Land application of sewage sludge as a pathway for emerging contaminants: a comparative review of microplastics, PFAS, and pharmaceuticals.

Agricultural application of treated sewage sludge supports nutrient and organic matter recovery but can also transfer emerging contaminants retained in or associated with sludge during wastewater treatment to soil. This review evaluates microplastics (MPs), per- and polyfluoroalkyl substances (PFAS), and pharmaceutical residues across their sources, sludge association, treatment response, agricultural loading, environmental fate, exposure pathways, potential effects, and regulation. Evidence identified through targeted searches of the Web of Science Core Collection and Scopus was integrated using a structured narrative review and comparative qualitative synthesis. These groups share a sludge-to-soil pathway but exhibit fundamentally different environmental profiles. MPs are retained mainly through physical association with solids and remain environmentally relevant through persistence, fragmentation, and size-dependent redistribution. PFAS behavior reflects compound-specific partitioning, the high persistence of many perfluoroalkyl acids (PFAAs), precursor transformation, and the greater mobility of many shorter-chain PFAAs under some soil conditions. Pharmaceutical residues show compound-specific variation in sorption, degradation, transformation, mobility, biological activity, and plant uptake. Conventional sludge treatments often redistribute contaminants or modify measured profiles without establishing destructive removal. High-temperature thermal processes may achieve greater destruction of some contaminants under suitable operating conditions, but transformation-aware whole-process mass balances remain necessary. Existing European Union and US sludge frameworks remain centered largely on conventional pollutants, although PFAS-related assessment and management are developing. The comparison demonstrates that occurrence alone does not establish risk and that a single uniform monitoring or management framework is inadequate. Class-specific monitoring, treatment evaluation, and long-term field evidence are needed to support environmentally defensible land application.