Yang Chang, Chen Si, Dong Jianhui, Zhang Yunhui, Wang Yangshuang, Kang Wulue, Zhang Xingjun, Liang Yuanyi, Fu Dunkai, Yan Yuting, Yang Shiming
Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China.
Chongqing Huadi Resources Environment Technology Co., Ltd., Chongqing 401120, China.
Toxics. 2025 Jun 19;13(6):516. doi: 10.3390/toxics13060516.
Groundwater nitrate (NO) contamination has emerged as a critical global environmental issue, posing serious human health risks. This study systematically investigated the hydrochemical processes, sources of NO pollution, the impact of land use on NO pollution, and drinking water safety in an urban area of southwestern China. Thirty-one groundwater samples were collected and analyzed for major hydrochemical parameters and dual isotopic composition of NO (δN-NO and δO-NO). The groundwater samples were characterized by neutral to slightly alkaline nature, and were dominated by the Ca-HCO type. Hydrochemical analysis revealed that water-rock interactions, including carbonate dissolution, silicate weathering, and cation exchange, were the primary natural processes controlling hydrochemistry. Additionally, anthropogenic influences have significantly altered NO concentration. A total of 19.35% of the samples exceeded the Chinese guideline limit of 20 mg/L for NO. Isotopic evidence suggested that primary sources of NO in groundwater include NH-based fertilizer, soil organic nitrogen, sewage, and manure. Spatial distribution maps indicated that the spatial distribution of NO concentration correlated strongly with land use types. Elevated NO levels were observed in areas dominated by agriculture and artificial surfaces, while lower concentrations were associated with grass-covered ridge areas. The unabsorbed NH from nitrogen fertilizer entered groundwater along with precipitation and irrigation water infiltration. The direct discharge of domestic sewage and improper disposal of livestock manure contributed substantially to NO pollution. The nitrogen fixation capacity of the grassland ecosystem led to a relatively low NO concentration in the ridge region. Despite elevated NO and F concentrations, the entropy weighted water quality index (EWQI) indicated that all groundwater samples were suitable for drinking. This study provides valuable insights into NO source identification and hydrochemical processes across varying land-use types.
地下水硝酸盐（NO）污染已成为一个关键的全球环境问题，对人类健康构成严重风险。本研究系统调查了中国西南部某市区的水化学过程、NO污染来源、土地利用对NO污染的影响以及饮用水安全。采集了31个地下水样本，分析了主要水化学参数和NO的双重同位素组成（δN-NO和δO-NO）。地下水样本的特征是中性至微碱性，主要为Ca-HCO型。水化学分析表明，包括碳酸盐溶解、硅酸盐风化和阳离子交换在内的水岩相互作用是控制水化学的主要自然过程。此外，人为影响显著改变了NO浓度。共有19.35%的样本超过了中国规定的NO 20 mg/L的限值。同位素证据表明，地下水中NO的主要来源包括铵基肥料、土壤有机氮、污水和粪肥。空间分布图表明，NO浓度的空间分布与土地利用类型密切相关。在以农业和人工表面为主的区域观察到NO水平升高，而较低浓度与草地覆盖的山脊区域相关。氮肥中未被吸收的铵随降水和灌溉水入渗进入地下水。生活污水的直接排放和畜禽粪便的不当处置对NO污染有很大贡献。草地生态系统的固氮能力导致山脊地区的NO浓度相对较低。尽管NO和氟浓度升高，但熵权水质指数（EWQI）表明所有地下水样本都适合饮用。本研究为不同土地利用类型下的NO源识别和水化学过程提供了有价值的见解。
