Mercury Exposure

Effects on Health


Limiting Mercury Exposure

Exposure in Minnesota

Political Campaign


Who is at risk from mercury exposure?

  • Many factors determine risk from exposure including the dose, duration, and the type of contact.
  • The high risk population of mercury exposure:
    • Pregnant women, or women who may become pregnant in the next few years (the developing fetus) - methylmercury can enter the mother’s body and into the unborn infant and also breast-feeding infants.
    • Young children (less than six years old) – their nervous systems are still developing and have a lower body weight.
    • Adults who consume large amounts of contaminated fish on a daily basis.


Fish and pregnant women:

  • The Food and Drug Administration (FDA) recommends that pregnant women and women who could become pregnant not to eat certain types of fish that have higher levels of mercury. Fish such as shark, swordfish, king mackerel and tilefish should be avoided.
  • In addition, women should continue to avoid eating these types of fish while they breast-feed and avoid feeding them to children ages six and younger.
  • Pregnant women should know the types of fish that are considered safe to consume and follow the recommended fish intake and monitor the amount of fish they eat.

What are the health effects of specific types of mercury?

1. Elemental mercury:

  • Elemental mercury can enter a pregnant woman’s body from breathing contaminated air, which passes into the developing fetus.
  • A higher concentration of mercury vapor inhalation can lead to death from respiratory failures.
  • Heating elemental mercury in inadequately ventilated places can result in fatalities.
  • Long-term exposure to mercury vapor primarily affects the central nervous system.
  • In the story, Alice in Wonderland, the “Mad Hatter” character was based on the brain disease that commonly affected hat makers who used liquid mercury as the treatment of hat felt.
  • Early signs include: insomnia, forgetfulness, loss of appetite, and mild tremor. These may be diagnosed as psychiatric illness.

2. Organic Mercury:

  • Methylmercury can be eaten or swallowed by a pregnant woman and is considered a teratogen in the fetal brain.
  • Methylmercury is a form of mercury that is associated with a risk in developmental effects.
  • Methylmercury can pass from a mother’s body into breast milk and into the nursing infant.
  • Effects of methylmercury may not be apparent if the exposure was small during pregnancy.
    • Small decreases in IQ or effects of the brain that can only be detected by sensitive neuropsychological testing.
  • In greater instances, the effects could be more serious if the exposure is high during pregnancy.
    • Exposure to a developing fetus may show effects when they are beginning to walk or talk.
    • More severe effects include brain damage with mental retardation, lack of coordination, and inability to move.
    • Eventual blindness, involuntary muscle contractions, seizures, muscle weakness, and inability to speak can occur if there were very toxic levels of mercury during pregnancy.

3. Inorganic mercury:

  • The absorption of ingested mercury salts can be fatal, which is sometimes associated with suicide intent.
  • Mercury salts are very toxic to the kidneys, causing acute tubular necrosis, and nephritic syndrome.
  • Inorganic mercury can pass from a mother’s body into breast milk and into the nursing infant.
  • In all cases, it is very important to remember that the severity of these effects depends on the level of mercury exposure and the length of exposures.


What are specific effects on our health:

Neurological effects:

  • Mercury is very damaging to human health because it is toxic to the nervous system – the brain and spinal cord – is especially dangerous to the developing nervous system of a developing fetus or young child.
  • Methylmercury targets and kills neurons in specific areas of the nervous system including the:
    Visual cortex
    Dorsal root ganglia

  • Adults exposed to too much methylmercury may begin to experience trembling hands and numbness or tingling in their lips, tongues, fingers, or toes. These symptoms may begin long after the mercury exposure.
  • Higher exposures may have an effect on walking, vision, speech and hearing. In particular quantities of exposure, mercury can be fatal.

Neurological effects in the fetus and young children:

  • Greatest risk is in the developing fetus and young children due to the reason that their nervous systems are developing. This makes them four to five times more sensitive to mercury than adults.
  • Methylmercury is especially dangerous to developing fetuses. It can cross the placenta and the blood-brain barrier. The mercury is then concentrated in the brain of the fetus because the metal is absorbed quickly and is not excreted efficiently.
  • Infants who have been exposed 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 because of mercury poisoning show neuron loss in the cerebellum and throughout the cerebral cortex. In addition, mercury also appears to affect brain development by preventing neurons in finding their appropriate areas in the brain.
  • If there is mercury damage before birth or during infancy, they can be delayed in beginning to walk, talk, and may cause lifelong learning difficulties.
  • Developing fetuses can be seriously affected even though the mother shows no symptoms of mercury exposure.


Cases that have shown mercury effects:

  • Mercury effects on developing fetuses have been documented in cases of accidental poisonings and scientific studies.

  • Minamata Bay, Japan
    • In the 1950’s, large amounts of organic mercury were dumped into Minamata Bay in Japan.
    • Mercury-contaminated fish were consumed by pregnant women, causing many children that were born from these women had severe nerve damage, later referred as Fetal Minamata Disease.
  • Iraq
    • In studies of children born to mothers who consumed grain contaminated with organic mercury, the effects showed the children walking at a later age than non-exposed children.

  • Faroe Islands
    • Mercury exposure was caused by contaminated whale meat.
    • Children born to mothers with high body levels of mercury scored lower on brain function tests than mothers with low body levels.


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