Per- and Polyfluoroalkyl Substances in Contaminated Soil and Groundwater at Airports: A Canadian Case Study

The
occurrence of 93 classes of per- and polyfluoroalkyl substances
(PFASs) was investigated at aqueous film-forming foam (AFFF)-impacted
sites of four Canadian airports. Surface/subsurface soil and groundwater
samples were characterized using high-resolution mass spectrometry
(HRMS) and an improved total oxidizable precursor (TOP) assay. PFAS
profiles, loads, and spatial trends were highly site-specific, influenced
by the AFFF use history, variations in sorption, transport, and in situ transformation potential of PFASs. All sites have
been impacted by more than one AFFF chemistry, with the active firefighter
training area exhibiting a greater PFAS variety and total PFAS burden
than decommissioned sites. Zwitterionic and cationic compounds composed
a large percentage (34.5–85.5%) of the total PFAS mass in most
surface soil samples in the source zone but a relatively low percentage
(<20%) in groundwater samples. Background soils surrounding the
source zone contained predominantly unidentified precursors attributed
to atmospheric deposition, while in AFFF-impacted soils, precursors
originating from AFFFs can be largely captured by HRMS using available
suspect lists. Horizontal transfer of PFASs in surface soils was limited,
but vertical migration down the soil column occurred even in locations
of low permeability. This study provides a critical data set to support
developing new priority analyte lists and integrating TOP assay for
comprehensive PFAS monitoring at AFFF-impacted sites.