Persistent and Mobile Chemicals, Including Ultrashort-Chain PFAS, in Groundwater: Distribution, Relevant Factors, and...

Persistent and mobile (PM) chemicals, including ultrashort-chain per- and polyfluoroalkyl substances (PFAS), are continuously discharged into the water cycle, and many of them are poorly removed because of high polarity and recalcitrance. Their occurrence in groundwater, an important drinking water resource, remains underexplored. We investigated 180 PM chemicals in 82 groundwater samples across Saxony, Germany, using freeze-drying and supercritical fluid chromatography-high-resolution mass spectrometry (SFC-HRMS). 163 PM chemicals were determined, including pesticides, pharmaceuticals, PFAS, other industrial chemicals, and transformation products; concentrations of 72 compounds are reported in groundwater for the first time; 57 chemicals exhibited detection frequencies >50%. The median total PM chemical concentration was 23 μg L^-1, with pesticides (0.77 μg L^-1) and pharmaceuticals (0.69 μg L^-1) of similar totals and industrial chemicals being much higher (19 μg L^-1). Trifluoroacetic acid was the dominant single compound (median of 3.0 μg L^-1, n = 81). Median concentrations of single chemicals correlated with physicochemical properties (water solubility, lipophilicity, etc.). Site-specific factors (nitrate, dissolved organic carbon, depth) were also associated with PM chemical levels. Chemical co-occurrence revealed benzothiazole and N,N-dimethylformamide as indicators of higher overall PM chemical concentrations. Risk prioritization identified 33 priority chemicals, highlighting chloridazon-desphenyl and N-methylpiperidine as potential indicators of higher overall PM chemical risk. These findings clarify PM chemical behavior in groundwater and support refined monitoring strategies.