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

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.