Research On The Distribution Characteristics Of Rare Earth Elements In The Surface Water System Of Shanghai And The Source Of Anthropogenic Gd

Rare earth elements(REEs)have become an emerging contaminant in urban rivers with the massive growth in the consumption of REEs in high-tech products and processes over the past decades.To investigate the concentrations of rare earth elements in urban rivers and quantify the anthropogenic Gd(a typical human-derived REE)contribution,26 River water samples were collected in Shanghai,a megacity of China.The results obtained showed that the concentrations of total dissolved REE(?REEs)ranged from 36.17 ng/L to 143.02ng/L;the heavy rare earth elements(HREEs)were more enriched than the light rare earth elements(LREEs).Through the Post-Archaean Australian Shale(PAAS)normalized REEs distribution patterns,different extents of the anomaly are observed for Eu and Sm in the distribution patterns of REEs in surface water.The positive Eu anomaly is mainly caused by the weathering and transportation of local geological conditions.The Sm anomaly has no obvious point source,and further investigation is needed to determine its source.Besides,all samples showed significant positive Gd anomalies,with the Gd _SN/Gd^*_SN ranged between 1.79 and34.32.The anthropogenic Gd contribution to total Gd(Gd _Anthr./Gd _Measured)was over 85%in 4samples,which are located in downtown Shanghai(HP-5)and downstream of wastewater treatment plants(WWTP).A possible reason for the anomaly has been assigned to the Gd-based Contrast Agents(GBCAs),which were generally derived from the contrast agents of magnetic resonance imaging(MRI).Based on the discharge rate and anthropogenic Gd concentrations,its flux is estimated to be 497 kg/yr.By comparing the published river data in the world,it is found that there is a positive correlation between the anthropogenic Gd content in surface water and the medical level in this region.With the progress of science and technology and the development of medical treatment,more and more anthropogenic rare earth elements(such as Gd)will be imported into the natural environment worldwide,which will increase the potential risk of the water environment.Therefore,it is necessary to further study their migration rules and final destination,including potential toxicity,and further study their impact on human health.