Example Data Table
| Scenario |
Initial IHg |
Initial MeHg |
km |
kd |
Time |
Suggested Method |
| Wetland sediment incubation |
80 ng/g |
3 ng/g |
0.035 day^-1 |
0.020 day^-1 |
14 days |
Closed pool |
| Reservoir water study |
12 ng/L |
0.4 ng/L |
0.018 day^-1 |
0.030 day^-1 |
10 days |
Constant inorganic pool |
| Laboratory bottle test |
50 ng/L |
2 ng/L |
0.050 day^-1 |
0.015 day^-1 |
7 days |
Closed pool |
Formula Used
Temperature correction: k adjusted = k reference x Q10((T observed - T reference) / 10).
Closed pool method: Total Hg = IHg0 + MeHg0.
MeHg(t) = MeHg equilibrium + [MeHg0 - MeHg equilibrium] x e-(km + kd)t.
MeHg equilibrium = km x Total Hg / (km + kd).
Constant inorganic pool method: MeHg(t) = steady MeHg + [MeHg0 - steady MeHg] x e-kdt.
steady MeHg = km x IHg0 / kd.
Net rate at the end: Net rate = km x IHg(t) - kd x MeHg(t).
How to Use This Calculator
Enter the initial inorganic mercury and methylmercury pools in the same unit.
Select the calculation method that matches your experiment or field assumption.
Enter methylation and demethylation constants with their time unit.
Add temperature settings only when Q10 correction is useful.
Use matrix amount to estimate a final burden for water, sediment, or soil.
Press calculate. Results will appear above the form and below the header.
Use CSV or PDF buttons to save the calculated output.
About Mercury Methylation and Demethylation
Mercury cycling is controlled by many linked reactions. Inorganic mercury can become methylmercury when microbes, sulfur chemistry, and organic matter create suitable conditions. Methylmercury is important because it can move through food webs. Demethylation reverses part of that process. It can happen by microbial activity, light, or chemical reactions. A calculator cannot replace sampling. It can organize assumptions and show how sensitive results are.
Why Rate Constants Matter
Methylation and demethylation are often described with first order rate constants. A methylation constant estimates the fraction of available inorganic mercury converted each time period. A demethylation constant estimates the fraction of methylmercury removed each time period. The balance between both constants controls the final methylmercury pool. When methylation is high and demethylation is low, methylmercury rises. When demethylation is stronger, methylmercury falls or stabilizes.
Using the Model Carefully
This tool supports two common screening approaches. The closed pool model keeps total mercury constant. It is useful for bottles, sediment slices, or short tests. The constant inorganic pool model assumes available inorganic mercury remains steady. That approach may suit flowing systems or replenished incubations. Temperature correction can adjust rate constants with Q10 factors. Use this only when the factor is justified by local evidence.
Interpreting Results
The final values are planning estimates. They depend on the selected units, incubation time, and initial pools. Gross methylation and gross demethylation show cumulative process strength. Net change shows whether methylmercury increased or decreased. The equilibrium share shows the direction of long term behavior. Results should be compared with field measurements, blanks, duplicates, and certified methods.
Practical Uses
Researchers can test field hypotheses before laboratory work. Students can understand competing reactions in mercury cycling. Consultants can prepare transparent screening calculations for reports. Managers can compare sites, seasons, or treatment options. Always document assumptions. Keep units consistent. Review unusual outputs carefully before making decisions.
Main Limits
Real systems may include adsorption, diffusion, burial, dilution, photolysis, and changing redox conditions. These factors can shift available mercury during the study period. The model uses simplified pools, so it is best for early estimates. For regulatory work, support calculations with approved sampling, quality control, and expert review. Report every input with its source and date.
FAQs
What does methylation mean?
Methylation is the conversion of available inorganic mercury into methylmercury. It often involves microbial processes. It is affected by organic matter, sulfide, redox state, pH, temperature, and mercury availability.
What does demethylation mean?
Demethylation removes methylmercury or converts it into other mercury forms. It can occur through microbial, chemical, or photochemical pathways. Higher demethylation can reduce the modeled methylmercury pool.
Which method should I choose?
Use the closed pool method for sealed incubations or short tests. Use the constant inorganic pool method when inorganic mercury is replenished or treated as stable during the modeled period.
Can I mix ng/L and ug/g values?
No. Enter initial inorganic mercury and methylmercury in the same unit. The model calculates ratios and changes inside the selected unit. Convert your data before using mixed sources.
What is a rate constant?
A rate constant describes how fast a process occurs. A higher methylation constant increases methylmercury formation. A higher demethylation constant increases modeled removal from the methylmercury pool.
Why include Q10 correction?
Q10 correction estimates how temperature changes may affect reaction rates. Use it only when a reasonable Q10 value is available for your study site, sample type, or literature source.
Are these results regulatory proof?
No. These results are screening estimates. Field decisions should also use approved sampling, laboratory quality control, local guidance, expert review, and documented uncertainty checks.
What does net rate show?
Net rate compares methylation formation against demethylation removal at the final modeled time. Positive values suggest methylmercury is still increasing. Negative values suggest it is decreasing.