A new perspective: the application of element-specific isotopes in elucidating the environmental behavior of emerging contaminants

While stable isotope techniques (e.g., δ13C and δ2H) are valuable for understanding the environmental behavior of emerging contaminants (ECs), such as microplastics (MPs) and per- and polyfluoroalkyl substances (PFAS), their application can be constrained by the ubiquitous presence of these target elements in the vast majority of ECs. This study proposes two innovative strategies to address the existing challenges in elucidating MP and PFAS behaviors. First, we introduce the rhenium-osmium (Re-Os) isotope system as a novel tool for tracing MPs. Considering the petrogenic origin of plastics and the enrichment of Re-Os in crude oils, we hypothesize that plastic products may inherit source-specific Re-Os signatures. This hypothesis was supported by the chalcophile nature (strong affinity for sulfur) and organophilicity of Re-Os, as well as their thermal stability under industrial processing conditions. Second, for PFAS, we highlight the potential of position-specific carbon isotope analysis using nuclear magnetic resonance (NMR). The intramolecular carbon isotope variations driven by the strong C-F bond in PFAS could yield critical insights into their degradation mechanisms and pathways when analyzed via position-specific isotope analysis (PSIA) with NMR. Our findings highlight that both the Re-Os system and PSIA, though underutilized, are powerful tools. They hold significant potential to advance the tracing and fate assessment of these persistent contaminants.