Mercury exposure and poisoning

Mercury is a natural substance found in the earth’s crust. It occurs in several forms. Elemental (metallic) mercury is the shiny liquid metal sometimes called “quicksilver.” Inorganic mercury occurs naturally in combination with other elements in mineral ores. Organic mercury, mainly methylmercury, forms when bacteria in water convert other forms of mercury; this is then taken up by fish and passes along the food chain.

Inorganic mercury can be released into the air when coal is burned to generate power, and it is also produced as a waste product in various industrial processes.

For most people, the main source of mercury exposure is methylmercury that has entered the food chain through fish. As a general rule, the larger or older the fish, the higher the level of mercury it tends to contain.

Sources of mercury exposure#

The best way to reduce your risk of mercury poisoning is to prevent or minimise exposure in your environment. Common sources include:

• Fish – larger and older fish species can carry higher levels of mercury, especially if eaten in large quantities.
• Fluorescent lamps and low-energy light bulbs – these contain small amounts of mercury and can release vapour if broken.
• Mercury thermometers – broken “quicksilver” thermometers can release mercury vapour and allow absorption through skin contact.
• Some batteries – can release mercury if broken.
• Amalgam (metal) dental fillings – contain mercury, which can be released when fillings are removed or replaced.

Reducing exposure from fish#

Learn which commercially available and recreationally caught fish are more likely to contain higher levels of mercury. Most people can still eat fish that are higher in mercury, but these should be eaten less often.

Pregnant women, women planning a pregnancy, young children and people with kidney disease should be especially careful and should limit how often they eat high-mercury fish. Follow local food-safety guidance on portion sizes and how often different types of fish can be eaten safely.

Some freshwater fish can have high levels of mercury where past gold mining has increased mercury in riverbeds and sediments. Where this applies, large predatory freshwater fish are most likely to be affected.

Fish oil products and supplements are not a major source of dietary mercury, so there is no need to restrict your intake because of mercury content.

Reducing exposure from light bulbs#

Mercury-containing bulbs include fluorescent tube lamps and compact low-energy bulbs commonly used in homes. The amount of mercury in a single bulb or lamp is very small and unlikely to cause harm. However, care is needed if a bulb or lamp breaks, because this can release mercury vapour. Clean up broken bulbs carefully and follow local guidance on disposal.

Reducing exposure from thermometers and other devices#

Spirit-filled thermometers are now widely available, but some people still use thermometers containing “quicksilver” mercury. Intact, these are not dangerous, but if broken there is a risk of exposure through inhaling mercury vapour and absorbing mercury through the skin. Any spill should be cleaned up immediately and carefully.

Other devices around the home can contain larger amounts of mercury. These include some thermostats and some medical equipment, such as a sphygmomanometer used to measure blood pressure.

Reducing exposure from dental fillings#

Dental fillings treat damaged or worn teeth and can be made of amalgam or of tooth-coloured materials. Amalgam is valued for its strength, especially in the back teeth, which are under a lot of pressure during chewing. Tooth-coloured materials are not as strong as amalgam, but they do not contain mercury.

Older metal amalgam fillings contain higher levels of mercury, and removing or replacing them can release mercury vapour that a patient might inhale. When removing old amalgam fillings, dentists place a protective sheet over the patient’s mouth to catch any fragments before they can be swallowed, and use high-pressure suction to remove most of the solid amalgam and any vapour.

Some people are advised to avoid new amalgam fillings, and to avoid having existing amalgam removed or replaced unless necessary, because:

• mercury can affect the brain and nervous system while these are still growing and developing
• high levels of mercury exposure can affect the kidneys, so exposure should be kept to a minimum.

The best way to avoid needing fillings at all is to take good care of your oral health.

Who is most at risk#

The effect of mercury exposure depends on the type of mercury. In general, mercury tends to affect the nervous system. This means unborn babies and young children are at greater risk, because their nervous systems are still developing.

People at higher risk from mercury exposure include:

• pregnant women – mercury may cross the placenta and enter the bloodstream of the unborn baby
• women who are breastfeeding – small amounts of mercury may pass to the baby through breast milk
• infants and young children
• people with kidney disease

For nursing mothers who have limited their mercury intake before and during pregnancy, the amount of mercury transferred through breast milk will be very low. The benefits of breastfeeding far outweigh any risk from the small amount of mercury that may be present in human milk. Levels of mercury in breast milk are normally not high enough to be a risk for babies.

Pink disease#

In the first half of the twentieth century, teething powders and other baby products sometimes contained mercury, and some babies developed a condition known as pink disease. In this condition the feet, hands and the tip of the nose become bright pink, often with other skin problems, diarrhoea and lethargy.

Pink disease is now rare, but adults who had it as babies tend to be more sensitive to mercury and may have a number of other health complaints.

Symptoms of mercury poisoning#

Health effects from mercury depend on several factors, including the amount and form of mercury, the route and duration of exposure, and age.

Elemental mercury poisoning#

Inhaling mercury vapour can cause acute mercury poisoning. This is most likely after a spill of mercury from a thermometer or other mercury-containing device, especially in places with poor ventilation. Symptoms can include:

• tremors
• headaches
• difficulty sleeping
• impaired sensation
• muscle weakness and twitching
• emotional changes such as mood swings, irritability and nervousness
• kidney damage
• breathing difficulties

Organic (methylmercury) poisoning#

Most people have some methylmercury in their tissues, but at levels that do not pose a risk to health. Excess methylmercury particularly affects the nervous system, which is especially damaging for unborn babies, infants and children whose brains and nervous systems are still developing. Poisoning from methylmercury can take weeks or months to appear, and may cause disturbances in:

• peripheral vision
• sensation, especially in the hands, feet and around the mouth
• coordination and walking
• speech
• hearing

Inorganic mercury poisoning#

This type of poisoning is more often related to industrial exposure. Symptoms can include:

• skin conditions such as rashes and dermatitis
• breathing problems
• mood changes
• problems with memory
• other mental health effects
• reduced muscle strength

Diagnosis and treatment#

Mercury poisoning is diagnosed by testing blood and urine for mercury levels; urine may be collected over a 24-hour period. Your doctor will ask about your possible history of exposure.

Exposure from a chemical spill of elemental or inorganic mercury may produce symptoms more quickly than methylmercury poisoning. If mercury poisoning is suspected, treatment may begin before the diagnosis is confirmed, because test results can take time to come back. In people who are critically ill, doctors will most likely treat with chelation therapy regardless of the form of mercury involved. Chelation therapy uses compounds that enter the bloodstream and bind to mercury so it can be removed by the body.

Cleaning up and disposing of mercury#

For information on how best to recycle or dispose of fluorescent lamps, low-energy light bulbs and mercury-containing batteries used in your home, contact your local waste or environmental authority for guidance, including how to clean up mercury spills safely.

Key points#

• Inhaling mercury vapour can cause acute mercury poisoning.
• Amalgam is used because of its strength, especially in the back teeth that are under a lot of pressure during chewing.
• The benefits of breastfeeding far outweigh any risk from the small amount of mercury that may be present in human milk.
• Unborn babies and children are at greater risk because their nervous systems are still developing.
• Levels of mercury in breast milk are normally not high enough to be a risk for babies.

Where to get help#