PFAS adsorption to air-water interfaces: Effects of velocity and PFAS concentration
Notice bibliographique
Résumé
Understanding how per- and poly-fluoroalkyl substances (PFAS) are transported in soil and groundwater is critical to site characterization, monitoring, risk assessment, and remediation planning. This includes an understanding of PFAS retention and release associated with adsorption to air-water interfaces, which is particularly important for transport through the vadose zone. Many previous laboratory studies have focused on individual PFAS with experiments conducted over a narrow range of concentrations and pore-water velocities. However, the effects of PFAS mixtures, concentrations and velocities are important to extend our understanding, and the application of numerical models, to realistic site conditions.In this study, a series of laboratory experiments was conducted using one-dimensional sand-packed columns (40 cm × 5 cm dia.). Trapped air bubbles were emplaced in the sand (quasi-saturated conditions) by sequential drainage and imbibition. Similar to fluctuations in the water table, this emplacement technique was used to create immobile air-water interfaces that are uniformly distributed throughout the column and are readily accessible to flowing water. Each experiment included separate injections of non-reactive tracer (NaCl) and PFAS solutions through both water-saturated and quasi-saturated columns. A clean, low organic carbon sand was used to eliminate solid-phase sorption (verified through comparison of non-reactive tracer and PFAS breakthrough in the water-saturated columns) and to isolate the effect of air-water interfaces. Experiments were conducted using single-component solutions of PFOS over a range of concentrations (2 to 1000 μg/L) and pore-water velocities (0.8 to 2.6 cm/day). Experiments were also conducted using diluted aqueous film-forming foam (AFFF) solutions containing PFOS. The results showed that PFOS breakthrough was significantly delayed in the presence of trapped air bubbles, and that breakthrough varied considerably with concentration and velocity. Greater retardation occurred generally at lower PFAS concentrations and slower velocities. However, the change in retardation due to a change in velocity was sensitive to concentration, with greater changes occurring for lower concentrations. PFOS breakthrough was also affected by the presence of other PFAS and surface active components in AFFF, with PFOS in the diluted AFFF arriving earlier than expected for an equivalent concentration of PFOS alone. Mixture effects were also observed in the breakthrough of other PFAS in AFFF, particularly concentration overshoot (effluent concentration temporarily greater than the influent concentration) of some less surface active PFAS. The results highlight the need for more comprehensive models of PFAS transport that incorporate non-ideal and competitive behaviour to capture processes occurring in complex field scenarios.
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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 | 0,001 |
| 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 | 0,000 |
| 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 ».