Mercury
Your Health and the Environment

Health Concerns

In this section, health concerns resulting from mercury exposure in adults, pregnant women and children are discussed. Exposure to mercury mostly affects the nervous system, the cardiovascular system, the immune system, and the kidneys. Fetal mercury exposure can lead to neurodevelopmental problems in children.

The health effects of mercury in its various forms are well documented. For further consultation, the public health statement for mercury produced by the Agency for Toxic Substances and Disease Registry is available at the following site (PDF Version - 151 K):
http://www.atsdr.cdc.gov/toxprofiles/tp46-c1.pdf

Q35. What happens to elemental mercury in the body and where does it accumulate?

• Elemental mercury can enter the body by absorption through the skin, by absorption through the stomach if swallowed, or by inhalation. Absorption depends on the route of exposure (inhalation, ingestion or dermal).
• When mercury vapour is inhaled, the lung is the main site of absorption. Approximately 80% of the inhaled vapour enters the bloodstream and is rapidly transported to other parts of the body, including the brain and kidneys. It readily crosses the blood-brain and placental barriers. Elemental mercury, in the blood of pregnant women, may be passed on to the developing fetus.
• If small amounts of metallic mercury are ingested from a broken oral thermometer, less than 0.01% of the mercury will be absorbed by the body through the stomach or intestine. A condition such as a bleeding ulcer in the gastrointestinal tract can increase the rate of absorption into the bloodstream.
• Once in the body, elemental mercury can stay there for weeks or months. Most of it will accumulate in the kidneys and, to a lesser extent, in the brain, where it is readily converted to an inorganic form and remains there for a long time. More mercury is deposited in the brain after exposure to elemental mercury than after exposure to inorganic mercury compounds.

Q36. What happens to inorganic mercury in the body and where does it accumulate?

• Inorganic mercury salts or compounds do not generally vaporize at room temperatures and, upon inhalation, these compounds are not as likely to enter your body as easily as inhaled metallic mercury vapour.
• When inorganic mercury compounds are ingested, generally less than 10% is absorbed through the intestinal tract; however, under certain conditions, such as bleeding ulcers, up to 40% can be absorbed into the body through the lesion in the stomach and/or intestines.
• Smaller amounts of inorganic mercury can be absorbed through the skin, but ingestion is the main pathway into the body.
• Absorbed inorganic mercury accumulates mostly in the kidneys and does not cross placental or blood-brain barriers as easily as elemental or methyl mercury. It is, however, accumulated in placental tissues.
• In a nursing mother, some of the inorganic mercury from her body will be passed on to her child through her breast milk.

Q37. What happens to methyl mercury in the body and where does it accumulate?

• When fish or other foods contaminated with methyl mercury are consumed, approximately 95% of the methyl mercury is absorbed through the stomach and intestinal tract, then transferred to the blood stream and distributed throughout the body.
• Only small amounts of methyl mercury can be absorbed into the bloodstream directly through the skin, but other forms of organic mercury (in particular dimethyl mercury) can rapidly enter the body through skin.
• It readily passes the blood-brain barrier and enters the brain.
• In pregnant women, methyl mercury easily crosses the placental barrier and moves into the blood of the developing child and subsequently into the child's brain and other tissues. As with inorganic mercury, some of the methyl mercury in a nursing woman's body will mobilize into her breast milk.
• Methyl mercury can be changed, within the body, into inorganic mercury. When this happens in the brain, mercury can remain there for a long time.

Q38. How long does it take to excrete mercury (all forms) from the body?

• The majority of inorganic and elemental mercury compounds exit the body in the urine and faeces over a period of several weeks to months; smaller amounts of absorbed mercury vapours exit the body in exhaled breath and through perspiration, more rapidly.
• The half-life in the whole body has been observed to be within the range of 29 to 60 days, with an average of 42 days for inorganic mercury.
• Methyl mercury leaves slowly over a period of several months, mostly as inorganic mercury in faeces. After stopping exposure to methyl mercury, it takes between 45 and 70 days to decrease methyl mercury concentrations by half in a person's blood and slightly longer in the whole body.

Q39. What are the health effects and symptoms of inorganic mercury exposure in adults?

• Acute poisoning following exposure to mercury vapours at high levels (over 1 milligram per cubic meter) for a short period, may cause severe irritation of the airways, pneumonitis, pulmonary edema and other symptoms of lung damage. It can damage the brain, nerves, kidneys and lungs and, in extreme cases, may cause coma or death. Some people have experienced tremors, difficulty in coordinating the movement of their feet or hands, problems with balance, and a numbness or prickly sensation in their fingers.
• Following chronic exposure to low levels of mercury vapour (50 to 100 microgram per cubic meter), it may take some time to cause adverse effects on the central nervous system, kidney and thyroid, and the effects could be more subtle. It is difficult to distinguish mercury symptoms from some other common ailments. Symptoms include tremors (shaking), muscular weakness, depression, personality changes and short-term memory loss in adults, and skin rashes, particularly redness and peeling of the hands and feet, in children.
• Acute poisoning from inorganic mercury salts is rare, except in cases of accidental ingestion. The kidney is the primary target organ. Chronic occupational exposure to mercury salts has been associated with effects on the central nervous system similar to those associated with exposure to elemental mercury vapour.

Q40. What are the health effects and symptoms of methyl mercury exposure in adults?
A wide range of adverse health effects have been observed in adults following methyl mercury exposure, the severity depending largely upon the magnitude of the dose and the duration of exposure.

• Devastating neurological damage, and death occurred after the extremely high exposures stemming from the poisoning episodes in Minamata, Japan and in Iraq. Methyl mercury may also cause adverse effects on other organs in the body.
• Effects noted at the earliest stages of exposure include paresthesia (numbness or "pins and needles" sensation) in the extremities of the hands and feet, malaise or blurred vision. This may progress to ataxia (loss of the ability to coordinate muscular movement), dysarthria (speech difficulties) or loss of hearing and constriction of visual fields.
• Methyl mercury poisoning is characterized by a latent period between exposure and onset of symptoms. The latent period can vary from one to several months, depending on the dose and duration of the exposure.
• In Nunavik, mercury exposure is chronic (exposure at low doses over a long period of time) and, so far, no cases with these symptoms have been reported. Nutritional benefits of selenium and omega-3 fatty acid, both commonly found in fish and/or marine mammals, might counteract the adverse effects of methylmercury to some degree.

Q41. What type of treatment exists to remove mercury from blood?
If the level of mercury detected in the blood or urine is considered high, a doctor might prescribe chelating agents that bind mercury ions. The mercury and the chelating agent are then excreted from the body together. If no chelating agent is used, mercury can still be excreted by the body, but not as quickly. The excretion half-life (time for the amount of mercury to be reduced by half in the body) for metallic mercury is 33.1 days. A number of chelating agents that bind to the mercury are available and can increase the excretion rate up to threefold. As with any medicine, chelating agents can cause side effects.

Q42. Should I be concerned about mercury concentrations in drinking water?
Mercury levels in Canadian drinking water are generally well below the established maximum acceptable concentration (MAC) of 0.001 milligram per litre (Health Canada, Guidelines for Drinking Water Quality). While mercury levels may be elevated in certain source waters, because of natural mercury deposits or pollution, exposure via drinking water is not generally a concern. In those situations where mercury levels are deemed to be too high, effective treatment technologies exist for private and municipal water supplies.