Historical Perspective of Industrial Lead Emissions to the Atmosphere from a Canadian Smelter
Bibliographic record
Abstract
Dated sediment cores from four remote Canadian Shield headwater lakes, where atmospheric deposition has been the only input of anthropogenic Pb, situated along a transect extending 300 km from a nonferrous metal smelter, were analyzed for both lead concentrations and isotopic composition; porewater samples collected at the same sites were analyzed for Pb and other geochemical variables. The depth distributions of stable Pb isotope ratios show the presence of several isotopically distinct Pb types since the preindustrial period. Lead from the smelter emissions had an isotopic signature (e.g., 206Pb/207Pb approximately 0.993) that was clearly distinct from those of Pb in aerosols collected at sites remotefrom point sources in Eastern Canada (e.g., 206Pb/207Pb usually approximately 1.15-1.20) and the United States (e.g., 206Pb/207Pb usually approximately 1.15-1.22), allowing the geographical area impacted by the smelter Pb emissions to be traced. On the basis of the sediment Pb isotopic composition, it is estimated that lead from the smelter accounts for 89%, 88%, and 5-34% of the total inventory of anthropogenic Pb deposited in the sediments of lakes located 10, 25, and 150 km from the smelter, respectively; but lead from this point source was not detected in sediments of a fourth lake that is 300 km from the smelter. We also estimate that the amount of smelter-derived Pb deposited within a distance of 150 km is equivalent to 5-10% of the amount released by leaded gasoline combustion in all of Canada. Sharp decreases in the recent Pb fluxes to lake sediments indicate that the measures taken to mitigate metal emissions from the smelter were effective.
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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 | 0.002 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".