Occurrence of nitrosamines and their precursors in North American drinking waters
Bibliographic record
Abstract
Abstract Eight N‐nitrosamines were measured at 37 water plants in the United States and Canada. Five tobacco‐specific nitrosamines (TSNAs) were measured in selected waters. N‐Nitrosodimethylamine (NDMA) was preferentially formed in chloraminated systems (maximum detention time: median 4.4 ng/L). A small amount was detected in some chlorinated systems (90th percentile <2.0 ng/L). After ozone (before chloramines), NDMA was sometimes detected (90th percentile 2.9 ng/L), suggesting that the ozone did not react with precursors to form NDMA. The chloramine plants that temporarily switched to chlorine typically produced less NDMA (Plant 29 reduced NDMA formation, on average, from 34 to 4 ng). More NDMA was produced during spring runoff, when there were elevated levels of ammonia and NDMA precursors in the source water. More NDMA was formed when there were higher levels of poly(diallyldimethylammonium chloride) (polyDADMAC) used. N‐Nitrosomorpholene was found to be a contaminant and not a disinfection byproduct; it did not increase during chloramination. TSNAs were produced during spring runoff; source water ammonia impacted the chlor(am)ine chemistry.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 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".