Occurrence and environmental fate of per- and polyfluoroalkyl substances (PFASs) at aqueous film-forming foams (AFFF)-impacted sites
Bibliographic record
Abstract
Over the years, people have recognized that widely used per- and polyfluoroalkyl substances (PFAS) in industry and consumer products often appear as anthropogenic pollutants in the environment and biota. PFAS-containing aqueous film-forming forms (AFFFs) used for controlling class B fires constitute significant sources of PFAS pollution. The persistent, bioaccumulative and toxic properties of select PFAS call for a better understanding of the large chemical class in terms of their environmental behaviors and impact. In addition to anionic perfluoroalkyl acids (PFAAs), zwitterionic and cationic PFAS have been recognized as important constituents in AFFFs and at AFFF-impacted sites. However, assessing the environmental impact of AFFF deployment is challenging due to the large variety of PFAS species and complex chemistry. In particular, information on the appearance and abundance of zwitterionic and cationic PFAS is sparse, and the environmental behaviors of such compounds remain poorly understood. This thesis intends to fill such knowledge gaps.First, the PFAS profiles at four Canadian airports were characterized using a range of advanced analytical tools, which was the first study of its kind in Canada. Results showed that these airports were commonly impacted by more than one AFFF chemistry, while distinct PFAS profiles and loads indicate the influence of AFFF use history. In source zone areas, zwitterions and cations made a high contribution (34.5-85.5%) in surface soils but a low contribution (<20%) in groundwaters. The PFAS in source zone soils had limited horizontal transfer, while the vertical migration down soil columns occurred even in locations of low permeability. In the background soils where AFFF impact was insignificant, unidentified precursors made up high percentages, probably resulting from atmospheric deposition. The study provides improved methodology, new knowledge and a priority list of PFAS to support future PFAS monitoring and remediation efforts.Next, the biotransformation potential of zwitterionic polyfluoroalkyl compounds made via the historical electrochemical fluorination (ECF) process was investigated in aerobic soils. Two compounds with betaine head groups and two with tertiary amine groups were examined for the first time. The perfluoroalkyl sulfonamide betaine and tertiary amine were confirmed to be the precursors to perfluorooctane sulfonate (PFOS), while the amide betaine and tertiary amine were precursors to perfluorooctane carboxylate (PFOA). Comparing their transformation kinetics with four other previously reported ECF-zwitterions and cations indicates the great influence of structure, especially the nitrogen head groups, on the chemical persistence. Specifically, i) the ECF precursors with sulfonamide group have higher microbial stability than those with an amide group; ii) the ECF precursors containing quaternary ammonium or betaine groups have high stability in soils with DT50 in years or decades, while those with tertiary amine or amine oxide groups were less stable with DT50 of weeks or months. For the first time, this study establishes a preliminary structure-degradability relationship for ECF precursors
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".