Chiral Current-Use Herbicides in Ontario Streams
Bibliographic record
Abstract
Concentrations of mecoprop, dichlorprop, and metolachlor were investigated in 393 samples from Ontario streams in 2003-2004. Maximum concentrations of mecoprop, dichlorprop, and metolachlor were 1900, 6.62, and 1560 ng L(-1), respectively in 2003, and 103,000, 110, and 5290 ng L(-1), respectively, in 2004. Concentrations of metolachlor in agricultural watersheds were significantly (p < 0.0001) higher than those in urban watersheds, whereas concentrations of mecoprop did not differ (p > 0.1) between the two watershed types. Enantiomer fractions (EFs) of the acid herbicide mecoprop ranged from 0.236 to 0.928 and for dichlorprop EFs ranged from 0.152 to 0.549. EFs of mecoprop did not differ significantly (p > 0.1) between agricultural and urban land usage. Mecoprop EFs > or = 0.5 were found in 54% of samples, a situation expected during the transition years when racemic mecoprop was replaced by mecoprop-P, consisting of only the R(+) enantiomer. However, EFs < 0.5 were found in 46% of samples, which suggests preferential degradation of R(+) or conversion of R(+) to S(-). The four stereopluisomers of metolachlor were separated by HPLC and are reported as the ratio of the two herbicidally active stereoisomers (aS,1'S and aR,1'S) to the two inactive stereoisomers (aS,1'R and aR,1'R). The average S/R of metolachlor in streams was 6.73 +/- 2.28 and ranged from 1.08 to 12.7. Samples with higher concentrations of metolachlor had S/R ratios similar to the S/R of S-metolachlor (enriched in aS,1'S and aR,1'S stereoisomers) whereas samples with lower concentrations display lower S/R ratios with greater variability, suggesting mixed input of racemic and S-metolachlor or stereoselective degradation. S/R values were significantly higher (p < 0.001) in agricultural than urban watersheds. Streamwater from row crop areas showed higher S/R ratios than streamwater from fruit growing areas (p = 0.036).
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".