Bibliographic record
Abstract
The most important mercury species in the environment is monomethylmercury (MMHg), the topic of this chapter. This organic mercury compound is normally not released into the environment but formed by natural processes. Mercuric mercury (Hg2+) is methylated by bacteria and to a lesser extent through abiotic pathways. Highest rates of formation are found in anoxic aquatic environments. Terrestrial systems are mostly irrelevant for MMHg production and not a concern. Most productive environments are sediments, wetlands, and coastal marshes, but also the anoxic hypolimnion of lakes and anaerobic microhabitats like the rhizosphere of floating macrophytes. Prime suspects for methylation are sulfate-reducing bacteria, although also iron reducers have lately been identified as capable mercury methylators. What makes methylmercury such an insidious contaminant is its enormous biomagnification potential. Methylmercury is accumulated by more than seven orders of magnitude from sub ng/L concentrations in water to over 1,000,000 ng/kg in piscivorous fish, which are the main concern from a human health point of view. Since methylmercury is a very potent neurotoxin, particularly small children, pregnant women, and women in childbearing age are advised to either limit their fish consumption to a few meals per week or to select fish species known to have low levels of methylmercury. Formation of methylmercury is counteracted by other bacteria, which are capable of demethylating methylmercury. This process is regulated by an inducible mer operon system and serves as a detoxification mechanism in polluted environments. The other naturally occurring organic mercury species, dimethylmercury (DMHg), is only present at very low levels at great depths in the world oceans. However, it might be an important and very mobile pre-cursor for methylmercury in marine and polar ecosystems.
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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) | 0.001 | 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 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.012 | 0.008 |
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".