What's the problem ?

Mercury, a neurotoxin, is toxic to fish, mammals and humans. Though present at very low levels in the environment it can accumulate in the tissue of fish, people and mammals that consume fish from contaminated waters.

The fate of mercury in the environment depends on its chemical form and environmental conditions.

Read what the world's mercury experts think


Sources of mercury

Mercury, a naturally ocurring metal, is released into the atmosphere from human activities such as mining, burning of fossil fuels like coal, and several industrial uses in chloralkai plants, paints, batteries, medicine and dentistry. These activities have significantly increased global concentrations of atmospheric mercury. Mercury has natural sources as well such as volcanoes, geothermal springs, geologic deposits and the ocean. Though always present at some level before human activity, the levels have increased dramatically, with atmospheric concentrations doubling over the last 150 yrs.

Figure 1. About 70% of the mercury in the atmosphere is released from anthropogenic or human sources. Most of that mercury comes from combustion sources such as coal fired electricity generators and industrial boilers.

Atmospheric deposition of mercury is measured across the US by the Mercury Deposition Network (MDN) There are currently 85 sites. Data has been collected since 1998.

Figure 2. This map shows the concentration of mercury measured in wet precipitation across the US in 2006. Although deposition is declining there are still hot spots in the eastern part of the county.

Species of Mercury

The chemistry of mercury in the environment is very complex and there is a lot about how it moves in the environment that we do not yet understand. What we do know is that mercury comes to the Lake Superior watershed in three principle forms, elemental or Hg(0), ionic Hg(II), and methylmercury. The first two, Hg(0) and Hg (II) are inorganic and are the most mobile forms of this element. Hg(0), also called elemental and gaseous mercury, has a long residence time in the atmosphere traveling globally with the prevailing winds. Hg(0) can be oxidized into the ionic form of Hg (II) by ozone. The ionic form has a much shorter residence time, no longer than 10 days and therefore is more often deposited close to the source. Most of the mercury in the environment is in this inorganic form and is generally not a health concern — it is poorly absorbed by the digestive tract.. The third, methylmercury, is an organic form that is highly toxic to nervous systems of higher organisms.

Figure 3. This schematic from the USGS shows the aquatic mercury cycle.

How and where is methylmercury produced?

Methylmercury is produced by sulfate-reducing bacteria in low oxygenated zones of wetlands and aquatic sediments. This organic mercury is readily accumulated in aquatic biota and biomagnifies to high concentrations in higher trophic levels such as fish eating birds, mammals, and humans. Known sites of methylmercury production include:

  • Low-alkalinity and low-pH lakes
  • Vegetated lowland areas subjected to prolonged inundation, including new reservoirs
  • Wetlands and wetland-influenced waters (dark-water lakes and streams)

Methylmercury is a potent neurotoxin and early life stages are the most sensitive.

Learn more about mercury in Minnesota North Shore streams.

What can you do?

Cut your energy use by using compact fluorescent light bulbs (CFLs). Although these bulbs contain mercury, their proper use and disposal can result in a net decrease in mercury emissions. For more info see Sierra Club's Mr. Green article on the pros and cons of using CFLs.

But remember they need to be recycled in a responsible manner. Where can you take your old bulbs? Click on the bulb to find out (MN Power). Or go straight to the EPA for basic info on CFLs and recycling.

What to do with Mercury containing materials:

  • WLSSD and other regional disposal sites

MPCA Mercury Pollution Prevention

City of Superior

Other household products that contain mercury include:

  • Thermostats and switches
  • Thermometers
  • other fluorescent bulbs (those long skinny ones at the office or in your workshop)
  • Button batteries from watches and hearing aids

Check out this Wisconsin DNR site that shows you where mercury can be within your house.