Evaluating the photo-enhanced toxicity of diluted bitumen and conventional heavy crude spills to freshwater organisms.
Bibliographic record
Abstract
The majority of Canada’s oil is extracted from the Alberta Oil Sands region, with the main products being diluted bitumen (dilbit) and conventional heavy crude (CHV). These products are transported across North America primarily by pipelines and rail. The effects of these petroleum products on freshwater environments after accidental spills are still poorly understood, even though the risks of oil spills into fresh water are increasing with more pipeline and rail transportation. Information regarding the efficacy of alternative remediation strategies for freshwater environments, particularly shorelines, are also lacking. This thesis addresses the effects of freshwater dilbit and CHV spills alone and in combination with ultraviolet (UV) radiation to evaluate the photo-enhanced toxicity (PET) of these oils. Model oil spills were conducted as a part of the IISD-Experimental Lakes Area (IISD-ELA) Freshwater Oil Spill Remediation Study (FOReSt) to evaluate minimally invasive remediation methods for shoreline environments after oil spills. Species with established sensitivities were chosen to evaluate the water accommodated fraction (WAF) of these oils before and after remediation, including Hyalella azteca and wild fathead minnows (FHM; Pimephales promelas). Juvenile Hyalella azteca were exposed to WAFs of weathered dilbit and CHV with various remediation treatments, including the surface washing agent (SWA) Corexit EC9580A and nutrient additions, referred to as enhanced Monitored Natural Recovery (EMNR). Dilbit and CHV both exhibited PET to Hyalella azteca by decreased growth and increasing mortality at lower lethal concentrations, measured as the concentration required to reach 50% mortality (low UV LC50s of 14,162 ng L-1 and 4761 ng L-1 compared to high UV LC50s of 9466 ng L-1 and 484 ng L-1 for dilbit and CHV respectively). Individuals exposed to Corexit EC9580A and its active surfactant dioctyl sodium sulfosuccinate (DOSS) incorporated bubbles internally and externally, disrupting buoyancy and increasing mortality. Early life-stages of wild FHMs were also exposed to WAFs of dilbit to evaluate its PET to a wild collected species at lower concentrations after remediation. Three exposure rounds were conducted at increasing post-oil spill intervals (12-, 20-, and 38-days post spill). FHM mortality was similar among all treatments, including the reference treatment, and lethal concentrations did not significantly differ between UV groups, however, the high UV group did have a lower LC25. In the last round, individuals in the high UV group had increased mortality compared to their low UV group counterpart, suggesting increased PET. Individuals in dilbit and dilbit with high UV treatments did exhibit significantly upregulated cyp1A expression and increases in malformations, particularly yolk sac edemas, cardiac malformations, and deflated swim bladders, indicating potential PET at sub-lethal levels. However, individuals exposed to the more weathered dilbit in later rounds showed phototoxic trends of increased mortality, upregulated cyp1A and thyroid related genes, and increased malformations, indicating dilbit photodegradation and weathering may potentially cause more PET. The results of these studies emphasize the importance of conducting toxicity testing under environmentally-relevant conditions, as real-world factors, such as UV radiation, can impact the toxicity to organisms in natural environments where accidental spills occur.
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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 | 0.000 | 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 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".