Redistribution of Polychlorinated Biphenyls from a Local Point Source: Terrestrial Soil, Freshwater Sediment, and Vascular Plants as Indicators of the Halo Effect
Bibliographic record
Abstract
Polychlorinated biphenyl (PCB) concentrations and congener profiles in terrestrial soils, vascular plants, and freshwater lake sediments were compared with respect to their relative utilities for assessing the redistribution of PCBs from a local contaminant source into the surrounding arctic environment.Plants (n = 62), soils (n = 58), and surficial freshwater lake sediments (n = 16) were collected at varying distances up to 27 km from the source at Saglek, Labrador. Total PCB concentrations in these media exhibited similar negative log-linear relationships with increasing distance from the contaminant source. Analysis of congener compositions indicated that plants are more reflective of recent PCB exposure than either soils or sediments. Vascular plants reflect current ambient contaminant concentrations, whereas terrestrial soils and freshwater sediments represent much longer periods of contaminant deposition and are further influenced by such factors as their organic carbon content, particle size distribution, lake watershed size and productivity (in the case of sediments), and proximity to a drainage course (in the case of soils). Collectively, the data indicate that short-range transport of PCBs at Saglek has resulted in a halo of contamination that is up to 50 km in diameter.
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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 | 0.000 | 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) | 0.000 | 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".