Aquatic toxicity and chemical fate of diluted bitumen spills in freshwater under natural weathering
Bibliographic record
Abstract
Increasing global demands for oils are fueling the production of diluted bitumen (DB) from Canada’s oil sands region. More weathered than conventional crude (CC) oils, Alberta bitumen is often diluted with lighter petroleum oils to reduce density and viscosity to meet pipeline specifications for transportation. Being a heavy oil product that is transported in large volumes across Canada and the USA, there has been interest to compare its behavior and toxicity characteristics when spilled to those of CC. To determine the influence of environmental weathering upon DB following a freshwater spill, we conducted separate controlled spills of Cold Lake Blend DB and Mixed Sweet Blend light CC oil in a mesocosm spill-tank system at 24 °C with wave-action for 56 days. DB-contaminated waters remained acutely lethal for a period of 14 days to early life stage fathead minnows (Pimephales promelas) exposed during embryologic development, while CC was lethal for 1 day. However, concentrations of mono- and polycyclic aromatic compounds, often claimed to be principally responsible for the acute and chronic toxicity of crude oils, were consistently higher in CC water compared to DB. Elevated aromatic concentrations in CC water correlated with higher prevalences of developmental malformations, reduced heart and growth rates, and impacts on the aryl hydrocarbon receptor pathway. Organic acids were measured over the course of the studies and O2 containing naphthenic acids were present at greater relative abundances in DB- compared to CC-contaminated water, with their attenuation correlating with reduced acute and sublethal toxicity. Furthermore, organic acid degradation products accumulated with time and likely contributed to the consistently sublethal toxicity of the weathered oils throughout the experiment. Improved characterization of the fractions including organic acids and those organic compounds found within the unresolved complex mixture of fresh and weathered crude oils is necessary to adequately understand and prepare for the risks that accidental petroleum spills pose to aquatic resources.
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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".