Source Elucidation of Perfluorinated Carboxylic Acids in Remote Alpine Lake Sediment Cores
Bibliographic record
Abstract
Atmospheric deposition of perfluorinated carboxylic acids (PFCAs) in remote regions might arise from transport and degradation of precursors (e.g., perfluorooctanesulfonyl fluoride (PFOSF)-based products or fluorotelomer alcohols (FTOHs)) or direct transport (e.g., PFCAs in the vapor phase or on particles). To probe the dominant atmospheric source of PFCAs, historical trends in environmental FTOH, PFOSF, and direct perfluorooctanoate (PFOA) emissions were compared to the flux of PFCAs (sum of C7-C13 perfluoroalkyl chain lengths) and PFCA isomer signatures in dated sediment cores from two remote alpine lakes in the Canadian Rocky Mountains. Contributions from PFOSF-based substances and direct transport of PFOA were ruled to be minimal because no branched isomers were detected in either core and temporal trends for direct emission of PFOA did not match the flux measurements. PFCA flux to Lake Opabin sediment agreed well with reported FTOH emissions, including a peak in mid-2003 and subsequent decline. In Lake Oesa, agreement between PFCA flux and FTOH emissions was also good up to 2004, but a subsequent decline was only detected for some PFCA congeners through 2008, while others continued to increase. Overall, both the isomer profiles and the temporal trend data suggest that FTOH oxidation is the dominant atmospheric source of PFCAs to these high alpine lakes. The efficacy of recent industry phase-out initiatives was difficult to assess due to the divergent temporal trends in samples after 2003; thus, continued monitoring is suggested at remote sites such as these.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.000 | 0.004 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 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 teacher head, 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".