A Cross-Class Review of Emerging Groundwater Contaminants: PFAS, Antibiotic Resistance Genes, and Microplastics in Environmental Behavior, Monitoring, and Risk Assessment

Emerging contaminants in groundwater pose growing challenges because chemical, genetic, and particulate pollutants are measured and interpreted through fundamentally different evidence chains. This critical review compares per- and polyfluoroalkyl substances (PFASs), antibiotic resistance genes (ARGs), and microplastics across sources, subsurface behavior, monitoring, source apportionment, exposure and risk-related interpretation, and management. Cross-class synthesis highlights that the dominant evidence bottleneck shifts along the assessment chain: for PFASs, uncertainty is concentrated mainly after chemical quantification, where precursors, unknown organofluorine, mixtures, and benchmark definitions limit interpretation; for ARGs, the critical gap lies between gene detection or abundance and transmission relevance, requiring host, mobile genetic element, mobility, and exposure evidence; and for microplastics, uncertainty begins at the measurement-definition stage because sampling volume, particle-size cutoff, and particle-number versus mass reporting determine the apparent exposure metric. Consequently, harmonization should be stage-specific rather than uniform across contaminant classes. The review distinguishes directly comparable evidence from evidence constrained by analytical boundaries and separates quantitative risk assessment from risk screening, hazard characterization, exposure characterization, and relative prioritization. A cross-class decision framework links data quality, source evidence, hydrogeological vulnerability, receptor exposure, uncertainty, and management response. The practical value of integration therefore lies not in ranking contaminant classes on a common risk scale, but in identifying the limiting evidence link that must be resolved before a defensible groundwater-management decision can be made.