Microbes and Mercury
If you’ve taken Chemistry classes, used a thermometer, or read about seafood warnings, you have probably heard of mercury, or Hg. #80 on the Periodic Table, Hg is the only metal that is liquid at standard temperature and pressure! While Hg is a naturally occurring element, it is considered to be a pollutant. It is released through different processes- when volcanoes erupt, people mine for gold, fossil fuels are burned. Once it evaporates, Hg travels throughout the atmosphere, and eventually settles down in soil and bodies of water.
Well, once it’s out in the environment, Hg can cause some damage! Hg has different forms, and not all are created equal. Hg can stand alone, with a neutral or positive charge. Inorganic forms can include oxygen or sulfur. The organic forms, which contain carbon attached to the Hg, are more dangerous to wildlife. Methylmercury, also known as MeHg or CH3Hg, is arguably the worst offender. What is it that makes CH3Hg so dangerous? When animals eat something containing mercury, it remains in their system for a certain period of time. MeHg stays longest, because of the chemical structure that lets it bind to proteins within animals’ tissues. Unfortunately, this leads to bioaccumulation (when the concentration builds up in an animal as it gets older) and biomagnification (when animals at the top of the food web have increasingly high concentrations). If an organism has above a certain concentration of Hg, they may suffer from mercury poisoning. Symptoms include numbness, tremors, weakness, and reproductive effects, among others.
By now you may be wondering- how does the methyl (CH3) get attached to the mercury (Hg)? The answer is through tiny yet powerful microbes! The microbes collect the Hg, and proteins initiate a chemical reaction adding the CH3 to the Hg. We can blame various species from these groups: sulfate-reducing, iron-reducing, and methanogenic, or methane producing bacteria. They tend to grow better in certain environments. They feel at home in water bodies that are acidic, low in oxygen, and high in sulfate. Conversely, water bodies that receive more oxygen and sunlight will not be as welcoming.
Understanding the connection between microbes and Hg helps us determine whether it is safe to go fishing in certain areas. Also, it helps us find ways to decrease Hg, such as oxygenating a lake to make it less friendly for the methylating microbes!
