Stable Pb isotopes and PAHs as indicators of lead contaminationsources in a lake of the Rouyn-Noranda area
Bibliographic record
Abstract
We determined the depth distribution of total Pb and its stable isotope composition ($^{206}$Pb/ $^{207}$Pb $^{206}$Pb/ $^{208}$Pb, $^{206}$Pb/ $^{204}$Pb) in a dated sediment core collected at the deepest site, in the hypolimnion of a headwater Canadian Shield lake, located 25 km downstream from a metal smelter in operation since 1927. The isotopic ratios reveal the occurrence of one natural and two anthropogenic types of Pb over the last century. One of the anthropogenic Pb, prédominant in the sediments accumulated in the early 20$^{\rm th}$ century, likely derives from coal combustion ($^{206}{\rm Pb}/^{207}{\rm Pb}\approx 1.185$). The second anthropogenic Pb has a signature similar to that of the ore processed during several decades at the smelter ($^{206}{\rm Pb}/^{207}{\rm Pb} \approx 1.000$); its contribution to the total Pb concentration sharply increased from 1927 to 1975 and then decreased steadily to the sediment surface.
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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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".