Per- and Polyfluoroalkyl Substances and Total Organic Fluorine Ratios from Field-Collected Light Nonaqueous Phase...

Per- and polyfluoroalkyl substances (PFAS) and light nonaqueous phase liquid (LNAPL) co-occur in the subsurface at military installations. Concentrations of PFAS in 13 paired LNAPL and groundwater samples collected from groundwater wells were used to compute LNAPL:groundwater ratios (γ_LNAPL-GW). Individual target PFAS were determined by liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF) while total organic fluorine and fluoride were determined by ¹⁹F nuclear magnetic resonance spectroscopy (NMR). The percent aromatic content of LNAPL was determined using ¹³C NMR. The PFAS concentrations in LNAPL ranged from 80 ng/L to >5,000,000 ng/L. The summed molar concentration of individual PFAS accounted for up to 26.7% of total organic fluorine. Individual PFAS γ_LNAPL-GW values ranged from <1 to 557, while γ_LNAPL-GW for total organic fluorine ranged from 0.003 to 18.3. For a given LNAPL-groundwater sample pair, there was a headgroup and fluorinated chain length effect on γ_LNAPL-GW. Visualization of γ_LNAPL-GW across samples indicated that both PFAS structure and LNAPL and groundwater characteristics strongly influenced partitioning. Linear mixed-effects modeling indicated that environmental parameters accounted for 36.5% of the variance in γ_LNAPL-GW, increasing to 72.0% when PFAS class and chain length were included. Strong multicollinearity among variables limits the ability to identify singular dominant factors; thus, controlled laboratory studies are needed.