Anthropogenic Gadolinium Accumulation and Rare Earth Element Anomalies of the Typical Urban River, North China: Evidence from the Three-Dimensional Tracing System

Anthropogenic rare earth elements (REEs), especially gadolinium, have emerged as microcontaminants in urban rivers. Therefore, understanding the sources of anthropogenic REEs in urban regions has been the focus of current studies. Here, we present the dissolved REE characteristics of a typical urban river in a megacity region during the wet season. The contents of total REE (∑REE) varied from 2.84–89.49 ng L–1, and heavy REEs were enriched relative to light REEs (LREEs). Furthermore, a buffer zone within 3 km was established along the river to avoid the influence of upper land use variations on lower reach measurements and also to identify the origins of anthropogenic REEs via the relationships between land use proportions and REEs. Pronouncedly positive Gd anomalies of 1.41–51.22 in all river samples were revealed by normalization via the Post-Archean Australian Shale (PAAS). A three-dimensional (3D) tracing system was set up among anthropogenic Gd (Gdanth) and two conventional ion ratios (NO3–/Na+, Cl–/Na+), which accurately obtained the impacts from the sewage treatment plant, industrial emissions, and urban sewage in the study region. Hence, more attention should be paid to the quantitative assessments of Gdanth in megacity rivers.