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How People are Exposed to Mercury


Mercury exists in various forms, and people are exposed to each in different ways. The most common way people in the U.S. are exposed to mercury is by eating fish containing methylmercury. Other exposures may result from using or breaking products containing mercury.

If you are concerned for your health or your family's as a result of exposure to mercury, get in touch with your health care provider. They will be able to tell you if mercury exposure is a problem for you and what to do about it.

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Exposure to Methylmercury

Although most people have mercury levels in their bodies below the level associated with possible health effects, almost all people in the world have at least trace amounts of methylmercury in their bodies, reflecting its pervasive presence in the environment. Nearly all methylmercury exposures in the U.S. occur through eating fish and shellfish that contain higher levels of methylmercury.

Populations Particularly Sensitive to Methylmercury Exposures

Some communities eat significantly more quantities of fish than the general population, and thus may be exposed to much greater mercury contamination than the general population.

In addition, in past outbreaks of methylmercury poisoning, mothers with no symptoms of nervous system damage gave birth to infants with severe disabilities; as a result, it became clear that the nervous system of a developing fetus may be more vulnerable to methylmercury exposures than the adult nervous system. Mothers who are exposed to methylmercury and breast-feed may also expose their infant children through their milk.

How Mercury Enters the Environment

Graphic showing mercury emitted from power plants, wet and dry deposition into water, and bioaccumulation in fish, leading to mercury exposure for people and wildlifeMercury is emitted to the air by human activities, such as manufacturing or burning coal for fuel, and from natural sources, such as volcanoes.

Typically, mercury is released into the atmosphere in one of three forms:

What happens to mercury after it is emitted depends on several factors:

Depending on these factors, atmospheric mercury can be transported over a range of distances before it is deposited, potentially resulting in deposition on local, regional, continental and/or global scales. Mercury that remains in the air for prolonged periods of time and travels across continents is said to be in the "global cycle."

Mercury Emissions Around the Globe

Recent emissions estimates of annual global mercury emissions from all sources, natural and anthropogenic (human-generated), which are highly uncertain, are about 5,000-8,000 metric tons per year.

U.S. anthropogenic mercury emissions are estimated to account for roughly three percent of the total global emissions, and the U.S. power sector is estimated to account for about one percent the total global emissions. EPA has estimated that about one-third of U.S. emissions are deposited within the contiguous U.S. and the remainder enters the global cycle.

Current estimates are that less than half of all mercury deposition within the U.S. comes from U.S. sources, although deposition varies by geographic location. For example, compared to the country as a whole, U.S. sources represent a greater fraction of the total deposition in parts of the Northeast because of the direction of the prevailing winds.

Source: Technical Background Report for the Global Mercury Assessment 2013 Exit EPA Disclaimer

Learn more about the mercury emissions around the globe.

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Moving Up the Food Chain

When mercury falls in rain or snow, it may flow into bodies of water like lakes and streams. When it falls out of the air as dry deposition, it may eventually be washed into those bodies by rain. Bacteria in soils and sediments convert mercury to methylmercury. In this form, it is taken up by tiny aquatic plants and animals. Fish that eat these organisms build up methylmercury in their bodies. As ever-bigger fish eat smaller ones, the methylmercury is concentrated further up the food chain. This process is called "bioaccumulation".

Methylmercury concentrations in fish depend on many factors, including mercury, the concentration in water, water pH and temperature, the amount of dissolved solids and organic matter in the water, and what organisms live in the water. Methylmercury concentrations in fish may also be affected by the presence of sulfur and other chemicals in the water. Because of these variables, and because food webs are very complex, bioaccumulation is hard to predict and can vary from one water body to another.

Graphic showing how mercury becomes more concentrated as larger animals eat smaller ones However, in a given water body, the highest concentrations of methylmercury are generally found in large fish that eat other fish. The concentrations of methylmercury in large fish can be over a million-fold larger than in the surrounding water. EPA discussions of estimates bioaccumulation can be found in Chapter 6 and Appendix A of the Water Quality Criterion for the Protection of Human Health: Methylmercury.

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What EPA and Other Federal Agencies are Doing to Help Reduce Exposures to Methylmercury

Reference Dose (RfD):
Formal Definition

An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data used. Generally used in EPA's noncancer health assessments.

No-Observed-Adverse-Effect Level (NOAEL): The highest exposure level at which there are no biologically significant increases in the frequency or severity of adverse effect between the exposed population and its appropriate control; some effects may be produced at this level, but they are not considered adverse or precursors of adverse effects.

Lowest-Observed-Adverse- Effect Level (LOAEL): The lowest exposure level at which there are biologically significant increases in frequency or severity of adverse effects between the exposed population and its appropriate control group

Understanding What Levels of Mercury Exposure Might Affect Human Health

In 1997, EPA published the Mercury Study Report to Congress to fulfill requirements of the Clean Air Act Amendments of 1990. The report is an eight-volume assessment of the magnitude of U.S. mercury emissions by source; the health and environmental impacts of those emissions; and the availability and cost of control technologies.

EPA has also calculated a reference dose (RfD) level for methylmercury. An RfD is EPA’s estimate of the maximum acceptable daily exposure to humans that is not likely to cause harmful effects during a lifetime (see a more detailed definition in the box at right). EPA's RfD for methylmercury, last revised in 2001, is currently 0.1 micrograms per kilogram of body weight per day.

Measuring and Monitoring the Number of People at Risk from Methylmercury Exposure

Human biological monitoring by the Centers for Disease Control and Prevention shows that most people have blood mercury levels below the level associated with possible health effects [CDC, 2009-2010].

As described in EPA's 2013 report Trends in Blood Mercury Concentrations and Fish Consumption Among U.S. Women of Reproductive Age, NHANES, 1999-2010 (PDF) (1.5 MB, 81 pp., about PDF), blood mercury analyses in the 2009-2010 National Health and Nutrition Examination Survey for 16-to-49-year-old women showed that approximately 2.3% of women had blood mercury concentrations greater than 5.8 micrograms per liter (which is a blood mercury level equivalent to the current RfD). This percentage represents an estimated 1.4 million women of reproductive age who have blood mercury concentrations that may increase the risk of learning disabilities in their unborn children. Based on this prevalence and the number of U.S. births each year [Martin et al, 2012], it is estimated that more than 75,000 newborns each year may have increased risk of learning disabilities associated with in-utero exposure to methylmercury.

Sources

Providing Consumers with Advice to Reduce Exposures

In 2004 EPA and FDA issued the first-ever joint consumer advice about methylmercury in fish and shellfish. This advice was for women who might become pregnant; women who are pregnant; nursing mothers; and young children. The advisory provides recommendations for selecting and eating fish and shellfish. By following the recommendations, women and young children will receive the benefits of eating fish and shellfish and be confident that they have reduced their exposure to the harmful effects of methylmercury.

U.S. states also issue advisories to limit or avoid eating fish or shellfish caught from particular bodies of water.

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Exposures to Elemental Mercury

When elemental mercury is spilled or a device containing mercury breaks, the exposed elemental mercury can evaporate and become an invisible, odorless toxic vapor. This is especially true in warm or poorly-ventilated rooms or spaces. Sources of potential exposure to elemental mercury are described below.

What EPA and Other Federal Agencies are Doing to Help Reduce Exposures to Elemental Mercury

Developing Technologies to Prevent Mercury Emissions into the Air

To reduce airborne mercury emissions from small-scale gold buying and refining facilities located in over 55 countries around the world, EPA and the Argonne National Laboratory (ANL) have partnered to design a low cost, easily constructible technology called the Gold Shop Mercury Capture System (MCS). Learn more about the Gold Shop MCS Project.

Participating in Other International Projects

The U.S. engages its international partners, multilaterally and bilaterally, to address key mercury issues such as:

Learn more about EPA's international work on mercury.

Engaging in Partnerships and Consumer Outreach to Promote Voluntary Reductions in Mercury Use and Releases

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Exposures to Other Mercury Compounds (Inorganic and Organic)

Inorganic mercury compounds take the form of mercury salts. They are generally white powders or crystals, with the exception of mercuric sulfide (cinnabar) which is red. Inorganic compounds and organic compounds (such as phenylmercury acetate and ethylmercury), have been commonly used as fungicides, antiseptics or disinfectants. They have also been used in a variety of products. Most of these uses have been discontinued, but small amounts of these compounds can still be found as preservatives in some medicines. The U.S. Food and Drug Administration maintains a list of medicines that contain mercury.

Excessive exposure to inorganic and organic mercury compounds can result from misuse or overuse of mercury-containing products, especially outdated products containing more mercury. Exposure to mercury compounds is primarily through ingestion, but can occur through other pathways. Ingested organic mercury compounds are more readily absorbed through the gastrointestinal tract than are inorganic compounds.

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