Elevated PFAS Precursors in Septage and Residential Pump Stations.

Residential wastewater, with no industrial inputs, is an underrecognized source of per- and polyfluoroalkyl substances (PFAS). This study provides the first direct comparison of PFAS in septage and pump stations, targeting 70 PFAS compounds and employing the total oxidizable precursor (TOP) assay. Septage exhibited markedly higher PFAS and precursors concentrations than pump stations, with median post-TOP levels of 687.5 ng/L vs 84.2 ng/L, respectively. FTCAs were fully oxidized, while diPAPs showed incomplete oxidation due to high organic loads. Septic systems function as PFAS reservoirs, increasing risks of groundwater contamination, particularly in areas with shallow aquifers. Pump stations contributed to episodic PFAS spikes, likely affecting downstream wastewater treatment. The detection of 27 PFAS compounds, including short-chain alternatives, highlights shifting contamination patterns. Findings emphasize the need for tailored analytical frameworks and pretreatment technologies to mitigate PFAS risks across decentralized and centralized wastewater systems. Integrating precursor analysis is critical for accurate risk assessment, as targeted PFAS measurements underestimate contamination. These results provide new insights into PFAS behavior in residential wastewater, guiding future mitigation efforts.