Hydrogen Isotope Fractionation during Methanogenic Degradation of Toluene: Potential for Direct Verification of Bioremediation
Bibliographic record
Abstract
Equilibrium headspace analysis of toluene for δ 2 H isotopic composition by continuous flow compound specific isotope mass spectrometry was determined to have an accuracy and reproducibility of ±5‰. Using this analytical approach, the hydrogen isotope fractionation produced by anaerobic biodegradation of toluene was evaluated in laboratory experiments using a mixed methanogenic consortium. A large, reproducible 2 H-enrichment in the residual toluene of greater than 60‰ was observed at greater than 95% degradation, reflecting the preferential biodegradation of molecules containing the light ( 1 H) isotope. Recent studies evaluating the magnitude of carbon isotope fractionation produced during biodegradation of aromatic hydrocarbons have documented heavy isotope ( 13 C) enrichment in the residual contaminant approximately an order of magnitude smaller than those reported here for 2 H. The very large isotopic enrichment in 2 H suggests that under anaerobic conditions compound specific hydrogen isotope analysis may provide a more reliable means of validating intrinsic bioremediation of aromatic hydrocarbons than stable carbon isotope analysis. Combined application of stable carbon and hydrogen isotope analysis in an anaerobic groundwater has the potential to provide two important diagnostic tools. Relatively insensitive to biodegradation by mixed consortia, stable carbon isotope values may provide information about different sources of contaminant, while hydrogen isotope values provide an assessment of the degree of attenuation due to biodegradation.
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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".