Photochemical Mass Balance of 2,3,7,8-TeCDD in Aqueous Solution under UV Light Shows Formation of Chlorinated Dihydroxybiphenyls, Phenoxyphenols, and Dechlorination Products
Bibliographic record
Abstract
Polychlorinated dibenzo-p-dioxins (PCDDs) are a class of halogenated diaryl compounds that are environmentally important because of their high toxicity and bioaccumulatory properties. There is an incomplete understanding of their photochemistry because the majority of photoproducts, as indicated by incomplete mass balances, have not been identified. We studied the photochemical transformation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TeCDD) in aqueous solution using 302 nm light. Our results allow for the first photochemical mass balance (92-99%) for this compound and confirm the operation of a novel photochemical pathway, which gives rise to 2,2'-dihydroxy-4,4',5,5'-tetrachlorobiphenyl (4,4',5,5'-TeCDHBP) at >50% conversion from the starting material. Rearrangement from 2,3,7,8-TeCDD to 4,4',5,5'-TeCDHBP takes place following preferential homolytic C-O bond cleavage via a proposed mechanism analogous to the parent dibenzo-p-dioxin system. Photochemical conversion from the starting material to dechlorinated PCDDs or chlorinated phenoxyphenols are minor pathways, although the exact contribution of the strictly dechlorination pathways remains uncertain because of the complexity of the system. The results suggest that the photochemical conversion of PCDDs to chlorinated dihydroxybiphenyls, which are also polychlorinated biphenyl (PCB) metabolites, may be an important part of their environmental fate.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.002 | 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".