Uptake and transformation of per- and polyfluoroalkyl substances from aqueous film-forming foams in concrete
Notice bibliographique
Résumé
The significant environmental occurrence of per- and polyfluoroalkyl substances (PFAS)due to their ubiquity in many consumer and industrial products combined with their potentiallyharmful health effects has caused increased attention from regulators in recent years. Asignificant source of PFAS contamination is the utilization of aqueous film-forming foams(AFFF) in combatting class B fires at airports, military bases, and firefighter training facilities.Extensive research has investigated PFAS contamination across solid and aqueous matrices,encompassing surface water, wastewater, groundwater, biosolids, and soils. Contamination ofconcrete – an often-overlooked matrix and potential PFAS source – remains underexplored,particularly at military bases and airports. As a ubiquitous construction material globally,concrete is directly exposed to AFFF during training exercises, particularly in the form of groundslabs at impacted sites. Limited studies examining concrete from these sites have revealedsubstantial PFAS presence stemming from both electrochemical fluorination (ECF)-based andfluorotelomer (FT)-based AFFFs, highlighting concrete's potential for long-term PFAS leachingeven years after AFFF activities have ceased. Numerous questions persist regarding AFFFcontamination of concrete, including diffusion rates, the influence of AFFF additives, andconcrete-PFAS chemical interactions, warranting further investigation. This thesis aims tounderstand the physicochemical interactions between concrete and AFFF under conditionsmimicking those at impacted sites to better understand the ultimate fate of PFAS upon initialexposure to concrete in the environment.First, laboratory-based experiments were conducted to assess the artificial PFAScontamination of concrete using individual PFAS and ECF AFFF. Evaluation of PFAS uptake inconcrete encompassed flat finished surfaces and chipped surfaces to simulate aged concretevariability. Additionally, various PFAS within an AFFF mix, including dominantperfluorosulfonic acids (PFSAs) and precursors, were examined using high-resolution massspectrometry. Analysis of PFAS and AFFF solutions pooled onto concrete surfaces revealed nosignificant concentration decrease, while examination of powder from lab-contaminated coresindicated PFAS diffusion primarily within the top 0.5 cm of the core, with faster penetrationobserved in chipped surface concrete compared to flat surface. The contradiction was becausePFAS mass in concrete cores only represented a small fraction (1.3% to 10.8%, mean 3.9%) ofinitial spiked PFAS. A correlation between decreasing PFAS chain length and increased mobilityor diffusivity through cores was evident, suggesting that AFFF additives influence PFASdiffusion in concrete. Furthermore, intermittent wetting and drying cycles accelerated PFASpenetration, albeit equally for PFAS of differing chain lengths, probably due to the wickingeffect. Cores from a Canadian military base contained a mix of ECF and FT PFAS, with 6:2fluorotelomer sulfonate (6:2 FTSA) being most abundant in the top 1 cm of the core, withperfluoroctanesulfonic acid (PFOS) being dominant throughout the rest of the core suggesting arecent switch from ECF to FT foams.A comprehensive extraction method for PFAS from AFFF-affected concrete, validatedthrough spike-recovery trials, was also developed in this work. Seven solvent conditions wereassessed for their efficiency in extracting perfluoroalkyl acids (PFAAs) and 14 distinct precursorclasses present in ECF-based AFFF-contaminated concrete powder. Methanol with 100 mMammonium acetate was the optimal solvent for extracting a broad spectrum of anionic, cationic,and zwitterionic compounds, although other solvent conditions exhibited comparable recoveryrates for most PFAS. Recovery analysis of perfluorocarboxylic acids (PFCAs), perfluoroalkylsulfonamides (FASAs), and perfluoroalkyl amido amines (PFAAAm) compounds indicated highrecoveries for PFCAs and FASAs, contrasting with notably low recoveries for PFAAAmcompounds, implying rapid degradation of amide-containing precursors during extraction. Thisdegradation mechanism was attributed to alkaline hydrolysis facilitated by calcium hydroxideleaching from concrete. Additionally, investigations into sulfonamide precursors suggestedsalting-out effects rather than compound degradation as the primary cause for their rapidconcentration decrease.This work provides important findings on the kinetics of uptake of PFAS into concretefrom AFFF, as well as potential transformations that can occur at concrete-water interfaces,within concrete, and during extraction
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».