A review on integrated isotopic and receptor model approaches for urban REE source appointment

With rapid urbanization and industrialization, pollution of rare earth elements (REEs) in air, soil, and water is increasing in urban areas. These critical high-tech elements are becoming more abundant in urban dust and other environmental settings. It is difficult to differentiate and quantify the sources of REE pollution, as natural and anthropogenic sources overlap. This work couples isotopic tracing techniques (Pb, Sr, and Nd isotopes) with receptor models (positive matrix factorization (PMF) and absolute principal component scores/multiple linear regression (APCS/MLR)) to obtain robust source apportionment of REEs in urban environments. Isotopic fingerprints, including Gd anomalies, have been shown to serve as powerful tracers for distinguishing vehicular emissions, industrial discharges, and soil erosion. Non-exhaust vehicular emissions, especially those from brake and tire wear, have been identified as the main sources of REE release into the environment. The combination of isotopic methods and receptor models enhances the accuracy of source apportionment and contributions, facilitating better environmental management. The review highlights the need for standardized isotope libraries and sophisticated modelling tools to characterize sources, thereby improving source apportionment and informing sustainable control strategies for urban pollution. Focusing on controlling industrial and vehicle emissions can be an effective strategy to reduce REE contamination levels and human exposure.