Mercury is found in small quantities throughout the environment. It is released by the breakdown of minerals in rocks and soils and as a byproduct of fossil fuel combustion and waste incineration. It is inhaled with the air that we breathe, absorbed through the skin, and ingested with food. The tiny amounts to which the vast majority of people are exposed to do not generally cause health concerns, but people who are exposed to dangerous concentrations of mercury (such as might be found at a hazardous waste site) or are exposed chronically to mercury (such as those who work with heavy metals in their occupation) may have mercury-related symptoms and complications.
Exposure to excessive amounts of mercury can be toxic. The amount of mercury absorbed by an individual and its effects on their health depends on the type of mercury, its concentration, and the exposure time. According to the Agency for Toxic Substances and Disease Registry (ATSDR), very little metallic mercury (less than 0.01%) is absorbed by the body, even if it is swallowed. However, if the same mercury is inhaled as a vapor, about 80% is absorbed into the bloodstream. About 95% of methyl mercury (the type found in fish and other seafood) is absorbed by the gastrointestinal tract. The most common source of human exposure to methyl mercury is as a result of eating contaminated seafood. Fish that come from contaminated waters and larger predator fish fish that have eaten smaller fish may have significantly increased levels of methyl mercury. This is why it is recommended that you know the source of the fish you consume and that you limit the quantity of large predator fish you eat.
Once mercury is absorbed, it finds its way into a variety of body organs, including the kidneys and brain. The body will slowly rid itself of mercury through the urine and stool, but if excessive amounts are present, it can permanently damage the kidneys, nervous system, and brain.
Pregnant women with elevated levels of mercury can pass it on to their fetus, affecting development, especially the fetuss brain, kidneys, and nerves. Mercury can be passed from mother to baby through breast milk during nursing.
How is the sample collected for testing?A blood sample is obtained by inserting a needle into a vein in the arm or a random or 24 hour urine sample may be collected. Rarely, another sample such as hair, breast milk, or nails may be tested.
Is any test preparation needed to ensure the quality of the sample?No test preparation is needed. Consult your doctor or laboratory about urine collection to avoid sample contamination.
How is it used?Mercury testing is done to detect the presence of an excessive amount of mercury. It may be ordered by your doctor to determine whether you have been acutely or chronically exposed to increased levels of mercury. It may also be ordered to monitor those who are exposed to mercury in the workplace.
More than one type of sample may be collected and tested.
- Blood is primarily tested to detect the presence of methyl mercury. Other forms of mercury can also be detected in the blood, but according to the Agency for Toxic Substances and Disease Registry (ATSDR), the amount present will decrease by half about every 3 days as the mercury moves into other organs.
- Urine is used to test for metallic mercury and inorganic forms of mercury, but it cannot be used to determine exposure to methyl mercury.
- Hair testing may be useful to detect methyl mercury exposures that occurred several months previously, but hair testing is relatively complex and is not used frequently.
- Although not routinely ordered tests, mercury has been shown to be present in nails, breast milk, stool, and breath.
When is it ordered?Mercury testing may be ordered when a patient has symptoms suggesting excessive exposure to mercury. Acute symptoms may include:
- burning in the mouth and lungs
- cough, difficulty breathing, chest tightness
- decreased urine output
- nausea, vomiting, diarrhea
- increased heart rate
Those who are chronically exposed may have nonspecific symptoms that involve the lungs, kidneys, and nervous system. Some of the chronic symptoms may include:
- problems with hearing, taste and smell
- blurry vision or sometimes tunnel vision
- tingling or tremors in the arms or legs
- difficulty walking
Testing may also be ordered when a patient is known to have been exposed to mercury to help evaluate the extent of the exposure. Mercury measurements may be ordered regularly as a monitoring tool for those patients who work in industries that utilize mercury and may be ordered, along with lead and/or other heavy metals, for individuals who work with a variety of potentially hazardous materials.
What does the test result mean?Normal levels of mercury in blood and urine indicate that it is likely that the patient has not been exposed to excessive levels of mercury, at least not in the window of time that the test is measuring.
Elevated levels of mercury in blood or urine indicate that excessive exposure to mercury has occurred. However, it does not indicate the form or quantity of mercury to which a person was exposed. Increased blood levels suggest a relatively recent exposure to mercury, while a 24-hour urine sample gives more of an average past history of exposure to metallic or inorganic mercury.
Increased levels of mercury in hair testing may indicate exposure to increased levels of methyl mercury, but hair samples are rarely used because of issues involving testing standardization, sample contamination, and the fact that hair is subject to many pre-analytical variables (hair exposure to dyes, bleach, shampoo, etc.).
Mercury is considered to be a non-essential trace element in humans; therefore, low levels of mercury are usually not of any concern.
Is there anything else I should know?Measures have been taken in recent years to reduce and control the publics exposure to mercury. Stricter regulations and recommendations have lowered the amounts allowable in the air, water, soil, food, and in the workplace.
The high levels of mercury found in certain fish may harm the developing nervous systems in unborn babies and young children. The FDA recommends that pregnant women, women who may become pregnant, young children, and nursing mothers avoid eating shark, swordfish, king mackerel and tilefish. It advises these groups to eat fish that are usually found to have lower levels of mercury such as canned light tuna, shrimp, or salmon.
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Do silver teeth fillings contain mercury?Yes. Dental amalgams (teeth fillings) are made up of about 50% metallic mercury. Some people feel that the tiny amount of mercury vapor released when a person chews may affect their health, but internationally most major health organizations feel that the amalgams are safe at this time. A few countries have begun to restrict their use as a precaution.