Bibliographic record
Abstract
This thesis explores the fate of chiral compounds in the environment, with a focus on the utility of enantiomer measurements for elucidating pollutant sources. The enantiomer distributions of several chiral polychlorinated biphenyls (PCBs) were measured in the water column of the Hudson River Estuary, and the atmosphere above it, to provide evidence for the relative contribution of fresh versus historical sources. Racemic distributions were observed in air for all chiral congeners detected, but nonracemic distributions for PCB 95 occurred throughout the water column. The results suggest that the source of this congener, and potentially other congeners, to the local aquatic food web is weathered historical contamination. In contrast, the source of PCBs to the local atmosphere is likely fresh releases from the surrounding dense urban centre. The choice of peak integration technique and its effect on the measurement of chiral contaminants was studied. The common valley drop method was shown to bias calculated enantiomer fractions to a greater extent than a deconvolution method. Typical biases when using the valley drop method were shown to have a dramatic effect on environmental calculations that employ the enantiomer fraction. The enantiomer distributions and concentrations of PCBs in soil and air were determined in the region surrounding a hazardous waste incinerator in Alberta, Canada. Concentrations and homologue patterns showed that the incinerator was the primary source of PCBs to the region. Enantiomer distributions in air were largely racemic, yet nonracemic signatures were observed in soil. This data suggests that atmospheric PCBs in the region likely originate from recent emissions from the incinerator, and not revolatilization of historically deposited contaminants from soil. By examining concentrations, as well as isomer and enantiomer distributions of perfluorooctane sulfonate (PFOS) in several aquatic species, the impact of precursor compounds on concentrations of PFOS in the aquatic food web of Lake Ontario was deduced. Racemic distributions were observed in some forage fish, but nonracemic distributions were observed in invertebrate species as well as lake trout. Since the biotransformation of precursors to PFOS is known to be enantioselective, the observed nonracemic signatures in some aquatic species points to an influence of precursors on the local aquatic organisms body burdens of PFOS.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".