漳江口溶解态稀土元素的地球化学特征及影响因素

Geochemical Characteristics and Influencing Factors of Dissolved Rare Earth Elements in the Zhangjiang Estuary

河口区域稀土元素(Rare earth elements, REEs)的地球化学行为对理解海洋中REEs的循环具有重要意义。本文通过现场调查对2018年9月(暴雨时期)、2019年12月(旱季)及2020年8月(湿季)溶解态REEs在漳江口的分布特征、REEs的主要影响因素及人为稀土元素钆(Gd)污染进行研究。结果表明:漳江口溶解态REEs在不同时期的分布及分异存在显著差异,溶解态REEs含量暴雨时期>旱季>湿季。暴雨时期溶解态REEs主要呈现轻/中稀土相对富集及Ce正异常现象,而旱季及湿季溶解态REEs主要呈现重稀土相对富集及Ce负异常现象,颗粒物-水作用是不同时期溶解态REEs含量及分异存在差异的主要原因。Gd在不同时期均呈现正异常,暴雨时期、旱季及湿季人为Gd占比分别为18%~29%、26%~69%及22%~60%,推测Gd污染可能受河口上游医院核磁共振造影剂使用的影响。以上研究表明暴雨导致的颗粒物释放对河口溶解态REEs具有显著的贡献,今后研究需要重视特殊事件(如暴雨)对河口溶解态REEs来源和收支的影响。漳江口上游的人口密度相比全国其他地区较低但存在较为严重的人为Gd污染,说明我国其他河口人为稀土污染及来源也应引起广泛的重视。

The geochemical behavior of rare earth elements(REEs)in the estuaries are of great significance for understanding the cycling of REEs in the ocean.In this study,the distribution characteristics of dissolved REEs in the Zhangjiang estuary,the main influencing factors of REEs and anthropogenic gadolinium(Gd)pollution were examined by field investigation in September 2018(flood period),December 2019(dry season),and August 2020(wet season).The results showed that the distribution of dissolved REEs and fractionation in the Zhangjiang estuary varied significantly during different sampling periods,with the dissolved REEs content in flood period>dry season>wet season.And the dissolved REEs in flood period showed relative enrichment of light/medium REEs and positive Ce anomalies,on contrary,the dissolved REEs in dry season and wet season showed relative enrichment of heavy REEs and negative Ce anomalies,particle-water interaction is the dominant reason to explain the differences of dissolved REEs during different periods.Gd showed positive anomalies during different periods,the proportion of anthropogenic Gd in flood period,dry season and wet season were 18%~29%,26%~69%,and 22%~60%,respectively.It is speculated that Gd contamination may be influenced by the use of MRI contrast agents in the hospitals from upper estuary.This study indicated that the release of particles during the flood period contributes significantly to the dissolved REEs in the estuary.In future studies,the effects of special events(such as flood)on the sources and budgets of dissolved REEs in estuaries should be addressed.In addition,the population in the upper reaches of the Zhangjiang estuary is low but there is relatively serious anthropogenic Gd pollution,suggesting that other estuaries in China should also attract widespread attention to anthropogenic REEs pollution and its sources.