Applications of Compound-Specific Isotope Analysis for Determining Persistent Organic Pollutant Origin, Transport and Transformation in the Aquatic Environment

Since the 2001 signing of the Stockholm Convention on Persistent Organic Pollutants (POPs), scientists globally have refined the methodologies for understanding these compounds. Given that POPs can enter and move freely between diverse environmental media, the challenge has been to unravel their complex histories and determine how their sources, paths, and transformations contribute to area contamination. Owing to their connective nature and elevated burdens, riverine and estuarine systems have become focal points for POP research. Meanwhile, compound-specific isotope analysis (CSIA) has emerged as a promising tool for identifying pollutants, distinguishing molecularly similar compounds, and tracing chemical behavior based on process-associated signatures. Focused on insights into remediation, this review summarizes an existing body of research at the intersection of aquatic ecosystem monitoring of POPs and CSIA, centering on three archetypal pollutants: polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and the pesticide ΣDDT. It is found that added CSIA parameters are invaluable for source apportioning area pollution and for tracking biotransformation through its ecosystems. Several natural remediation processes are found to be detectable uniquely via CSIA of tissue samples. Nonetheless, the method remains underutilized in aquatic systems and is applied disproportionately for different pollutants, patterns attributable to its expertise demands and reliance on preceding literature. To promote its use, future work is recommended to standardize CSIA laboratory protocols and to resolve the isotopic signatures left by natural processes.