Environmental Effects

    Mercury exists in three forms in the environment:  elemental mercury, organic mercury, and inorganic mercury.  In the environment, mercury may be converted from one form to another through oxidation/reduction and 

methylation/demethylation reactions.

• The global contribution of mercury emissions to the atmosphere from man made sources is 2,000 to 4,000 tons per year (tpy).  The amount from natural resources is similar.
• 87% of the anthropogenic contribution is from combustion (waste and fossil fuels).
• 33% of the U.S. contribution is from utilities.
• The EPA identified electric utilities as the largest remaining non-environmental source of mercury into the air 
• Water accumulation is emphasized because consumption of water-based organisms is the main way humans are exposed to mercury released by utility plants.
• In1998, 84% of the deposition in Lake Michigan was atmospheric.

• Methylated mercuries are the most important form of mercury when dealing with toxicity and exposure.

o       Hg²⁺ contributes the most to methylmercury.  It is highly soluble in water and so is easily transported from the atmosphere by rain.

o       Nearly all mercury that accumulates in fish is methylmercury.

o       Rain can contain as much as 30x the EPA’s level of safe mercury.

• Concentrations in water bodies greatly vary depending on the region of the U.S., proximity to local sources, weather, characteristics of the water and associated organisms, season, wind pattern, and the geography of surrounding land.
• A 1 yr. study of Lake Champlain found that half of total amount of mercury exported to connecting streams and rivers for that year happened in one day.  This was due to a peak snow melt.
• Various studies of mercury concentrations in fish and water have found that levels greatly differ among sites.
• Anthropogenic deposition in the North East is from:
•  47% local
• 30% outside
• 23% global reservoir

Diagram of how Hg spreads in our environment