State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China.
Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China; Sino-Danish College of University of Chinese Academy of Sciences, Beijing, 101408, China; Sino-Danish Centre for Education and Research, Beijing, 101408, China.
Environ Pollut. 2022 Jun 1;302:119052. doi: 10.1016/j.envpol.2022.119052. Epub 2022 Feb 25.
Nitrate (NO) pollution in water bodies has received widespread attention, but studies on nitrogen transformation and pollution risk assessment are still limited, especially in rare earth mining areas. In this study, surface and groundwater samples were collected from the largest rare earth mining site in southern China, and analyzed for the hydrochemical and stable isotopic characteristics. The results showed that the NO concentrations ranged from 1.61 to 453.11 mg/L, with 35% of surface water and 53.3% of groundwater samples exceeding the WHO standard (i.e., 50 mg/L). Health risk assessment showed that 31.4% of the water samples had a moderate to high non-carcinogenic risk, and the high-risk areas were concentrated in rare earth mining regions. Additionally, adults were more vulnerable to the non-carcinogenic health risks than children. The high variability of δN-NO (from -6.43 to 17.09‰) and δO-NO (from -7.91 to 22.79‰) showed that NO was influenced by multiple nitrogen sources and transformation processes. Hydrochemistry and isotopic evidence further indicated that NO was primarily influenced by nitrification and hydraulic connection between surface and groundwater. The results of the Bayesian mixing model showed that about 70% of NO originated from mine drainage and soil N in the rare earth mining area, while more than 90% of NO originated from fertilizer, soil N, and manure and sewage in rural and urban areas in the middle and downstream. This study suggests reducing anthropogenic nitrogen discharge (e.g., leaching agents and fertilizer inputs) as the primary means of NO pollution control with biogeochemical processes (e.g., denitrification) to further reduce its pollution.
水体中的硝酸盐（NO）污染受到了广泛关注，但有关氮转化和污染风险评估的研究仍然有限，特别是在稀土矿区。本研究采集了中国南方最大的稀土矿区的地表水和地下水样品，分析了其水化学和稳定同位素特征。结果表明，NO 浓度范围为 1.61-453.11mg/L，35%的地表水和 53.3%的地下水样品超过了世界卫生组织（WHO）标准（即 50mg/L）。健康风险评估显示，31.4%的水样存在中至高非致癌风险，高风险区集中在稀土矿区。此外，成年人比儿童更容易受到非致癌健康风险的影响。δN-NO（-6.43 至 17.09‰）和 δO-NO（-7.91 至 22.79‰）的高变异性表明，NO 受到多种氮源和转化过程的影响。水化学和同位素证据进一步表明，NO 主要受硝化作用和地表水与地下水水力联系的影响。贝叶斯混合模型的结果表明，大约 70%的 NO 来源于稀土矿区的矿山排水和土壤氮，而 90%以上的 NO 来源于农村和城市地区的肥料、土壤氮、粪肥和污水。本研究建议减少人为氮排放（如浸出剂和肥料投入）作为控制 NO 污染的主要手段，同时利用生物地球化学过程（如反硝化作用）进一步降低其污染。
