What we learn from using mass balance approach and oxidative conversion - A case study on PFAS contaminated soil...

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Soil Science

Background:

• Per- and polyfluoroalkyl substances (PFAS) are widespread synthetic chemicals with limited understanding of their full extent in contaminated environments.
• Existing analytical methods for PFAS in soil may underestimate total pollution due to limitations in detecting diverse PFAS compounds and precursors.
• Aqueous film-forming foam (AFFF) is a significant source of PFAS contamination in various soil matrices.

Purpose of the Study:

• To introduce and validate a comprehensive analytical workflow for assessing organofluorine in PFAS-contaminated soils.
• To compare the effectiveness of different analytical techniques, including total fluorine, extractable organofluorine, target PFAS analysis, and oxidative conversion, in characterizing PFAS pollution.
• To identify the limitations of current methods and propose an improved approach for accurate PFAS assessment in AFFF-impacted soils.

Main Methods:

• Development of a stepwise analytical workflow integrating total fluorine (TF), extractable organofluorine (EOF), target PFAS analysis, and PFAS precursor oxidative conversion.
• Application of the workflow to ten field soil samples from AFFF-contaminated sites.
• Quantification of target PFAS, assessment of EOF, and evaluation of organofluorine contributions from precursor conversion.

Main Results:

• Target PFAS concentrations varied widely (51.8–23200 ng/g dry weight), with perfluorooctanesulfonic acid being predominant.
• Target PFAS represented only a fraction (1–80%) of EOF, with oxidative conversion revealing additional contributions (0–31%).
• A significant portion (20–94%) of organofluorine remained unidentified, and oxidative conversion correlated better with EOF than target analysis, suggesting its utility for assessing the total organofluorine burden.

Conclusions:

• Total fluorine analysis is not suitable for tracing PFAS contamination in soils.
• A combination of oxidative conversion and routine PFAS target analysis provides a more comprehensive assessment of PFAS contamination in AFFF-impacted soils.
• Further research is needed to identify unknown organofluorine compounds and improve the understanding of non-oxidizable PFAS and ultra-short chain PFAS.