Chemical Fate of Photodegraded Diluted Bitumen in Seawater
Bibliographic record
Abstract
ABSTRACT2017-336: Diluted bitumen (dilbit), an oil sands product, may present new response challenges differing from conventional crude oil in terms of its potential environmental impacts. Simple naphthenic acids (NAs), a complex group of monocarboxylic acids, with a general formula CnH2n+zO2, may be present in the source bitumen or may be created by photolytic weathering. Knowing the composition and concentrations of NAs created during the photo-degradation process of dilbit will help understand the fate, behavior and toxicity of dilbit. In the present study, two diluted bitumen products, Cold Lake Blend (CLB) and Access Western Blend (AWB), were mixed with saltwater and irradiated with natural solar light (Ottawa, Canada, 45.4°N) over winter and summer seasons, to assess the impact of sunlight on the chemical fate of the dilbit. For comparison, a light, sweet crude oil was exposed under similar conditions. The samples were analyzed by high performance liquid chromatography-high resolution mass spectrometry to examine the molecular transformation of diluted bitumen by solar irradiation. The abundances of NAs in all three test oils increased significantly after 90 days of solar irradiation, strongly suggesting that polar NAs were formed by photolysis. Further, greater increases in NAs in the light crude were found than in the two dilbits. Similarly, the lighter oil had higher photolytic removal rates of petroleum hydrocarbons than the two dilbits. The concentrations of NAs in oils exposed during the summer were generally higher than those exposed in winter. During summer exposure, the abundance of total NAs increased up to the 30-day’s solar exposure, then fell again, indicating the transient nature of these compounds. However, net increases in polar NA compounds were observed for all the winter exposed samples. Greater increases were observed in the smaller NA compounds (average C-number decreased), also accompanied by an increase in saturation (average z-number decreased). These chemical changes strongly indicate the effect of sunlight on the potential behaviour, fate and effects of spilled oil, with creation of new resin group compounds and reduction of aromatics and saturates. These changes may affect the viscosity of the oil and its ability to uptake water. These chemical compositions also imply significant changes to the ecological effects of the oil following a spill when aged in sunlight.
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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".