Get the MERCURY Out!
The Effects of Mercury on the Nervous System

What is Mercury?

Mercury is a metal that has been used in products such as light bulbs, batteries, paint and thermometers. Although quite useful, mercury is also poisonous and can contaminate the environment if it is not disposed of properly. There are several forms of mercury:
  1. Elemental (metallic) mercury: shiny, silver, odorless liquid used in thermometers. It is absorbed by the body through vapors.

  2. Organic mercury: mercury combined with carbon. Methyl mercury is a common form of organic mercury. These forms of mercury are soluble in lipids and cross the blood brain barrier and placenta easily. Organic mercury is absorbed through the digestive tract and also through vapors.

  3. Inorganic mercury: mercury combined with non-carbon substances. Mercury salts are one kind of inorganic mercury. Inorganic mercury is usually a white powder or crystals. This form of mercury has been used in medicines. Mercuric nitrate was used by the felt-hat industry in the process of curing felt. People in the felt-hat industry sometimes showed signs of mercury poisoning and came down with "Mad-Hatter" syndrome. This is where the phrase "mad as a hatter" originated and was the basis for the "Mad Hatter" character in Lewis Carroll's book Alice in Wonderland.

Different types of mercury affect people in different ways. Organic mercury is more dangerous than inorganic mercury, but many inorganic mercury compounds can be converted to the organic type.

Where is Mercury Found?

  1. Mercury is a natural material found in the earth. Some mercury vapors are given off during volcanic eruptions.

  2. Mercury is a by-product of coal-burning power plants. Mercury is released into the air, then it falls back to the earth.

  3. Mercury is used by mining operations to separate gold from impurities in ore.

  4. Mercury is used during the manufacture of various products. For example, before 1990, mercury was added to paint.

How Are People Exposed to Mercury?

  1. Breathe mercury fumes.

  2. Eat food (especially fish) or drink water that has been contaminated by mercury. Mercury is absorbed by fish through their gills. Mercury also makes its way up the food chain when fish eat plankton or smaller fish that are already contaminated. Fish that are commonly found with high levels of mercury include shark, swordfish and large tuna. The United States Food and Drug Administration has set a limit on the amount of mercury (1 part per million) that cannot be exceeded in fish intended for human consumption.

  3. Absorb mercury through the skin. Glass thermometers contain mercury that should be cleaned up properly (see below).

  4. Eat objects that contain mercury. For example, small children may eat batteries that contain mercury. Broken high power lights and long fluorescent tubes can also contain mercury. Small amounts of mercury from these sources may be ingested accidentally.
Mercury levels within a person's body can be measured in blood, urine and hair samples. The normal level of mercury for someone who has not been exposed to mercury is about 2 ppm (hair) or 3-4 ug/dl of blood or 25 ug/l or urine. When levels get to about 50 ppm (hair), people may start to experience nerve damage. Because hair continues to grow, it can be used to document when and how much a person has been exposed to mercury.

How Does Mercury Affect the Nervous System?

Methyl mercury targets and kills neurons in specific areas of the nervous system including the:
Visual cortex
Cerebellum
Dorsal root ganglia

Several mechanisms have been proposed to explain how mercury kills neurons:

  1. Protein inhibition
  2. Disruption of mitochondria function
  3. Direct affect on ion exchange in a neuron
  4. Disruption of neurotransmitters
  5. Destruction of the structural framework of neurons

Methylmercury is especially dangerous to developing babies. This form of mercury is highly toxic and can cross the placenta and the blood-brain barrier. Mercury is concentrated in the brain of the developing fetus because the metal is absorbed quickly and is not excreted efficiently. Children exposed to mercury may be born with symptoms resembling cerebral palsy, spasticity and other movement abnormalities, convulsions, visual problems and abnormal reflexes. The brains of children who have died as a result of mercury poisoning show neuron loss in the cerebellum and throughout the cerebral cortex. Mercury also appears to affect brain development by preventing neurons from finding their appropriate place in the brain. Human Brain
32 week old fetus

Image courtesy of The Slice of Life

Mercury Disasters

Several disasters have occurred when mercury found its way into the food supply.
  1. Minamata Bay (Japan): Organic mercury was dumped into Minamata Bay in the 1950s. Fish in the bay were contaminated and about 2,000 people who ate these fish became poisoned. About 7% of the children born to mothers who ate contaminated fish had neurological problems. Symptoms in these children included uncoordinated movement, abnormal reflexes, seizures and speech problems. Some adults also had neurological problems such as visual disorders, shaking (tremors), weakness, nausea, hearing loss, depression, confusion, loss of appetite and memory problems. A total of 46 people died as a result of mercury exposure.

  2. Iraq: In 1972, approximately 6,500 people fell ill and 459 people died after eating bread baked with wheat contaminated with a mercury-based fungicide.

  3. Faroe Islands (North Atlantic): A study started in 1984 investigated the effects of methyl mercury exposure on children born to mothers who ate contaminated whale meat. Researchers found that children (seven years old) who were born to mothers with a 10-20 ppm mercury count had lower language, attention and memory scores than those children born to mothers with lower mercury levels. Interestingly, a study performed in the Seychelles Islands (Indian Ocean) did not reveal any effects on children born to mothers who had mercury hair levels of 10 ppm.

Can You Get Contaminated by Mercury if you Have Dental Fillings?

Tooth cavities are most often filled with dental amalgam. Dental amalgam is made with several different materials including silver, tin, copper and mercury. When these materials are combined, they form a stable substance. Used for over 150 years, dental amalgam has proved to be an effective and relatively inexpensive way to repair damaged teeth. Because dental amalgam contains mercury, some people have been concerned that they can be poisoned by tooth fillings. However, the American Dental Association has reviewed the literature and has concluded that dental amalgam is a safe way to repair teeth, unless you are allergic to one of the materials in amalgam. The US Public Health Service, Centers for Disease Control and Prevention (CDC) and Food and Drug Administration have reached similar conclusions.

How To Clean Up Mercury from a Broken Thermometer

  1. Take off any jewelry so you don't contaminate it.
  2. Scoop up the mercury with a sheet of cardboard.
  3. Place the mercury in a small bottle or vial.
  4. Cap the bottle or vial.
  5. Dispose of the bottle or vial properly. Many communities have special hazardous waste disposals or pick-up locations.
  6. Wash your hands!
  7. NEVER use a vacuum cleaner to clean up mercury spills. A vacuum cleaner will get contaminated and will spread mercury vapors into the air.

Did you know?

  • The cities of Ann Arbor (Michigan) and Duluth (Minnesota) have banned the sale of mercury thermometers. (Reference: Newsweek magazine, August 14, 2000, page 67)

  • The chemical symbol for mercury is Hg. Hg comes from the Latin word, hydrargyrum, meaning "liquid silver."

  • Mercury has a boiling point of 357oC (675oF) and a melting point of -38.8oC (-37.9oF).

References and Further Reading about Mercury:

  1. Mercury Study Report to Congress
  2. The Vulnerable Brain and Environmental Risks, Volume 2: Toxins in Food, edited by R.L. Isaacson and K.F. Jensen, Plenum Press, New York, 1992.
  3. Thimerosal in Vaccines - from the FDA

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