PFAS adsorption to air-water interfaces: Effects of velocity and PFAS concentration
Bibliographic record
Abstract
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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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| 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".