Anthropogenic gadolinium as a tracer of urban impact in the Chinese Capital Economic Circle: Distribution, sources, and sustainable remediation perspectives.

As cities expand, anthropogenic gadolinium (Gdanth), mainly from medical contrast agents, is emerging as a significant pollutant in urban rivers. Rapid urbanization and rising medical wastewater discharge have accelerated the accumulation of REEs, particularly Gdanth, posing new ecological and health challenges. This study investigated two representative urban rivers in the Chinese Capital Economic Circle to elucidate how human activities shape REE behavior in megacity river, and the environmental factors driving these changes. By combining land use classification, buffer zone extraction, and Spearman correlation analysis, a strong positive correlation was revealed between urban land use proportion and Gdanth. By integrating Gdanth with NO3⁻/Na⁺ and Cl⁻/Na⁺, an innovative tracing system was developed to effectively trace pollution sources such as wastewater treatment plants, industrial facilities, hospitals, and farmland. To address this issue, this study proposes an innovative treatment strategy tailored for medical wastewater in megacities. The system conceptually integrates guava seeds as a sustainable carbon source, TiO2 as a photocatalyst, and hybrid membrane technology to synergistically enhance the removal of gadolinium-based contrasting agents (GBCAs) and coexisting contaminants. This conceptual approach provides a novel technical pathway and theoretical foundation for wastewater reuse, pollutant recovery, and sustainable environmental management in highly urbanized regions.