need to be considered frame of groundwater exploration and monitoring programmes due to their specific mobility and chemo-/radiotoxicity. As investigation of U and – to a lesser extent - Ra is done by an increasing number of scientific working groups, the global dataset is improving continuously. In order to give a summarized overview on available and recent literature, scientific papers, reports, and governmental documents have been reviewed for U-238 mass concentrations and Ra-226 and Ra-228 activity concentrations and collected in tables and global maps. Further natural isotopes of U and Ra have been rarely subject of investigation. The collected data were evaluated and interpreted in frame of an associated scientific publication (see citation). From the available data it can be concluded that high geogenic U occur mainly under oxidizing conditions and carbonate rich groundwater, which might be seen as indicator for elevated U concentrations. Certain geological formations, as for example sedimentary, granitic, and volcanic host rocks, promote high U concentrations in groundwater. For geogenic Ra, the search for definite indications proved difficult, since less clear correlation is given for any observed factor. In a global perspective, the most promising evidence for elevated Ra are highly reducing redox conditions, as well as the occurrence of Fe/Mn mineral phases. Furthermore, barite represents a sink for Ra due to its ability to incorporate Ra isotopes. Dissolution of those mineral phases eventually results in co-dissolution of Ra, when Ra is found in host rocks of investigated aquifers, or downstream of such groundwater reservoirs. Furthermore, cation exchange might enhance Ra mobility process, especially in case of sedimentary aquifers with low sorption capacity and/or aquifers with high salinity. Given those chemical requirements for the occurrence of U and Ra, a negative correlation between mother and daughter nuclide can be established. When knowledge on present geological and geochemical constraints is available, elevated U and Ra concentrations might be predictable, as long as anthropogenic influence is excluded.水作为社会生活、农业、工业及经济发展必需的核心资源，地下水调查的重要性不言而喻。除诸多其他污染物外，本研究聚焦于成因铀（U）与镭（Ra）——二者均属于天然放射性核素（NORM），由于其独特的迁移性与化学/放射毒性，需纳入地下水勘探与监测方案的考量范畴。随着越来越多的科研团队开展铀（U）以及（在较小程度上）镭（Ra）的相关调查，全球数据集正持续完善。为系统梳理现有最新研究成果，本研究针对铀-238质量浓度、镭-226与镭-228活度浓度相关的文献、科研论文、报告及政府文件开展综述，并将相关数据整理为表格与全球分布图。铀与镭的其他天然同位素则鲜有成为调查对象。本数据集所收录的数据已在相关科研论文中完成评估与阐释（详见引用文献）。从现有数据可得出结论：高浓度成因铀主要赋存于氧化环境与富碳酸盐地下水中，这一特征可作为铀浓度升高的指示标志。特定地质建造——如沉积岩、花岗岩与火山岩赋矿围岩——会促进地下水中铀浓度升高。对于成因镭而言，明确其相关指示标志颇具难度，因为现有观测因素与镭浓度之间并未呈现清晰的相关性。从全球视角来看，镭浓度升高的最显著证据为强还原氧化还原环境，以及铁/锰矿物相的赋存。此外，重晶石可通过固载镭同位素成为镭的汇。当所研究含水层的赋矿围岩或此类地下水储库下游存在镭时，这些矿物相的溶解最终会导致镭的共溶出。此外，阳离子交换作用可能会增强镭的迁移能力，尤其是在吸附能力较低的沉积含水层和/或高盐度含水层中。基于上述铀与镭赋存的化学条件，可确立母核素与子核素之间的负相关关系。在排除人为影响的前提下，若掌握了相关地质与地球化学约束条件的相关知识，便可对铀与镭的浓度升高情况进行预测。