Zinc−Sulfur and Cadmium−Sulfur Association in Metalliferous Peats: Evidence from Spectroscopy, Distribution Coefficients, and Phytoavailability
Bibliographic record
Abstract
Peat deposits can concentrate chalcophilic metals such as Zn and Cd by biogeochemical processes; as a result, there is a possibility that the solubility, mobility, and bioavailability of these metals could increase when such deposits are drained and cropped, initiating oxidation of organic matter and sulfides under aerobic conditions. We use spectroscopic, chemical, and bioassay approaches to characterize high Zn (88-15,800 mg kg(-1)), Cd (0.55-83.0 mg kg(-1)), and S (3.52-9.54 g kg(-1)) peat soils collected from locations in New York State and Ontario that overlie Silurian-age metal-enriched dolomite bedrock. Total and KNO3-extractable trace metals were determined by ICP emission spectrometry, and labile Cd and Zn were measured in the KNO3 extracts by anodic stripping voltammetry. A greenhouse bioassay with maize and canola was conducted to determine the bioavailability and toxicity of the soil Zn and Cd. The electronic oxidation states of sulfur in the peat soils were determined by X-ray absorption near edge spectroscopy (XANES) and Zn and S distribution in soil particles by energy-dispersive X-ray absorption (EDX) spectroscopy. Sulfur-XANES analyses show that a high percentage (35-45%) of the total soil S exists in the most reduced electronic oxidation states (such as sulfides and thiols), while <5% exists in the most oxidized forms (such as sulfate). EDX analyses indicate a microscopic elemental association between Zn and S in these soils. Despite the EDX evidence of close association between Zn and S in soil particles, conventional X-ray diffraction analyses of the bulk soils did not detect a mineral phase of sphalerite (ZnS) in any of the soils. The distribution coefficients (Kd) for Zn and Cd increased with soil pH and indicated stronger Cd retention than Zn in the peats. The results of the bioassaytests showed that most of the high-Zn soils were very phytotoxic, with plant shoot Zn levels exceeding 400 mg kg(-1). Conversely, Cd concentrations in the plant shoots were generally below 2 mg kg(-1), showing a tendency toward low Cd phytoavailability relative to Zn. The information gained from the spectroscopic analyses (S-XANES and EDX) was used to explain the macroscopic observations (Cd and Zn Kd values and phytoavailability data) in these peat soils; we conclude that sulfur biogeochemical cycling may play an important role in Zn and Cd retention in these organic soils.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.004 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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 teacher head, 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".