What are the main factors affecting mercury methylation and what is their relative importance?

Question

What are the main factors affecting mercury methylation and what is their relative importance?

Answer 1

It's a complicated but very important process.

The Environment Canada website cited below has a pretty good discussion:

"Understanding the variables influencing the formation of methylmercury is critically important due to its highly toxic, bioaccumulative and persistent nature. A variety of microorganisms, particularly methanogenic (methane producing) and sulfate-dependant bacteria are thought to be involved in the conversion of Hg2+ to MeHg under anaerobic (oxygen poor) conditions found, for example, in wetlands and river sediments, as well as in certain soils. Methylation occurs primarily in aquatic, low pH (acidic) environments with high concentrations of organic matter.

"Rates of biomethylation are a function of environmental variables affecting mercuric ion availability as well as the population sizes of methylating microbes. Alkalinity, or pH, plays a strong role in regulating the process because it is affected by, and in turn effects, the adsorption of various forms of mercury on soil, clay and organic matter particles, thus influencing mercuric ion availability. Acid rain may increase biomethylation as more MeHg is formed under acidic conditions. Mercury can be bound by sulfide ions and made unavailable for methylation; however, sulfate may stimulate growth of certain methylating microbes. Organic matter can stimulate microbial populations, reduce oxygen levels, and therefore increase biomethylation. Biomethylation increases in warmer temperatures when biological productivity is high, and decreases during the winter."