PFAS, 6-PPD-Q, and microplastics in urban sewer overflows: co-occurrence and high-rate treatment assessment

Abstract This study investigates the co-occurrence and concentrations of emerging contaminants in urban sewer overflows. Combined sewer overflows (CSOs) contained total PFAS concentrations up to 320 ng/L (mean: 33.2 ng/L), with post-TOP assay analysis indicating significant contributions from precursor compounds. The tire wear product, 6-PPD-Q, acutely toxic to aquatic life, was detected in CSOs at concentrations up to 895 ng/L (mean: 242 ng/L), directly linked to urban runoff. Various microplastic polymers were also frequently found in both CSOs and sanitary sewer overflows (SSOs), underscoring widespread plastic pollution. High-rate treatment (HRT) systems employing chlorination (for CSOs) and UV disinfection (for SSOs) effectively reduced 6-PPD-Q concentrations, but showed limited PFAS removal, with evidence suggesting precursor transformation into more persistent forms during treatment. Only partial microplastic removal was observed in the SSO treatment scenario, indicating a need for more effective strategies employing biological or physicochemical treatment. These findings necessitate targeted removal technologies to protect aquatic ecosystems and provide valuable baseline data for urban water management.