Insights from multiple stable isotopes (C, N, Cl) into the photodegradation of herbicides atrazine and metolachlor
Bibliographic record
Abstract
Many processes can contribute to the attenuation of the frequently detected and toxic herbicides atrazine and metolachlor in surface water, including photodegradation. Multi-element compound-specific isotope analysis has the potential to decipher between these different degradation pathways as Cl is a promising tool for both pathway identification and a sensitive indicator of degradation for both atrazine and metolachlor. In this study, photodegradation experiments of atrazine and metolachlor were conducted under simulated sunlight in buffered solutions (direct photodegradation) and with nitrate (indirect photodegradation by OH radicals) to determine kinetics, transformation products and isotope fractionation for C, N and for the first time Cl. For metolachlor, the C–Cl dual isotope slope (Λ C/Cl = 0.46 ± 0.19) is identical to previously reported values for hydrolysis and biodegradation in soils, suggesting the same reaction mechanism (C–Cl bond breakage by SN 2 nucleophilic substitution). For atrazine, both direct and indirect photodegradation resulted in a pronounced inverse isotope effect for chlorine (ε Cl = 6.9 ± 3.3 ‰, and ε Cl = 2.3 ± 1.2 ‰, respectively), leading to characteristic dual isotope slopes (Λ C/Cl = −0.49 ± 0.17 and Λ C/Cl = −0.31 ± 0.10, respectively). These values are distinct from those previously reported for abiotic hydrolysis, biotic hydrolysis and oxidative dealkylation which are all relevant processes in surface water, opening the path for pathway identification in future field studies. • Photodegradation experiments on atrazine and metolachlor under simulated sunlight. • First report of Cl isotope fractionation associated to photolysis of herbicides. • Inverse isotope effect for Cl during atrazine direct and indirect photodegradation. • Dual C–Cl isotope plot allows pathway identification for atrazine in surface water. • Cl data suggest common reaction mechanism to different pathways for metolachlor.
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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".