青藏高原冰川融水释放全氟烷基酸的时空特征:以扎日南木措和雀莫措流域为例[封面文章]

Spatial and temporal characteristics of perfluoroalkyl acids released from glacial meltwater on the Qinghai-Xizang Plateau: a case study of Zhari Nam Co and Quemo Co basins[Cover]

关键词:  青藏高原  全氟烷基酸  冰川融水  时空特征  水化学

Key words:  Qinghai-Xizang Plateau  perfluoroalkyl acids (PFAAs)  glacial meltwater  spatial and temporal characteristics  water chemistry

摘要:

气候变暖导致冰川持续消融，使其长期储存的污染物不断向下游环境释放。然而，不同水文来源冰川融水中全氟烷基酸 （PFAAs） 的变化特征仍缺乏认识。文章以青藏高原扎日南木措 （远离冰川末端的“旧水”）和雀莫措（靠近冰川末端的“新水”）流域为研究对象，于2021年4—6月（消融前期）和 8—10月（消融后期）采集43个冰川融水样品，分析了C₄—C₁₂全氟烷基羧酸（PFCAs）和C₄、C₆和C₈全氟烷基磺酸 （PFSAs） 共12种PFAAs的赋存和时空分布特征，并结合10项水化学参数探讨其影响因素。 结果表明，扎日南木措流域PFAAs浓度为732—4375 pg/L （平均浓度2086 pg/L），雀莫措流域为593— 7282 pg/L （平均浓度2026 pg/L），总体与全球其他偏远地区相当，处于较低污染水平。两流域融水均以 C₄—C₉ PFCAs和全氟丁烷磺酸 （PFBS） 为主要组分，但主导单体存在差异，扎日南木措以PFBS为主， 而雀莫措以全氟丁酸 （PFBA） 为主。与消融前期相比，消融后期两流域融水中短链PFCAs占比下降， 而PFBS占比明显增加，表明冰川融水持续冲刷河流沉积物和周边土壤可能促进储存于固相中的PFAAs 逐渐释放进入径流。空间上，两流域PFAAs浓度沿径流方向总体呈先升高后降低的趋势，反映径流传输及土壤侵蚀过程的影响。相关性和主成分分析表明，pH、水温及氟化物等水化学参数对PFAAs浓度变化具有重要影响，其中 pH 和氟化物是影响径流中 PFAAs 变化的主要因素。总体而言，靠近冰川末端的 “新水”中PFAAs主要受冰雪消融强度控制，而远离冰川的“旧水”则更多受水文传输及水化学过程影响。研究结果有助于认识青藏高原冰川融水中PFAAs的污染特征及其迁移机制，为高寒地区水生态环境保护提供科学依据。

Abstract:

Background, aim, and scope Climate warming has accelerated glacier retreat worldwide, leading to the release of contaminants historically stored in glaciers into downstream environments. Perfluoroalkyl acids (PFAAs) are persistent pollutants that have been widely detected in glacial regions, yet their variation characteristics in meltwater with different hydrological sources remain poorly understood. This study aims to investigate the occurrence, spatial distribution, and seasonal variation of PFAAs in glacial meltwater from two contrasting basins on the Qinghai-Xizang Plateau: the Zhari Nam Co basin representing “old water” far from glacier termini and the Quemo Co basin representing “new water” close to glacier termini. Materials and methods A total of 43 glacial meltwater samples were collected from the two basins during the pre-ablation period (April −June) and post-ablation period (August−October) in 2021. Twelve PFAAs, including C₄—C₁₂ perfluoroalkyl carboxylic acids (PFCAs) and C₄, C₆, and C₈ perfluoroalkyl sulfonic acids (PFSAs) were analyzed to determine their concentration levels and compositional characteristics. In addition, ten hydrochemical parameters, including water temperature, pH, dissolved oxygen (DO), electrical conductivity (EC), total nitrogen (TN), ammonia nitrogen (NH3-N), total phosphorus (TP), arsenic (As), fluoride (F− ), and chloride (Cl− ), were measured, and correlation analysis together with principal component analysis (PCA) was applied to identify the factors influencing PFAAs variations. Results Total PFAAs concentrations ranged from 732—4375 pg/L (mean: 2086 pg/L) in the Zhari Nam Co basin and 593—7282 pg/L (mean: 2026 pg/L) in the Quemo Co basin, which are comparable to those reported in other remote regions worldwide and indicate relatively low contamination levels. In both basins, C₄—C₉ PFCAs and perfluorobutane sulfonic acid (PFBS) were the dominant components, while the predominant compounds differed between basins: PFBS dominated in the Zhari Nam Co basin, whereas perfluorobutanoic acid (PFBA) dominated in the Quemo Co basin. Compared with the pre-ablation period, the proportions of short-chain PFCAs decreased, whereas PFBS increased during the post-ablation period. Spatially, PFAAs concentrations generally increased first and then decreased along the flow direction in both basins. Discussion The seasonal shift in PFAAs composition suggests that continuous flushing by glacial meltwater may enhance the gradual release of PFAAs stored in river sediments and surrounding soils into runoff. Hydrochemical conditions also played important roles in regulating PFAAs distribution. Among the measured parameters, pH and fluoride showed the strongest correlations with PFAAs concentrations, indicating that hydrochemical processes significantly influence the transport of PFAAs in glacial meltwater. Conclusions Overall, PFAAs in meltwater close to glacier termini (“new water”) were mainly controlled by glacier melt intensity, whereas those in downstream meltwater (“old water”) were more strongly influenced by hydrological transport processes and hydrochemical conditions. Recommendations and perspectives This study improves the understanding of contamination characteristics and transport mechanisms of PFAAs in glacial meltwater on the Qinghai-Xizang Plateau. Long-term monitoring and integrated hydrological-geochemical studies are recommended to better quantify pollutant release from retreating glaciers and evaluate their potential environmental risks in alpine ecosystems.