Investigation of Environmental Fate of Novel Perfluoroalkyl and Polyfluoroalkyl Substances in Soil and Biosolids
Bibliographic record
Abstract
Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have received great attention due to their ubiquitous detection in the environment. As PFASs are among the most persistent organic compounds, and some are toxic and bioaccumulative, it is important to understand concentrations, sources, and environmental fate of PFASs in different environmental matrices. To shed light on the sources and behaviours of PFASs observed in soil, this thesis focused on (1) evaluating biotransformation in aerobic soil of fluorotelomer phosphoric esters (PAPs), and (2) assessing the levels of identifiable and unidentified PFASs in municipal biosolids intended for land application. In the first part of the thesis, biotransformation rates of two major PAPs (6:2 and 8:2 diPAPs) were evaluated in a semi-dynamic system over 112 days. Soil samples were prepared using an improved sample extraction preparation method, which has demonstrated the best recoveries for the diPAPs and the least propensity to cause undesirable solvent-enhanced hydrolysis. At the end of 112 days, the major polyfluoroalkyl carboxylic acids that were formed from 6:2 diPAPs were 9.34% 5:3 polyfluoroalkyl acid (5:3 acid), 6.42% perfluoropentanoic acid (PFPeA) and 5.99% perfluorohexanoic acid (PFHxA); the major one formed from 8:2 diPAPs was 2.14% perfluorooctanoic acid (PFOA). The half-lives of 6:2 diPAP and 8:2 diPAP were estimated to be 11.5 days and >1000 days, respectively. The approximate linear relationship between the half-lives of eleven PFASs (including 6:2 and 8:2 diPAPs) and their molecular weights suggested that the molecular weight is a good indicator of the general stability of low-molecular-weight PFAS-based compounds. In the second part of the thesis, 12 municipal biosolid samples were collected in Canada. Concentrations of 28 PFASs, including 13 perfluoroalkyl carboxylic acids (PFCAs, C4-C14, 5:3 and 7:3 acids), 4 perfluoroalkyl sulfonic acids (C4, C6, C8, and C10), 4 fluorotelomer alcohols (8:2 FTOH, 6:2 FTOH, 7:2 sFTOH and 5:2 sFTOH), 3 fluorotelomer sulfonic acids (8:2 FTS, 6:2 FTS and 4:2 FTS), and 4 PAPs (8:2 diPAP, 6:2 diPAP, 8:2 monoPAP, and 6:2 monoPAP), were determined. The predominant PFASs in most of the samples were perfluorobutane sulfonic acid (PFBS), 5:3 acid, 6:2 diPAP, 8:2 FTOH and 6:2 FTOH, but not PFCAs or perfluorooctane sulfonic acid (PFOS). The significantly different PFAS profiles from those in the U.S. biosolids suggested the use of different PFAS products in Canada. A persulfate oxidation based assay was applied to determine the level of unidentified PFASs in biosolids. Further studies are needed to optimize the assay to determine whether the approach is feasible for biosolid samples. This study has contributed to a deeper understanding of environmental fate and potential sources of selected PFAS species in soil environment.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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".