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Mercury poisoning definition and facts*

*Mercury poisoning facts by John P. Cunha, DO, FACOEP

  • Mercury is a naturally occurring element found in air, water and soil. A highly toxic form (methylmercury) builds up in fish, shellfish and animals that eat fish. Fish and shellfish are the main sources of methylmercury exposure to humans.
    • Fish that typically have higher levels of mercury include king mackerel, marlin, orange roughy, shark, swordfish, tilefish, and ahi and bigeye tuna. Many of these types of fish are used in sushi.
  • Other sources of mercury can be silver-colored dental fillings that contain up to 50% mercury by weight and can release mercury vapor, fluorescent light bulbs that use electricity to excite mercury vapor, and mercury fever thermometers made of glass.
  • Mercury exists in several forms: elemental or metallic mercury, inorganic mercury compounds, and organic mercury compounds.
  • Mercury exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system. High levels of methylmercury in the bloodstream of unborn babies and young children may harm the developing nervous system, making the child less able to think and learn.
  • Signs and symptoms of methylmercury poisoning may include:
    • Impairment of peripheral vision
    • Disturbances in sensations ("pins and needles" feelings)
    • Lack of coordination
    • Impairment of speech, hearing, walking
    • Muscle weakness
  • Elemental (metallic) mercury primarily causes health effects when it is breathed as a vapor where it can be absorbed through the lungs.
  • Signs and symptoms of acute elemental (metallic) mercury poisoning include:
    • Tremors
    • Emotional changes
    • Insomnia
    • Weakness
    • Muscle atrophy
    • Twitching
    • Headaches
    • Disturbances in sensations
    • Changes in nerve responses
    • Performance deficits on tests of cognitive function.
  • Higher exposures may result in kidney effects, respiratory failure and death.
  • Consult your doctor if you believe you have been exposed to mercury. Testing for mercury may involve tests on the hair, blood, and urine. Treatment for mercury toxicity includes removal of the source of mercury exposure, supportive care, and chelation therapy to help remove the metals from the body.
  • Recycling of mercury-containing products is one of the best ways to help prevent mercury releases to the environment by keeping these products out of landfills and incinerators.

What is mercury?

Mercury is a naturally occurring element. It is contained in some of the fish we eat, whether caught in local lakes and streams or bought in a grocery store. Mercury is also contained in some of the products we use, which may be found in your home, at the dentist, and at schools. This article provides links to information about sources of mercury exposure, potential health effects, fish that may contain mercury, consumer products that contain mercury, and ways to reduce your exposure to mercury.

What are the forms sources of mercury?

Forms of mercury. Mercury is a naturally occurring element that is found in air, water and soil. It exists in three chemical forms. They each have specific effects on human health.

  • Methylmercury
  • Elemental mercury
  • Other mercury compounds (inorganic and organic)

Sources of mercury. Mercury is an element in the earth's crust. Humans cannot create or destroy mercury. Pure mercury is a liquid metal, sometimes referred to as quicksilver that volatizes readily. It has traditionally been used to make products like thermometers, switches, and some light bulbs.

Mercury is found in many rocks including coal. When coal is burned, mercury is released into the environment. Coal-burning power plants are the largest human-caused source of mercury emissions to the air in the United States, accounting for over 40 percent of all domestic human-caused mercury emissions. EPA has estimated that about one quarter of U.S. emissions from coal-burning power plants are deposited within the contiguous U.S. and the remainder enters the global cycle. Burning hazardous wastes, producing chlorine, breaking mercury products, and spilling mercury, as well as the improper treatment and disposal of products or wastes containing mercury, can also release it into the environment. Current estimates are that less than half of all mercury deposition within the U.S. comes from U.S. sources.

Exposure to mercury. Mercury in the air eventually settles into water or onto land where it can be washed into water. Once deposited, certain microorganisms can change it into methylmercury, a highly toxic form that builds up in fish, shellfish and animals that eat fish. Fish and shellfish are the main sources of methylmercury exposure to humans. Methylmercury builds up more in some types of fish and shellfish than others.

Fish that typically have higher levels of mercury include

  • king mackerel,
  • marlin,
  • orange roughy,
  • shark, swordfish,
  • tilefish, and
  • and bigeye tuna.

Many of these types of fish are used in sushi. White albacore canned tuna typically has three times as much mercury as chunk light canned tuna. The levels of methylmercury in fish and shellfish depend on what they eat, how long they live and how high they are in the food chain.

EPA works with the U.S. Food and Drug Administration (FDA) and with states and tribes to issue advice to women who may become pregnant, pregnant women, nursing mothers, and parents of young children about how often they should eat certain types of commercially-caught fish and shellfish. Fish advisories are also issued for men, women, and children of all ages when appropriate. In addition, EPA releases an annual summary of information on locally-issued fish advisories and safe-eating guidelines to the public. Fish is a beneficial part of the diet, so EPA & FDA encourage people to continue to eat fish that are low in methylmercury.

Another less common exposure to mercury that can be a concern is breathing mercury vapor. These exposures can occur when elemental mercury or products that contain elemental mercury break and release mercury to the air, particularly in warm or poorly-ventilated indoor spaces.

Health effects of mercury. Mercury exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages. Research shows that most people's fish consumption does not cause a health concern. However, it has been demonstrated that high levels of methylmercury in the bloodstream of unborn babies and young children may harm the developing nervous system, making the child less able to think and learn.

Ecological effects of mercury. Birds and mammals that eat fish are more exposed to mercury than other animals in water ecosystems. Similarly, predators that eat fish-eating animals may be highly exposed. At high levels of exposure, methylmercury's harmful effects on these animals include death, reduced reproduction, slower growth and development, and abnormal behavior.

Reducing mercury releases. EPA issues regulations that require industry to reduce mercury releases to air and water and to properly treat and dispose of mercury wastes. EPA also works with industry to promote voluntary reductions in mercury use and releases, and with partners in state, local and tribal governments to improve their mercury reduction programs. EPA works with international organizations to prevent the release of mercury in other countries. The public can contribute to mercury reduction efforts by purchasing mercury-free products and correctly disposing of products that contain mercury by reducing demand for products whose production leads to the release of mercury into the environment.

What factors determine the severity of health effects from mercury exposure?

People in the U.S. are mainly exposed to methylmercury, an organic compound, when they eat fish and shellfish that contain methylmercury. Whether an exposure to the various forms of mercury will harm a person's health depends on a number of factors. Almost all people have at least trace amounts of methylmercury in their tissues, reflecting methylmercury's widespread presence in the environment and people's exposure through the consumption of fish and shellfish. People may be exposed to mercury in any of its forms under different circumstances. The factors that determine how severe the health effects are from mercury exposure include these

  • the chemical form of mercury;
  • the dose;
  • the age of the person exposed (the fetus is the most susceptible);
  • the duration of exposure;
  • the route of exposure -- inhalation, ingestion, dermal contact, etc.; and
  • the health of the person exposed.

What are the side effects, signs, and symptoms of mercury poisoning?

What are the side effects methylmercury poisoning in fetus' and humans?

For fetuses, infants, and children, the primary health effect of methylmercury is impaired neurological development. Methylmercury exposure in the womb, which can result from a mother's consumption of fish and shellfish that contain methylmercury, can adversely affect a baby's growing brain and nervous system. Impacts on cognitive thinking, memory, attention, language, and fine motor and visual spatial skills have been seen in children exposed to methylmercury in the womb. Recent human biological monitoring by the Centers for Disease Control and Prevention in 1999 and 2000 (PDF) shows that most people have blood mercury levels below a level associated with possible health effects. More recent data from the CDC support this general finding.

Outbreaks of methylmercury poisonings have made it clear that adults, children, and developing fetuses are at risk from ingestion exposure to methylmercury. During these poisoning outbreaks some mothers with no symptoms of nervous system damage gave birth to infants with severe disabilities, it became clear that the developing nervous system of the fetus may be more vulnerable to methylmercury than is the adult nervous system.

For more information on fish consumption advisories across the country, visit EPA's fish consumption web pages.

What are the signs and symptoms of methylmercury poisoning?

In addition to the subtle impairments noted above, symptoms of methylmercury poisoning may include;

  • impairment of the peripheral vision;
  • disturbances in sensations ("pins and needles" feelings, usually in the hands, feet, and around the mouth);
  • lack of coordination of movements;
  • impairment of speech, hearing, walking; and
  • muscle weakness.

People concerned about their exposure to methylmercury should consult their physician.

What are the side effects of elemental mercury?

Elemental (metallic) mercury primarily causes health effects when it is breathed as a vapor where it can be absorbed through the lungs. These exposures can occur when elemental mercury is spilled or products that contain elemental mercury break and expose mercury to the air, particularly in warm or poorly-ventilated indoor spaces.

What are the signs and symptoms of elemental mercury?

Symptoms include these:

  • tremors;
  • emotional changes (for example, mood swings, irritability, nervousness, excessive shyness);
  • insomnia;
  • neuromuscular changes (such as weakness, muscle atrophy, twitching);
  • headaches;
  • disturbances in sensations;
  • changes in nerve responses;
  • performance deficits on tests of cognitive function.

At higher exposures there may be kidney effects, respiratory failure and death. People concerned about their exposure to elemental mercury should consult their physician.

What are the side effects of other mercury compounds (inorganic and organic)?

High exposures to inorganic mercury may result in damage to the gastrointestinal tract, the nervous system, and the kidneys. Both inorganic and organic mercury compounds are absorbed through the gastrointestinal tract and affect other systems via this route. However, organic mercury compounds are more readily absorbed via ingestion than inorganic mercury compounds.

What are the signs and symptoms of high exposures to inorganic mercury?

Symptoms of high exposures to inorganic mercury include:

People concerned about their exposure to inorganic mercury should consult their physician.

What about mercury in batteries?

Most batteries made in the U.S. do not contain added mercury. The two exceptions are mercuric oxide batteries and button cell batteries. Mercuric oxide batteries are produced for specialized use in military and medical equipment where a stable current and long service life is essential. Button cell batteries are miniature batteries in the shape of a coin or button that are used to provide power for a large variety of small portable electronic devices.

The use and disposal of mercury-added button cells are unregulated at the federal level.

  • They do not have to be labeled;
  • it is legal to dispose of them in the household trash; and
  • they rarely are collected for recycling in most U.S. jurisdictions.

Some states are now considering whether the disposal of button cell batteries should be regulated or whether recycling should be encouraged. Because button batteries currently are not widely targeted for recycling, almost all of this mercury presumably ends up in the municipal solid waste stream where it is either incinerated or landfilled.

For a more information on batteries, see EPA's Web page on Consumer and Commercial Products.

What about mercury in dental amalgam?

The silver fillings used by dentists to restore teeth are composed of a metal "amalgam" containing roughly 50% elemental mercury and 50% other metals (mostly silver with some tin and copper). Amalgam is one of the most commonly used tooth fillings, and is considered to be a safe, sound, and effective treatment for tooth decay. Amalgam has been the most widely used tooth filling material for decades. It remains popular because it is strong, lasting and low-cost. Dental amalgams are considered medical devices and are regulated by the U.S. Food and Drug Administration (FDA).

Safety of Dental Amalgam Fillings

The mercury found in amalgam fillings has raised some safety concerns over the years. Amalgam can release small amounts of mercury vapor over time, and patients can absorb these vapors by inhaling or ingesting them.

According to the Centers for Disease Control and Prevention (CDC), there is little scientific evidence that the health of the vast majority of people with dental amalgam is compromised, nor that removing amalgam fillings has a beneficial effect on health. A 2004 review of the scientific literature conducted for the U.S. Public Health Service found "insufficient evidence of a link between dental mercury and health problems, except in rare instances of allergic reaction."

The Food and Drug Administration (FDA) consumer update on dental amalgam advises, as a precaution, that pregnant women and persons who may have a health condition that makes them more sensitive to mercury exposure should discuss dental treatment options with their health care practitioner. FDA, which regulates the use of dental amalgam, is reviewing the scientific evidence on the safe use of amalgam.

Alternatives to Dental Amalgam Fillings

Amalgam use is declining because the incidence of dental decay is decreasing and because improved substitute materials are now available for certain applications. If dental patients do not want to use mercury amalgam, there are several non-mercury restorative materials available. Presently, there are six types of restorative materials:

  1. mercury amalgam,
  2. resin composite,
  3. glass ionomer,
  4. resin ionomer,
  5. porcelain, and
  6. gold alloys.

Each type of restorative material has advantages and disadvantages. Some factors that influence the choice of restorative material used include: cost, strength, durability, location of cavity, and aesthetics.

The choice of dental treatment rests with dental professionals and their patients, so you should talk with your dentist about dental treatment options that are available. The American Dental Association provides a brochure for dental patients on the advantages and disadvantages of various types of dental fillings.

Environmental Releases of Mercury from Dental Amalgam Waste

Mercury from dental amalgam is a major source of controllable mercury released to the environment and likely will remain a significant concern into the future.

Mercury from dental amalgam is released to the environment through three primary pathways:

  1. in wastewater,
  2. as solid waste, and
  3. through cremation of bodies containing dental amalgam.

The majority of dental mercury amalgam is discharged from dental offices to wastewater treatment systems. For more information on environmental releases of mercury from dental amalgam, see EPA's mercury Web page on Consumer and Commercial Products.

What about mercury in fish?

Fish and shellfish are an important part of a healthy diet. Fish and shellfish contain high-quality protein and other essential nutrients, are low in saturated fat, and contain omega-3 fatty acids. A well-balanced diet that includes a variety of fish and shellfish can contribute to heart health and children's proper growth and development.

However, nearly all fish and shellfish contain traces of methylmercury. For most people, the risk from exposure to methylmercury by eating fish and shellfish is not a health concern. Yet some fish and shellfish contain higher levels of mercury that may harm an unborn baby or young child's developing nervous system. The risks from methlymercury in fish and shellfish depend on the amount of fish and shellfish eaten and the levels of methylmercury in the fish. Federal, state and local governments issue fish advisories when the fish are unsafe to eat.

Fish Consumption Advisories - This page provides links to extensive information on fish advisories, including advisories issued by state and local governments and by the EPA and the U.S. Food and Drug Administration.

Fish Kids - This Web site uses interactive stories and games to teach kids ages 8-12 about contaminants in fish and fish advisories.

What about mercury in fluorescent light bulbs?

A fluorescent light bulb (also referred to as a "lamp") is a gas-discharge bulb that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that causes a phosphor to fluoresce, producing visible light. Mercury is an essential component of all fluorescent light bulbs, and allows these bulbs to be energy-efficient light sources.

Types of Fluorescent Bulbs

Tube: The standard straight "linear" tube comes in a variety of diameters and lengths. For example:

  • The T-4 is ½ inch in diameter and often used under kitchen cabinets.
  • The T-8 is 1 inch in diameter and the T-12 is 1½ inches in diameter.
  • Variations include the "U-tube" bent in half to form a U-shape, and the "circline" tube bent into a circle.
  • The larger-diameter tube fluorescents are used in ceiling light fixtures.

Compact fluorescent light (CFL): This is a short bulb made of a tube about the diameter of a pencil that has been either folded or twisted, resulting in an overall size that rivals a standard incandescent light bulb. Since the CFL fits into a standard light socket, the bulb and fixture design possibilities are vastly increased over that of a fluorescent tube. CFLs are now available in a variety of shapes, including spiral (twisted), short tube (folded over) and globe. A globe CFL is either round or A-shaped glass that contains within it a spiral or folded tube.

EPA encourages Americans to use compact fluorescent lights in order to save energy. Switching from traditional incandescent bulbs to CFLs is an effective, simple change everyone can make right now to help use less electricity at home and prevent greenhouse gas emissions that lead to global climate change.

Learn about CFLs – General information on Energy Star-qualified compact fluorescent light bulbs (CFLs), where to use CFLs in a home, and how to choose the right type of CFL bulb.

CFLs contain a very small amount of mercury sealed within the glass tubing. No mercury is released when the bulbs are intact (not broken) or in use, but CFLs can break and release mercury vapor if dropped or roughly handled. EPA encourages consumers to handle and use CFLs safely. Be careful when removing the bulb from its packaging, installing it, or replacing it. More information is provided in the Energy Star fact sheet: CFLs and Mercury (PDF).

If a CFL breaks in your home, please follow EPA's recommended steps to carefully clean up and dispose of broken bulbs. These recommendations will help to minimize any exposure to released mercury vapor.

EPA encourages the recycling of burned out fluorescent bulbs rather than disposing of them in regular household trash. Recycling of burned out CFLs is one of the best ways to help prevent the release of mercury to the environment by keeping mercury out of landfills and incinerators. Recycling of these bulbs also allows the reuse of the glass, metals and other materials that make up fluorescent lights.

What about thimerosal in vaccines?

Some consumers are concerned about the use of thimerosal, a mercury-containing preservative, in vaccines. Since 2001, with the exception of some influenza vaccines (flu), thimerosal is not used as a preservative in routinely recommended childhood vaccines.

To learn more about this use of thimerosal, please see information from the Food and Drug Administration (FDA) on medicines that contain mercury and thimerosal in vaccines, and information from the Centers for Disease Control and Prevention on thimerosal in vaccines.

Thermometers (Fever)

Mercury fever thermometers are made of glass the size of a straw, with a silvery-white liquid inside, and used to be a common item in many households, schools and medical facilities. Now it is nearly impossible to buy one as digital thermometers have become the norm. There are two general types of mercury thermometers that measure body temperature: (1) oral/rectal/baby thermometers, containing about 0.61 grams of mercury; and (2) basal temperature thermometers, containing about 2.25 grams of mercury.

The presence of a mercury thermometer itself is not a problem. However glass thermometers may break while in use, releasing harmful mercury vapor and exposing people in the immediate indoor area. Mercury thermometers are also likely to break after being discarded in regular trash, resulting in mercury releases in the landfill or trash incinerator, or during transportation to either location. It is for this reason The American Academy of Pediatrics (AAP) encourages parents to remove mercury thermometers from their homes to prevent accidental exposure and poisoning.

Restrictions on Sales of Mercury Fever Thermometers

In order to help remove the threat of mercury fever thermometer breakage and subsequent release of mercury vapor indoors, some states and municipalities have passed laws or ordinances prohibiting the manufacture, sale and/or distribution of these thermometers. As of October 2, 2008, thirteen states have laws that limit the manufacture, sale and/or distribution of mercury fever thermometers:

  1. California,
  2. Connecticut,
  3. Illinois,
  4. Indiana,
  5. Maine,
  6. Maryland,
  7. Massachusetts,
  8. Michigan,
  9. Minnesota,
  10. New Hampshire,
  11. Rhode Island,
  12. Oregon,
  13. Washington.

The Health Care Without Harm Web site presents information on specific state laws and municipal ordinances.

Alternatives: Mercury-free Fever Thermometers

A variety of accurate and reliable mercury-free fever thermometers are available at your local pharmacy. Alternatives most comparable in cost and use to the mercury fever thermometer include battery and solar powered digital thermometers. These can all be used orally, rectally, or in the armpit. You should choose a thermometer that is easy to use and read.

If choosing a battery powered digital thermometer, choose one that contains a replaceable battery; some are not replaceable. The battery is a button cell battery and may contain a small amount of mercury, so it should be recycled through a local battery collection program or household hazardous waste collection center. Consult your local or state collection program regarding where batteries should be taken.

What To Do If a Mercury Fever Thermometer Breaks

A broken mercury thermometer is a serious health threat. If mercury spills out of a broken thermometer and is not cleaned up, it will evaporate into invisible vapor, potentially reaching dangerous levels in indoor air. If a thermometer breaks in your home, please follow EPA's recommended cleanup steps to carefully clean up and dispose of the broken glass and silver mercury beads. These recommendations will help minimize any exposure to released mercury vapor.

Disposal of Old Mercury Fever Thermometers

EPA encourages the recycling of mercury fever thermometers rather than disposing of them in regular household trash. Recycling is one of the best ways to help prevent the release of mercury to the environment by keeping mercury out of landfills and trash incinerators.

Many states and local agencies have developed collection/exchange programs for mercury-containing devices such as thermometers. Some counties and cities also have household hazardous waste collection programs. For information about these programs, contact your local officials to find out when and where a collection will be held in your area.

Recycling and Disposal

EPA encourages the recycling of mercury-containing products rather than disposing of them in regular household trash. Recycling of mercury-containing products is one of the best ways to help prevent mercury releases to the environment by keeping these products out of landfills and incinerators.

Some localities have collection/exchange programs for mercury-containing devices, such as thermometers, manometers, and thermostats, and recycling programs for fluorescent light bulbs. Some counties and cities also have household hazardous waste collection programs. For information about these programs, contact your local officials to find out when and where a collection will be held in your area.

Spills and Cleanup

Mercury is used in a variety of consumer products such as thermometers and fluorescent bulbs. If you accidentally break a mercury-containing product during use, or improperly dispose of such products, they will release mercury vapors that are harmful to human and ecological health.

Spills - Information on what to do, and what never to do, if you spill mercury.

Mercury-Containing Products

Elemental mercury has properties that have led to its use in many different products and industrial sectors. While some manufacturers have reduced or eliminated their use of mercury in products, there are still many consumer items in the marketplace that contain mercury. EPA encourages individuals, organizations and businesses to use non-mercury alternatives and to recycle unused mercury-containing products whenever possible.

Consumer and Commercial Products - This Web page provides more extensive information on mercury-containing products, plus links to related information from other federal agencies, state environmental agencies, and non-governmental organizations.

EPA's Database on Mercury-Containing Products and Alternatives - This searchable database contains publicly available information on consumer and commercial products that contain mercury, and also information on non-mercury alternatives. This is a Windows database designed to be downloaded to operate on an individual computer. The primary source of information on mercury-containing products is the IMERC Mercury-added Products Database, which is discussed below. EPA supplements the IMERC data with publicly available information on additional mercury-containing products. Information on non-mercury alternatives is gathered from a variety of public sources, including industry associations, non-governmental organizations, numerous Web sites and published reports. The information is updated annually.

Interstate Mercury Education & Reduction Clearinghouse (IMERC) Mercury-Added Products Database - The IMERC database is managed by the Northeast Waste Management Officials' Association (NEWMOA). It presents information on: (1) the amount and purpose of mercury in specific products that are sold in eight IMERC-member states; (2) the total amount of mercury in these products sold nationally in a given year; and (3) the manufacturers of these products. The information is submitted to IMERC by or on behalf of product manufacturers in compliance with laws in the eight states of Connecticut, Louisiana, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont. Notification requirements have been in effect for products manufactured or distributed in these states beginning in January 2001. The information is updated every three years.

Where You Live

Where you live - Mercury can be found almost anywhere. On this page, you will find a list of links to information about mercury in your home, community, state, region, and the world.

REFERENCES:

American Academy of Pediatrics. "How to Take a Child's Temperature." Nov 21, 2015.
<https://www.healthychildren.org/English/health-issues/conditions/fever/Pages/How-to-Take-a-Childs-Temperature.aspx>

Environmental Defense Fund. Mercury alert: Is canned tuna safe to eat?
<https://www.edf.org/oceans/mercury-alert-canned-tuna-safe-eat>

Menon, Shanti. "Mercury Guide." Natural Resources Defense Council. Updated: Mar 10, 2016.
<https://www.nrdc.org/stories/mercury-guide>

Olson, D.A., MD. "Mercury Toxicity Treatment & Management." Medscape. Updated Oct 23, 2015.
<http://emedicine.medscape.com/article/1175560-treatment#d1>

Olson, D.A., MD. "Mercury Toxicity Workup." Medscape. Updated: Oct 23,2015.
<http://emedicine.medscape.com/article/1175560-workup#c7>

U.S. Environmental Protection Agency. Mercury in Your Environment. Updated: Jul 26, 2016.
<https://www.epa.gov/mercury>

Last Editorial Review: 9/12/2016

Reviewed on 9/12/2016
References
REFERENCES:

American Academy of Pediatrics. "How to Take a Child's Temperature." Nov 21, 2015.
<https://www.healthychildren.org/English/health-issues/conditions/fever/Pages/How-to-Take-a-Childs-Temperature.aspx>

Environmental Defense Fund. Mercury alert: Is canned tuna safe to eat?
<https://www.edf.org/oceans/mercury-alert-canned-tuna-safe-eat>

Menon, Shanti. "Mercury Guide." Natural Resources Defense Council. Updated: Mar 10, 2016.
<https://www.nrdc.org/stories/mercury-guide>

Olson, D.A., MD. "Mercury Toxicity Treatment & Management." Medscape. Updated Oct 23, 2015.
<http://emedicine.medscape.com/article/1175560-treatment#d1>

Olson, D.A., MD. "Mercury Toxicity Workup." Medscape. Updated: Oct 23,2015.
<http://emedicine.medscape.com/article/1175560-workup#c7>

U.S. Environmental Protection Agency. Mercury in Your Environment. Updated: Jul 26, 2016.
<https://www.epa.gov/mercury>

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