Bibliographic record
Abstract
Abstract. Sorption of mercury (Hg) in soils is suggested to be predominantly associated with organic matter (OM). However, there is a growing collection of research that suggests clay minerals and Fe/Mn-oxides are also important solid-phases for the sorption of soluble Hg in soil-groundwater systems. We use a series of (60 mL syringe based) column experiments to examine sorption and subsequent desorption of HgCl2 solutions (Experiment 1 [EXP1]: 46.1 ± 1.1 mg L-1; and Experiment 2 [EXP2]: 144 ± 6 mg L-1) in low OM (0.16 ± 0.02 %) solid-phase aquifer materials. Analyses of total Hg concentrations, Hg speciation (i.e., pyrolytic thermal desorption (PTD)), and Hg stable isotopes are performed on both solid- and liquid-phase samples across sorption and desorption phases. Sorption breakthrough curve best fitted a Freundlich model. Despite the very low OM content, the Hg equilibrium sorptive capacity in these columns is very high: 1510 ± 100 and 2320 ± 60 mg kg-1 for the EXP1 and EXP2, respectively, and is similar to those determined for high OM soils. Desorption fits exponential decay models and 46 ± 6 % and 58 ± 10 % of the sorbed Hg is removed from the solid-phase materials at the termination of desorption in EXP1 and EXP2, respectively. This desorption profile is linked to the initial release of easily exchangeable Hg(II) species physically sorbed to Fe/Mn-oxides and clay mineral surfaces and then slower release of Hg(II) species that have undergone secondary reaction to more stable/less soluble Hg(II) species and/or diffusion/transport into the mineral matrices. Hg stable isotope data support preferential sorption of lighter isotopes to the solid-phase materials with results indicating isotopically heavy liquid-phase and isotopically light solid-phase. The divergence of δ202Hg (describing mass dependent fractionation (MDF)) between liquid- and solid-phase continues into desorption and we attribute this to lighter isotopes being favoured in secondary processes occurring after initial sorption to the solid-phase materials (i.e., matrix diffusion, change in Hg(II) speciation, elemental Hg (Hg(0)) production) that lead to less exchangeable forms of Hg. Consequently, heavy isotopes are preferentially released during desorption. These observations agree with data from HgCl2 contaminated sites. The secondary production of Hg(0) within the columns is confirmed by PTD analyses that indicate distinct Hg(0) release peaks in solid-phase samples at <175 °C, which again agree with field observations. Retardation (RD) and distribution (KD) coefficients are 77.9 ± 5.5 and 26.1 ± 3.0 mL g-1 in EXP1, respectively, and 38.4 ± 2.7 and 12.4 ± 0.6 mL g-1 in EXP2, respectively. These values are similar to values derived from column experiments on high OM soil and provide the basis for future Hg fate and transport modelling in soil-groundwater systems.
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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 | 0.003 | 0.025 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.003 | 0.003 |
| Scholarly communication | 0.005 | 0.004 |
| Open science | 0.004 | 0.003 |
| Research integrity | 0.029 | 0.025 |
| Insufficient payload (model declined to judge) | 0.178 | 0.140 |
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".