What is being tested?

Mercury is an element that exists in three forms: as a free metallic (liquid or vapour), an inorganic compound (mercury salt), and as a variety of organic compounds (methyl mercury). It has no known function in normal metabolism but is able to bind to a number of proteins, interfering with their function.

Mercury has been used in medicine for centuries and may be 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. Microorganisms that live in marine and freshwater sediments methylate mercury and this methyl mercury is concentrated up the food chain and can be present in higher concentrations in top predators such as swordfish or tuna.

Metallic mercury is readily absorbed by inhalation whereas little is absorbed after ingestion. Inorganic compounds are also poorly absorbed from the gut. Organic mercury compounds are absorbed very well from either the lungs or the gut. Phenyl mercuric compounds (used in fungicides) may be absorbed through the skin. Organic mercury is excreted in bile, while inorganic and metallic mercury are excreted via urine.

The small amounts of mercury the general population are exposed to do not generally cause health concerns but people who are exposed to dangerous concentrations or are exposed chronically to mercury (such as those who work with 'heavy metals' in their occupation) may have mercury-related symptoms and complications.

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.

Once mercury is absorbed, it is distributed throughout the body, with the majority accumulating in the kidneys and brain. Mercury has a biological half-life of about 60 days, with most being excreted in the urine.

Pregnant women with elevated levels of mercury can pass it on to their foetus, affecting development especially the foetus's brain, kidneys, and nerves. Mercury can be passed from mother to baby through breast milk during nursing.

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 the primary sample used to detect the presence of methyl mercury. 
• Urine is the primary sample used to detect the presence of metallic mercury and inorganic forms of mercury, but it is not the best specimen to determine exposure to methyl mercury.
• Although not routinely ordered tests, mercury has been shown to be present in hair, nails, breast milk, stool and breath.

When is it requested?

Mercury testing may be ordered when a patient has symptoms suggesting excessive exposure to mercury. Low grade continuous exposure can lead to:

• Inflammation of the mouth, soft gums, loose teeth, excessive salivation, metallic taste and foul breath
• Tremor (hatters shakes)
• Mental and nervous symptoms including behavioural changes, stammering, anxiety, loss of sleep and loss of energy
• Renal impairment
• A possible increase in hypertension and cardio vascular disease

Symptoms due to acute exposure will depend on the means of the exposure.

• Exposure to mercury vapour will cause flu like symptomes, progressing to pulmonary oedema
• Gastrointestinal exposure can cause gastroenteritis symptoms

Mercury measurements may be ordered regularly as a monitoring tool for those patients who work in industries that utilise mercury and may be ordered, along with lead and/or other heavy metals, for individuals who work with a variety of potentially hazardous materials.

Mercury toxicity is related to the method of exposure and the type of mercurial involved. Inorganic mercury that may be ingested is essentially non-toxic. Inorganic mercury that is inhaled is a lung toxin.

What does the 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. But 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 standardisation, sample contamination and the fact that hair is subject to many factors (hair exposure to dyes, bleach, shampoo, etc.) which may affect the amount of mercury present in the hair.

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?

Intramuscular BAL (British anti-Lewisite or dimercaprol) has been used to treat inorganic mercury poisoning. Its use is contraindicated in methyl mercury poisoning. Dimercaptosuccinic acid is a new drug that shows promise for the treatment of mercury exposures of all types.

The high levels of mercury found in certain fish may harm the developing nervous systems in unborn babies and young children. Food Standards Australia New Zealand (FSANZ) recommend that pregnant women, women who may become pregnant, young children and nursing mothers restrict their intake of certain fish. The Better Health Channel advises these groups to eat fish that are usually found to have lower levels of mercury such as canned light tuna, prawns, lobsters, oysters or salmon.

Common questions

• What is thimerosal?

Thiomersal (or thimerosal) is a preservative that contains a form of mercury. It was used in very small amounts in vaccines from the 1930s onwards, to prevent contamination of vaccines. None of the vaccines on the National Immunisation Program for children under five years of age contain thiomersal (it has not been used as a preservative in Australian routine childhood vaccinations since 2000).

• 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 vapour released when a person chews may affect their health, but in Australia the Australian Dental Association reports that the amalgams are safe at this time. Improper removal of amalgam fillings may increase risk of mercury exposure. A few countries have begun to restrict their use as a precaution.

More information

RCPA Manual: Mercury - urine