Mercury In Our Waterways

Mercury is a heavy metal element that can have serious effects on our waterways and aquatic ecosystems. It is a neurotoxin that has an effect on fish, wildlife, and humans. But how does mercury get into our waterways? The main source of mercury is from atmospheric deposition that is contracted through rain, snow, and dry particles. How does mercury, a very dense metal, float freely in our atmosphere? The USEPA states that coal fired power plants are the leading contributor of mercury to the atmosphere.

Another source of mercury are point source discharges. These point source discharges include pipes, ditches, and stormwater infrastructure. It is important to note that pollutants that are disposed of in storm drains, such as mercury, will adversely affect our waterways. Most of us don’t deal with elemental mercury for scientific purposes, but what products do we use that contain mercury? Some very common products include:

  • Fluorescent light bulbs and lamps (including CFLs)
  • Certain types of batteries (button cell and mercuric oxide)
  • Thermometers
  • Thermostats
  • Certain pharmaceuticals (as an antibacterial agent, it’s even toxic to a lot of microorganisms!)

For proper disposal/recycling techniques for mercury and mercury containing products, please click here.

Why is mercury so toxic? Are fish unsafe to eat?

The reason mercury is so toxic is because of a process called Methylation, a change from inorganic mercury to organic mercury (methylmercury). Most mercury is atmospherically deposited as inorganic mercury. This inorganic mercury can either settle out and become part of the sediment record in lakes and dam pools, or can be converted to methylmercury by aquatic biota. Once in the water, mercury is assimilated by organisms such as algae, and then is consumed by organisms higher up on the food chain, such as fish, and eventually us humans. Mercury is taken in by the organisms and stored in fat and muscle tissues. Bioaccumulation occurs when an organism absorbs mercury in their tissues faster than it is removed. Biomagnification can also occur, which basically means that as animals up the food chain eat the organisms lower on the food chain containing mercury, larger amounts of mercury stored within the higher level organism. Both bioaccumulation and biomagnification affect humans because we consume fish that may have a stored large amounts of mercury in their tissues because of these processes.

Methylmercury is a neurotoxin that interferes with both the brain and nervous system. Possible symptoms of methylmercury may include loss of peripheral vision, “pins and needles” in the hands and feet, loss of coordination of movements, and muscle weakness, impairment of speech, hearing, and walking. As with other toxins, such as lead, the effects of mercury are greater with children. Infants exposed to mercury have impacts to their cognitive thinking, memory, attention, language, fine motor skills, and visual spatial skills.

Some fish are unsafe to eat because of their high levels of mercury. Some geographic areas may be better than others for catching and eating fish. A resource containing information on types of sport fish to eat and how often is available from Ohio EPA Division of Surface Water. The USEPA also has a website on fish consumption advisories and technical articles. Fish is an important part of a healthy diet, so being informed about mercury in sport fish is necessary.

Where do we find high mercury concentrations in fish?

High levels of mercury are most commonly found in fish in Eastern US states with a high density of forest and wetlands in the stream basin and in waters with large sources of mercury such as urban areas and areas with historical mining of gold or mercury. Common places in northeast Ohio to sport fish in are listed in the photos with advisories on consumption rate.

Take home message

Mercury is a neurotoxin that can have adverse effects on humans, especially children of a young age. The largest source of mercury is from coal fired power plants, and in recent years, the USEPA has taken steps to minimize mercury output from these power plants. After mercury enters into a waterway from atmospheric deposition or by another means, it can settle out as part of the sediment record or become methylmercury, which is the most toxic. Mercury can Bioaccumulate or Biomagnify in organisms, both of which lead to higher amounts of mercury that can be consumed by humans. It is important to be informed about mercury in our water ways and to limit sport fish intake. For further reading on mercury, side effects, and legislation regarding mercury, see the references below.


Advisories and Technical Resources for Fish and Shellfish Consumption

Health Effects of Exposures to Mercury

List of Common Consumer Products that Contain Mercury

Recycling and Disposal Options

Ohio Sport Fish Consumption Advisory

Why is Mercury in Fish Such a Problem Today?

Mercury in Aquatic Systems

Photo credits

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Blog author: Adam Delaney, Natural Resources Intern

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