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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for Mercury. 

It is one in a series of Public Health Statements 

about hazardous substances and their health effects. 

A shorter version, the ToxFAQsTM, is also 

available. This information is important because 

this substance may harm you. The effects of 

exposure to any hazardous substance depend on the 

dose, the duration, how you are exposed, personal 

traits and habits, and whether other chemicals are 

present. For more information, call the ATSDR 

Information Center at 1-888-422-8737. 

This public health statement tells you about 

mercury and the effects of exposure. 

The Environmental Protection Agency (EPA) 

identifies the most serious hazardous waste sites in 

the nation. These sites make up the National 

Priorities List (NPL) and are the sites targeted for 

long-term federal cleanup activities. Mercury has 

been found in at least 714 of the 1,467 current or 

former NPL sites. However, the total number of 

NPL sites evaluated for this substance is not known. 

As more sites are evaluated, the sites at which 

mercury is found may increase. This information is 

important because exposure to this substance may 

harm you and because these sites may be sources of 

exposure. 

When a substance is released from a large area, 

such as an industrial plant, or from a container, such 

as a drum or bottle, it enters the environment. This 

release does not always lead to exposure. You are 

exposed to a substance only when you come in 

contact with it. You may be exposed by breathing, 

eating, or drinking the substance or by skin contact. 

If you are exposed to mercury, many factors 

determine whether you'll be harmed. These factors 

include the dose (how much), the duration (how 

long), and how you come in contact with it. You 

must also consider the other chemicals to which 

you're exposed, as well as your age, sex, diet, 

family traits, lifestyle, and state of health. 

1.1 WHAT IS MERCURY? 

Mercury occurs naturally in the environment and 

exists in several forms. These forms can be 

organized under three headings: metallic mercury 

(also known as elemental mercury), inorganic 

mercury, and organic mercury. Metallic mercury is 

a shiny, silver-white metal that is a liquid at room 

temperature. Metallic mercury is the elemental or 

pure form of mercury (i.e., it is not combined with 

other elements). Metallic mercury metal is the 

familiar liquid metal used in thermometers and 

some electrical switches. At room temperature, 

some of the metallic mercury will evaporate and 

form mercury vapors. Mercury vapors are colorless 

and odorless. The higher the temperature, the more 

vapors will be released from liquid metallic 

mercury. Some people who have breathed mercury 

vapors report a metallic taste in their mouths. 

Metallic mercury has been found at 714 hazardous 

waste sites nationwide. 

Inorganic mercury compounds occur when mercury 

combines with elements such as chlorine, sulfur, or 

oxygen. These mercury compounds are also called 

mercury salts. Most inorganic mercury compounds 

are white powders or crystals, except for mercuric 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

sulfide (also known as cinnabar) which is red and 

turns black after exposure to light. 

When mercury combines with carbon, the 

compounds formed are called "organic" mercury 

compounds or organomercurials. There is a 

potentially large number of organic mercury 

compounds; however, by far the most common 

organic mercury compound in the environment is 

methylmercury (also known as 

monomethylmercury). In the past, an organic 

mercury compound called phenylmercury was used 

in some commercial products. Another organic 

mercury compound called dimethylmercury is also 

used in small amounts as a reference standard for 

some chemical tests. Dimethylmercury is the only 

organic mercury compound that has been identified 

at hazardous waste sites. It was only found in 

extremely small amounts at two hazardous waste 

sites nationwide, but it is very harmful to people 

and animals. Like the inorganic mercury 

compounds, both methylmercury and 

phenylmercury exist as "salts" (for example, 

methylmercuric chloride or phenylmercuric 

acetate). When pure, most forms of methylmercury 

and phenylmercury are white crystalline solids. 

Dimethylmercury, however, is a colorless liquid. 

Several forms of mercury occur naturally in the 

environment. The most common natural forms of 

mercury found in the environment are metallic 

mercury, mercuric sulfide (cinnabar ore), mercuric 

chloride, and methylmercury. Some 

microorganisms (bacteria and fungi) and natural 

processes can change the mercury in the 

environment from one form to another. The most 

common organic mercury compound that 

microorganisms and natural processes generate 

from other forms is methylmercury. 

Methylmercury is of particular concern because it 

can build up in certain edible freshwater and 

saltwater fish and marine mammals to levels that 

are many times greater than levels in the 

surrounding water. 

Mercury is mined as cinnabar ore, which contains 

mercuric sulfide. The metallic form is refined from 

mercuric sulfide ore by heating the ore to 

temperatures above 1,000 degrees Fahrenheit. This 

vaporizes the mercury in the ore, and the vapors are 

then captured and cooled to form the liquid metal 

mercury. There are many different uses for liquid 

metallic mercury. It is used in producing of 

chlorine gas and caustic soda, and in extracting gold 

from ore or articles that contain gold. It is also used 

in thermometers, barometers, batteries, and 

electrical switches. Silver-colored dental fillings 

typically contain about 50% metallic mercury. 

Metallic mercury is still used in some herbal or 

religious remedies in Latin America and Asia, and 

in rituals or spiritual practices in some Latin 

American and Caribbean religions such as Voodoo, 

Santeria, and Espiritismo. These uses may pose a 

health risk from exposure to mercury both for the 

user and for others who may be exposed to mercury 

vapors in contaminated air. 

Some inorganic mercury compounds are used as 

fungicides. Inorganic salts of mercury, including 

ammoniated mercuric chloride and mercuric iodide, 

have been used in skin-lightening creams. Mercuric 

chloride is a topical antiseptic or disinfectant agent. 

In the past, mercurous chloride was widely used in 

medicinal products including laxatives, worming 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

medications, and teething powders. It has since 

been replaced by safer and more effective agents. 

Other chemicals containing mercury are still used as 

antibacterials. These products include 

mercurochrome (contains a small amount of 

mercury, 2%), and thimerosal and phenylmercuric 

nitrate, which are used in small amounts as 

preservatives in some prescription and over-thecounter medicines. Mercuric sulfide and mercuric 

oxide may be used to color paints, and mercuric 

sulfide is one of the red coloring agents used in 

tattoo dyes. 

Methylmercury is produced primarily by 

microorganisms (bacteria and fungi) in the 

environment, rather than by human activity. Until 

the 1970s, methylmercury and ethylmercury 

compounds were used to protect seed grains from 

fungal infections. Once the adverse health effects 

of methylmercury were known, the use of 

methymercury and ethylmercury as fungicides was 

banned. Up until 1991, phenylmercuric compounds 

were used as antifungal agents in both interior and 

exterior paints, but this use was also banned 

because mercury vapors were released from these 

paints. 

1.2 WHAT HAPPENS TO MERCURY WHEN 

IT ENTERS THE ENVIRONMENT? 

Mercury is a naturally occurring metal found 

throughout the environment. Mercury enters the 

environment as the result of the normal breakdown 

of minerals in rocks and soil from exposure to wind 

and water, and from volcanic activity. Mercury 

releases from natural sources have remained 

relatively constant in recent history, resulting in a 

steady rise in environmental mercury. Human 

activities since the start of the industrial age (e.g., 

mining, burning of fossil fuels) have resulted in 

additional release of mercury to the environment. 

Estimates of the total annual mercury releases that 

result from human activities range from one-third to 

two-thirds of the total mercury releases. A major 

uncertainty in these estimates is the amount of 

mercury that is released from water and soils that 

were previously contaminated by human activities 

as opposed to new natural releases. The levels of 

mercury in the atmosphere (i.e., the air you breathe 

in the general environment) are very, very low and 

do not pose a health risk; however, the steady 

release of mercury has resulted in current levels that 

are three to six times higher than the estimated 

levels in the preindustrial era atmosphere. 

Approximately 80% of the mercury released from 

human activities is elemental mercury released to 

the air, primarily from fossil fuel combustion, 

mining, and smelting, and from solid waste 

incineration. About 15% of the total is released to 

the soil from fertilizers, fungicides, and municipal 

solid waste (for example, from waste that contains 

discarded batteries, electrical switches, or 

thermometers). An additional 5% is released from 

industrial wastewater to water in the environment. 

With the exception of mercury ore deposits, the 

amount of mercury that naturally exists in any one 

place is usually very low. In contrast, the amount of 

mercury that may be found in soil at a particular 

hazardous waste site because of human activity can 

be high (over 200,000 times natural levels). The 

mercury in air, water, and soil at hazardous waste 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

sites may come from both natural sources and 

human activity. 

Most of the mercury found in the environment is in 

the form of metallic mercury and inorganic mercury 

compounds. Metallic and inorganic mercury enters 

the air from mining deposits of ores that contain 

mercury, from the emissions of coal-fired power 

plants, from burning municipal and medical waste, 

from the production of cement, and from 

uncontrolled releases in factories that use mercury. 

Metallic mercury is a liquid at room temperature, 

but some of the metal will evaporate into the air and 

can be carried long distances. In air, the mercury 

vapor can be changed into other forms of mercury, 

and can be further transported to water or soil in 

rain or snow. Inorganic mercury may also enter 

water or soil from the weathering of rocks that 

contain mercury, from factories or water treatment 

facilities that release water contaminated with 

mercury, and from incineration of municipal 

garbage that contains mercury (for example, in 

thermometers, electrical switches, fluorescent light 

bulbs, or batteries that have been thrown away). 

Inorganic or organic compounds of mercury may be 

released to the water or soil if mercury-containing 

fungicides are used. 

Microorganisms (bacteria, phytoplankton in the 

ocean, and fungi) convert inorganic mercury to 

methylmercury. Methylmercury released from 

microorganisms can enter the water or soil and 

remain there for a long time, particularly if the 

methylmercury becomes attached to small particles 

in the soil or water. Mercury usually stays on the 

surface of sediments or soil and does not move 

through the soil to underground water. If mercury 

enters the water in any form, it is likely to settle to 

the bottom where it can remain for a long time. 

Mercury can enter and accumulate in the food 

chain. The form of mercury that accumulates in the 

food chain is methylmercury. Inorganic mercury 

does not accumulate up the food chain to any 

extent. When small fish eat the methylmercury in 

food, it goes into their tissues. When larger fish eat 

smaller fish or other organisms that contain 

methylmercury, most of the methylmercury 

originally present in the small fish will then be 

stored in the bodies of the larger fish. As a result, 

the larger and older fish living in contaminated 

waters build up the highest amounts of 

methylmercury in their bodies. Saltwater fish 

(especially sharks and swordfish) that live a long 

time and can grow to a very large size tend to have 

the highest levels of mercury in their bodies. Plants 

(such as corn, wheat, and peas) have very low levels 

of mercury, even if grown in soils containing 

mercury at significantly higher than background 

levels. Mushrooms, however, can accumulate high 

levels if grown in contaminated soils. 

1.3 HOW MIGHT I BE EXPOSED TO 

MERCURY? 

Because mercury occurs naturally in the 

environment, everyone is exposed to very low 

levels of mercury in air, water, and food. Between 

10 and 20 nanograms of mercury per cubic meter 

(ng/m3) of air have been measured in urban outdoor 

air. These levels are hundreds of times lower than 

levels still considered to be "safe" to breathe. 

Background levels in nonurban settings are even 

lower, generally about 6 ng/m3or less. Mercury 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

levels in surface water are generally less than 5 

parts of mercury per trillion parts of water (5 ppt, or 

5 ng per liter of water), about a thousand times 

lower than "safe" drinking water standards. Normal 

soil levels range from 20 to 625 parts of mercury 

per billion parts of soil (20–625 ppb; or 20,000– 

625,000 ng per kilogram of soil). A part per billion 

is one thousand times bigger than a part per trillion. 

A potential source of exposure to metallic mercury 

for the general population is mercury released from 

dental amalgam fillings. An amalgam is a mixture 

of metals. The amalgam used in silver-colored 

dental fillings contains approximately 50% metallic 

mercury, 35% silver, 9% tin, 6% copper, and trace 

amounts of zinc. When the amalgam is first mixed, 

it is a soft paste which is inserted into the tooth 

surface. It hardens within 30 minutes. Once the 

amalgam is hard, the mercury is bound within the 

amalgam, but very small amounts are slowly 

released from the surface of the filling due to 

corrosion or chewing or grinding motions. Part of 

the mercury at the surface of the filling may enter 

the air as mercury vapor or be dissolved in the 

saliva. The total amount of mercury released from 

dental amalgam depends upon the total number of 

fillings and surface areas of each filling, the 

chewing and eating habits of the person, and other 

chemical conditions in the mouth. Estimates of the 

amount of mercury released from dental amalgams 

range from 3 to 17 micrograms per day (μg/day). 

The mercury from dental amalgam may contribute 

from 0 to more than 75% of your total daily 

mercury exposure, depending on the number of 

amalgam fillings you have, the amount of fish 

consumed, the levels of mercury (mostly as 

methylmercury) in those fish, and exposure from 

other less common sources such as mercury spills, 

religious practices, or herbal remedies that contain 

mercury. However, it should be kept in mind that 

exposure to very small amounts of mercury, such as 

that from dental amalgam fillings, does not 

necessarily pose a health risk. 

Whether the levels of exposure to mercury vapor 

from dental amalgam are sufficiently high to cause 

adverse health effects, and exactly what those 

effects are, continues to be researched and debated 

by scientists and health officials. U.S. government 

summaries on the effects of dental amalgam 

conclude that there is no apparent health hazard to 

the general population, but that further study is 

needed to determine the possibility of more subtle 

behavioral or immune system effects, and to 

determine the levels of exposure that may lead to 

adverse effects in sensitive populations. Sensitive 

populations may include pregnant women, children 

under the age of 6 (especially up to the age of 3), 

people with impaired kidney function, and people 

with hypersensitive immune responses to metals. If 

you belong to this group, you should discuss your 

medical condition with your dentist prior to any 

dental restoration work. Removal of dental 

amalgams in people who have no indication of 

adverse effects is not recommended and can put the 

person at greater risk, if performed improperly. 

Chelation therapy (used to remove metals from the 

body tissues) itself presents some health risks, and 

should be considered only when a licensed 

occupational or environmental health physician 

determines it necessary to reduce immediate and 

significant health risks due to high levels of 

mercury in the body. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

Some religions have practices that may include the 

use of metallic mercury. Examples of these 

religions include Santeria (a Cuban-based religion 

whose followers worship both African deities and 

Catholic saints), Voodoo (a Haitian-based set of 

beliefs and rituals), Palo Mayombe (a secret form of 

ancestor worship practiced mainly in the 

Caribbean), and Espiritismo (a spiritual belief 

system native to Puerto Rico). Not all people who 

observe these religions use mercury, but when 

mercury is used in religious, ethnic, or ritualistic 

practices, exposure to mercury may occur both at 

the time of the practice and afterwards from 

contaminated indoor air. Metallic mercury is sold 

under the name "azogue" (pronounced ah-SEWgay) in stores called "botanicas." Botanicas are 

common in Hispanic and Haitian communities, 

where azogue may be sold as an herbal remedy or 

for spiritual practices. The metallic mercury is 

often sold in capsules or in glass containers. It may 

be placed in a sealed pouch to be worn on a 

necklace or in a pocket, or it may be sprinkled in the 

home or car. Some people may mix azogue in bath 

water or perfume, or place azogue in devotional 

candles. Because metallic mercury evaporates into 

the air, these practices may put anyone breathing 

the air in the room at risk of exposure to mercury. 

The longer people breathe the contaminated air, the 

greater their risk will be. The use of metallic 

mercury in a home or an apartment not only 

threatens the health of the people who live there 

now, but also threatens the health of future residents 

who may unknowingly be exposed to further release 

of mercury vapors from contaminated floors or 

walls. 

Metallic mercury is used in a variety of household 

products and industrial items, including thermostats, 

fluorescent light bulbs, barometers, glass 

thermometers, and some blood pressure devices. 

The mercury in these devices is contained in glass 

or metal, and generally does not pose a risk unless 

the item is damaged or broken, and mercury vapors 

are released. Spills of metallic mercury from 

broken thermometers or damaged electrical 

switches in the home may result in exposure to 

mercury vapors in indoor air. You must be careful 

when you handle and dispose of all items in the 

home that contain metallic mercury. 

Very small amounts of metallic mercury (for 

example, a few drops) can raise air concentrations 

of mercury to levels that may be harmful to health. 

The longer people breathe the contaminated air, the 

greater the risk to their health. Metallic mercury 

and its vapors are extremely difficult to remove 

from clothes, furniture, carpet, floors, walls, and 

other such items. If these items are not properly 

cleaned, the mercury can remain for months or 

years, and continue to be a source of exposure. 

It is possible for you to be exposed to metallic 

mercury vapors from breathing contaminated air 

around hazardous waste sites, waste incinerators, or 

power plants that burn mercury-containing fuels 

(such as coal or other fossil fuels), but most outdoor 

air is not likely to contain levels that would be 

harmful. Exposure to mercury compounds at 

hazardous waste sites is much more likely to occur 

from handling contaminated soil (i.e., children 

playing in or eating contaminated surface soil), 

drinking well-water, or eating fish from 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

contaminated waters near those sites. Not all 

hazardous sites contain mercury, and not all waste 

sites that do contain mercury have releases of 

mercury to the air, water, or surface soils. 

You can be exposed to mercury vapors from the use 

of fungicides that contain mercury. Excess use of 

these products may result in higher-than-average 

exposures. You may also be exposed to mercury 

from swallowing or applying to your skin outdated 

medicinal products (laxatives, worming 

medications, and teething powders) that contain 

mercurous chloride. Exposure may also occur from 

the improper or excessive use of other chemicals 

containing mercury, such as skin-lightening creams 

and some topical antiseptic or disinfectant agents 

(mercurochrome and thimerosal). 

Workers are mostly exposed from breathing air that 

contains mercury vapors, but may also be exposed 

to other inorganic mercury compounds in the 

workplace. Occupations that have a greater 

potential for mercury exposure include 

manufacturers of electrical equipment or 

automotive parts that contain mercury, chemical 

processing plants that use mercury, metal 

processing, construction where building parts 

contain mercury (e.g., electrical switches, 

thermometers), and the medical professions 

(medical, dental, or other health services) where 

equipment may contain mercury (e.g., some devices 

that measure blood pressure contain liquid 

mercury). Dentists and their assistants may be 

exposed to metallic mercury from breathing in 

mercury vapor released from amalgam fillings and 

to a much lesser extent from skin contact with 

amalgam restorations. Family members of workers 

who have been exposed to mercury may also be 

exposed to mercury if the worker's clothes are 

contaminated with mercury particles or liquid. 

Some people may be exposed to higher levels of 

mercury in the form of methylmercury if they have 

a diet high in fish, shellfish, or marine mammals 

(whales, seals, dolphins, and walruses) that come 

from mercury-contaminated waters. 

Methylmercury accumulates up the food chain, so 

that fish at the top of the food chain will have the 

most mercury in their flesh. Of these fish, the 

largest (i.e., the oldest) fish will have the highest 

levels. The Food and Drug Administration (FDA) 

estimates that most people are exposed, on average, 

to about 50 ng of mercury per kilogram of body 

weight per day (50 ng/kg/day) in the food they eat. 

This is about 3.5 micrograms (μg) of mercury per 

day for an adult of average weight. This level is not 

thought to result in any harmful effects. A large 

part of this mercury is in the form of methylmercury 

and probably comes from eating fish. Commercial 

fish sold through interstate commerce that are found 

to have levels of methylmercury above an "action 

level" of 1 ppm (established by the FDA) cannot be 

sold to the public. This level itself is below a level 

associated with adverse effects. However, if you 

fish in contaminated waters and eat the fish you 

catch, you may be exposed to higher levels of 

mercury. Public health advisories are issued by 

state and federal authorities for local waters that are 

thought to be contaminated with mercury. These 

advisories can help noncommercial (sport and 

subsistence) fishermen and their families to avoid 

eating fish contaminated with mercury. Foods other 

than fish that may contain higher than average 

levels of mercury include wild game, such as wild 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

birds and mammals (bear) that eat large amounts of 

contaminated fish. People in the most northern 

climates may be exposed to high levels of mercury 

from eating meat or fat from marine mammals 

including whales, dolphins, walruses, and seals. 

These marine mammals are at or near the top of 

their marine food chain. Plants contain very little 

methylmercury or other forms of mercury. 

Mushrooms grown in mercury-contaminated soil 

may contain levels of mercury that could pose some 

risk to health, if large amounts were eaten. 

1.4 HOW CAN MERCURY ENTER AND 

LEAVE MY BODY? 

A person can be exposed to mercury from breathing 

in contaminated air, from swallowing or eating 

contaminated water or food, or from having skin 

contact with mercury. Not all forms of mercury 

easily enter your body, even if they come in contact 

with it; so it is important to know which form of 

mercury you have been exposed to, and by which 

route (air, food, or skin). 

When you swallow small amounts of metallic 

mercury, for example, from a broken oral 

thermometer, virtually none (less than 0.01%) of the 

mercury will enter your body through the stomach 

or intestines, unless they are diseased. Even when a 

larger amount of metal mercury (a half of a 

tablespoon, about 204 grams) was swallowed by 

one person, very little entered the body. When you 

breathe in mercury vapors, however, most (about 

80%) of the mercury enters your bloodstream 

directly from your lungs, and then rapidly goes to 

other parts of your body, including the brain and 

kidneys. Once in your body, metallic mercury can 

stay for weeks or months. When metallic mercury 

enters the brain, it is readily converted to an 

inorganic form and is "trapped" in the brain for a 

long time. Metallic mercury in the blood of a 

pregnant woman can enter her developing child. 

Most of the metallic mercury will accumulate in 

your kidneys, but some metallic mercury can also 

accumulate in the brain. Most of the metallic 

mercury absorbed into the body eventually leaves in 

the urine and feces, while smaller amounts leave the 

body in the exhaled breath. 

Inorganic mercury compounds like mercurous 

chloride and mercuric chloride are white powders 

and do not generally vaporize at room temperatures 

like elemental mercury will. If they are inhaled, 

they are not expected to enter your body as easily as 

inhaled metallic mercury vapor. When inorganic 

mercury compounds are swallowed, generally less 

than 10% is absorbed through the intestinal tract; 

however, up to 40% may enter the body through the 

stomach and intestines in some instances. Some 

inorganic mercury can enter your body through the 

skin, but only a small amount will pass through 

your skin compared to the amount that gets into 

your body from swallowing inorganic mercury. 

Once inorganic mercury enters the body and gets 

into the bloodstream, it moves to many different 

tissues. Inorganic mercury leaves your body in the 

urine or feces over a period of several weeks or 

months. A small amount of the inorganic mercury 

can be changed in your body to metallic mercury 

and leave in the breath as a mercury vapor. 

Inorganic mercury accumulates mostly in the 

kidneys and does not enter the brain as easily as 

metallic mercury. Inorganic mercury compounds 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

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Division of Toxicology March 1999 

also do not move as easily from the blood of a 

pregnant woman to her developing child. In a 

nursing woman, some of the inorganic mercury in 

her body will pass into her breast milk. 

Methylmercury is the form of mercury most easily 

absorbed through the gastrointestinal tract (about 

95% absorbed). After you eat fish or other foods 

that are contaminated with methylmercury, the 

methylmercury enters your bloodstream easily and 

goes rapidly to other parts of your body. Only 

small amounts of methylmercury enter the 

bloodstream directly through the skin, but other 

forms of organic mercury (in particular 

dimethylmercury) can rapidly enter the body 

through the skin. Organic mercury compounds may 

evaporate slowly at room temperature and may 

enter your body easily if you breathe in the vapors. 

Once organic mercury is in the bloodstream, it 

moves easily to most tissues and readily enters the 

brain. Methylmercury that is in the blood of a 

pregnant woman will easily move into the blood of 

the developing child and then into the child's brain 

and other tissues. Like metallic mercury, 

methylmercury can be changed by your body to 

inorganic mercury. When this happens in the brain, 

the mercury can remain there for a long time. 

When methylmercury does leave your body after 

you have been exposed, it leaves slowly over a 

period of several months, mostly as inorganic 

mercury in the feces. As with inorganic mercury, 

some of the methylmercury in a nursing woman's 

body will pass into her breast milk. 

1.5 HOW CAN MERCURY AFFECT MY 

HEALTH? 

The nervous system is very sensitive to mercury. In 

poisoning incidents that occurred in other countries, 

some people who ate fish contaminated with large 

amounts of methylmercury or seed grains treated 

with methylmercury or other organic mercury 

compounds developed permanent damage to the 

brain and kidneys. Permanent damage to the brain 

has also been shown to occur from exposure to 

sufficiently high levels of metallic mercury. 

Whether exposure to inorganic mercury results in 

brain or nerve damage is not as certain, since it does 

not easily pass from the blood into the brain. 

Metallic mercury vapors or organic mercury may 

affect many different areas of the brain and their 

associated functions, resulting in a variety of 

symptoms. These include personality changes 

(irritability, shyness, nervousness), tremors, changes 

in vision (constriction (or narrowing) of the visual 

field), deafness, muscle incoordination, loss of 

sensation, and difficulties with memory. 

Different forms of mercury have different effects on 

the nervous system, because they do not all move 

through the body in the same way. When metallic 

mercury vapors are inhaled, they readily enter the 

bloodstream and are carried throughout the body 

and can move into the brain. Breathing in or 

swallowing large amounts of methylmercury also 

results in some of the mercury moving into the 

brain and affecting the nervous system. Inorganic 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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mercury salts, such as mercuric chloride, do not 

enter the brain as readily as methylmercury or 

metallic mercury vapor. 

The kidneys are also sensitive to the effects of 

mercury, because mercury accumulates in the 

kidneys and causes higher exposures to these 

tissues, and thus more damage. All forms of 

mercury can cause kidney damage if large enough 

amounts enter the body. If the damage caused by 

the mercury is not too great, the kidneys are likely 

to recover once the body clears itself of the 

contamination. 

Short-term exposure (hours) to high levels of 

metallic mercury vapor in the air can damage the 

lining of the mouth and irritate the lungs and 

airways, causing tightness of the chest, a burning 

sensation in the lungs, and coughing. Other effects 

from exposure to mercury vapor include nausea, 

vomiting, diarrhea, increases in blood pressure or 

heart rate, skin rashes, and eye irritation. Damage 

to the lining of the mouth and lungs can also occur 

from exposure to lower levels of mercury vapor 

over longer periods (for example, in some 

occupations where workers were exposed to 

mercury for many years). Levels of metallic 

mercury in workplace air are generally much 

greater than the levels normally encountered by the 

general population. Current levels of mercury in 

workplace air are low, due to increased awareness 

of mercury's toxic effects. Because of the reduction 

in the allowable amount of mercury in workplace 

air, fewer workers are expected to have symptoms 

of mercury toxicity. Most studies of humans who 

breathed metallic mercury for a long time indicate 

that mercury from this type of exposure does not 

affect the ability to have children. Studies in 

workers exposed to metallic mercury vapors have 

also not shown any mercury-related increase in 

cancer. Skin contact with metallic mercury has 

been shown to cause an allergic reaction (skin 

rashes) in some people. 

In addition to effects on the kidneys, inorganic 

mercury can damage the stomach and intestines, 

producing symptoms of nausea, diarrhea, or severe 

ulcers if swallowed in large amounts. Effects on the 

heart have also been observed in children after they 

accidentally swallowed mercuric chloride. 

Symptoms included rapid heart rate and increased 

blood pressure. There is little information on the 

effects in humans from long-term, low-level 

exposure to inorganic mercury. 

To protect the public from the harmful effects of 

toxic chemicals and to find ways to treat people 

who have been harmed, scientists use many tests. 

One way to see if a chemical will hurt people is to 

learn how the chemical is absorbed, used, and 

released by the body; for some chemicals, animal 

testing may be necessary. Animal testing may also 

be used to identify health effects such as cancer or 

birth defects. Without laboratory animals, scientists 

would lose a basic method to get information 

needed to make wise decisions to protect public 

health. Scientists have the responsibility to treat 

research animals with care and compassion. Laws 

today protect the welfare of research animals, and 

scientists must comply with strict animal care 

guidelines. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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Studies using animals indicate that long-term oral 

exposure to inorganic mercury salts causes kidney 

damage, effects on blood pressure and heart rate, 

and effects on the stomach. Study results also 

suggest that reactions involving the immune system 

may occur in sensitive populations after swallowing 

inorganic mercury salts. Some animal studies 

report that nervous system damage occurs after 

long-term exposure to high levels of inorganic 

mercury. Short-term, high-level exposure of 

laboratory animals to inorganic mercury has been 

shown to affect the developing fetus and may cause 

termination of the pregnancy. 

Animals exposed orally to long-term, high levels of 

methylmercury or phenylmercury in laboratory 

studies experienced damage to the kidneys, 

stomach, and large intestine; changes in blood 

pressure and heart rate; adverse effects on the 

developing fetus, sperm, and male reproductive 

organs; and increases in the number of spontaneous 

abortions and stillbirths. Adverse effects on the 

nervous system of animals occur at lower doses 

than do harmful effects to most other systems of the 

body. This difference indicates that the nervous 

system is more sensitive to methylmercury toxicity 

than are other organs in the body. Animal studies 

also provide evidence of damage to the nervous 

system from exposure to methylmercury during 

development, and evidence suggests that the effects 

worsen with age, even after the exposure stops. 

Some rat and mice strains that are susceptible to 

autoimmune responses develop kidney damage as a 

result of an immune response when exposed to 

relatively low levels of mercury vapor or mercury 

chloride. 

Animals given inorganic mercury salts by mouth for 

most of their lifetime had increases in some kinds of 

tumors at the highest dose tested. Rats and mice 

that received organic mercury (methylmercury or 

phenylmercury) in their drinking water or feed for 

most of their lives had an increased incidence of 

cancer of the kidney, but this affected only the 

males that received the highest amount of mercury 

given (not the females). Since the high doses 

caused severe damage to the kidneys prior to the 

cancer, these animal studies provide only limited 

information about whether mercury causes cancer in 

humans. As a result, the Department of Health and 

Human Services (DHHS) and the International 

Agency for Research on Cancer (IARC) have not 

classified mercury as to its human carcinogenicity. 

The Environmental Protection Agency has 

determined that mercury chloride and 

methylmercury are possible human carcinogens. 

1.6 HOW CAN MERCURY AFFECT 

CHILDREN? 

This section discusses potential health effects from 

exposures during the period from conception to 

maturity at 18 years of age in humans. Potential 

effects on children resulting from exposures of the 

parents are also considered. 

Children are at risk of being exposed to metallic 

mercury that is not safely contained, to mercury that 

may be brought home on work clothes or tools, or 

to methylmercury-contaminated foods. 

Methylmercury eaten or swallowed by a pregnant 

woman or metallic mercury that enters her body 

from breathing contaminated air can also pass into 

the developing child. Inorganic mercury and 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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methylmercury can also pass from a mother's body 

into breast milk and into a nursing infant. The 

amount of mercury in the milk will vary, depending 

on the degree of exposure and the amount of 

mercury that enter the nursing woman's body. 

There are significant benefits to breast feeding, so 

any concern that a nursing woman may have about 

mercury levels in her breast milk should be 

discussed with her doctor. Methylmercury can also 

accumulate in an unborn baby's blood to a 

concentration higher than the concentration in the 

mother. 

For similar exposure routes and forms of mercury, 

the harmful health effects seen in children are 

similar to the effects seen in adults. High exposure 

to mercury vapor causes lung, stomach, and 

intestinal damage and death due to respiratory 

failure in severe cases. These effects are similar to 

those seen in adult groups exposed to inhaled 

metallic mercury vapors at work. 

Children who had been exposed to excessive 

amounts of mercurous chloride tablets for worms or 

mercurous chloride-containing powders for teething 

discomfort had increased heart rates and elevated 

blood pressure. Abnormal heart rhythms were also 

seen in children who had eaten grains contaminated 

with very high levels of methylmercury. 

Other symptoms of poisonings in children who 

were treated with mercurous chloride for 

constipation, worms, or teething discomfort 

included swollen red gums, excessive salivation, 

weight loss, diarrhea and/or abdominal pain, and 

muscle twitching or cramping in the legs and/or 

arms. Kidney damage is very common after 

exposure to toxic levels of inorganic mercury. 

Metallic mercury or methylmercury that enters the 

body can also be converted to inorganic mercury 

and result in kidney damage. 

Children who breathe metallic/elemental mercury 

vapors, eat foods or other substances containing 

phenylmercury or inorganic mercury salts, or use 

mercury-containing skin ointments for an extended 

period may develop a disorder known as acrodynia, 

or pink disease. Acrodynia can result in severe leg 

cramps; irritability; and abnormal redness of the 

skin, followed by peeling of the hands, nose, and 

soles of the feet. Itching, swelling, fever, fast heart 

rate, elevated blood pressure, excessive salivation or 

sweating, rashes, fretfulness, sleeplessness, and/or 

weakness may also be present. It was once believed 

that this syndrome occurred only in children, but 

recent reported cases in teenagers and adults have 

shown that they can also develop acrodynia. 

In critical periods of development before they are 

born, and in the early months after birth, children 

and fetuses are particularly sensitive to the harmful 

effects of metallic mercury and methylmercury on 

the nervous system. Harmful developmental effects 

may occur when a pregnant woman is exposed to 

metallic mercury and some of the mercury is 

transferred into her developing child. Thus, women 

who are normally exposed to mercury vapors in the 

workplace (such as those working in 

thermometer/barometer or fluorescent light 

manufacturing or the chlor-alkali industry) should 

take measures to avoid mercury vapor exposures 

during pregnancy. Exposures to mercury vapors 

are relatively rare outside of the workplace, unless 

metallic mercury is present in the home. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

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As with mercury vapors, exposure to 

methylmercury is more dangerous for young 

children than for adults, because more 

methylmercury easily passes into the developing 

brain of young children and may interfere with the 

development process. 

Methylmercury is the form of mercury most 

commonly associated with a risk for developmental 

effects. Exposure can come from foods 

contaminated with mercury on the surface (for 

example, from seed grain treated with 

methylmercury to kill fungus) or from foods that 

contain toxic levels of methylmercury (as in some 

fish, wild game, and marine mammals). Mothers 

who are exposed to methylmercury and breast-feed 

their infant may also expose the child through the 

milk. The effects on the infant may be subtle or 

more pronounced, depending on the amount to 

which the fetus or young child was exposed. In 

cases in which the exposure was relatively small, 

some effects might not be apparent, such as small 

decreases in IQ or effects on the brain that may only 

be determined by the use of very sensitive 

neuropsychological testing. In instances in which 

the exposure is great, the effects may be more 

serious. In some such cases of mercury exposure 

involving serious exposure to the developing fetus, 

the effects are delayed. In such cases, the infant 

may be born apparently normal, but later show 

effects that may range from the infant being slower 

to reach developmental milestones, such as the age 

of first walking and talking, to more severe effects 

including brain damage with mental retardation, 

incoordination, and inability to move. Other severe 

effects observed in children whose mothers were 

exposed to very toxic levels of mercury during 

pregnancy include eventual blindness, involuntary 

muscle contractions and seizures, muscle weakness, 

and inability to speak. It is important to remember, 

however, that the severity of these effects depends 

upon the level of mercury exposure and the length 

of exposure. The very severe effects just mentioned 

were reported in large-scale poisoning instances in 

which pregnant and nursing women were exposed 

to extremely high levels of methylmercury in 

contaminated grain used to make bread (in Iraq) or 

seafood (in Japan) sold to the general population. 

Researchers are currently studying the potential for 

less serious developmental effects, including effects 

on a child's behavior and ability to learn, think, and 

solve problems that may result from eating lower 

levels of methylmercury in foods. A main source of 

exposure to methylmercury for the pregnant woman 

and the young child is from eating fish. Most fish 

purchased in the market in the United States do not 

have mercury levels that pose a risk to anyone, 

including pregnant women. Since mercury 

accumulates in the muscles of fish, larger fish that 

feed on smaller fish and live for long periods 

usually have larger concentrations of 

methylmercury than fish that feed on plants. For 

example, shark and swordfish normally contain the 

highest levels of mercury out of all ocean fish. 

Scientists have an ongoing debate about the value of 

fish in the diet versus any risk from increased 

exposure of pregnant women to methylmercury that 

may be in the fish. The safety of most fish sold 

commercially in the United States is regulated by 

the FDA. These fish pose no health risk to those 

who purchase and eat them. Only fish or wildlife 

containing relatively high levels of methylmercury 

are of concern. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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1.7 HOW CAN FAMILIES REDUCE THE 

RISK OF EXPOSURE TO MERCURY? 

If your doctor finds that you have been exposed to 

significant amounts of mercury, ask whether your 

children might also be exposed. Your doctor might 

need to ask your state health department to 

investigate. 

Children may be exposed to metallic mercury if 

they play with it. Metallic mercury is a heavy, 

shiny, silver liquid. When metallic mercury is 

spilled, it forms little balls or beads. Children are 

sometimes exposed to metallic mercury when they 

find it in abandoned warehouses or closed factories, 

and then play with it or pass it around to friends. 

Children have also taken metallic mercury from 

school chemistry and physics labs. Broken 

thermometers and some electrical switches are other 

sources of metallic mercury. Sometimes children 

find containers of metallic mercury that were 

improperly disposed of, or adults may bring home 

metallic mercury from work, not knowing that it is 

dangerous. 

To protect your children from metallic mercury, 

teach them not to play with shiny, silver liquids. 

Schoolteachers (particularly science teachers) and 

school staff need to know about students' 

fascination with metallic mercury. Teachers and 

school staff should teach children about the dangers 

of getting sick from playing with mercury, and they 

should keep metallic mercury in a safe and secured 

area (such as a closed container in a locked storage 

room) so that children do not have access to it 

without the supervision of a teacher. Metallic 

mercury evaporates slowly, and if it is not stored in 

a closed container, children may breathe toxic 

mercury vapors. 

In the past, mercurous chloride was widely used in 

medicinal products such as laxatives, worming 

medications, and teething powders. These older 

medicines should be properly disposed of and 

replaced with safer and more effective medicines. 

Other chemicals containing mercury, such as 

mercurochrome and thimerosal (sold as Merthiolate 

and other brands), are still used as antiseptics or as 

preservatives in eye drops, eye ointments, nasal 

sprays, and vaccines. Some skin-lightening creams 

contain ammoniated mercuric chloride and mercuric 

iodide. These and all other mercury-containing 

medicines should be kept safely out of the reach of 

children to prevent an accidental poisoning. 

Nonmedicinal products, including some fungicides 

that contain mercury compounds and paints that 

contain mercuric sulfide or mercuric oxide, should 

also be safely stored out of the reach of children. 

You should check to see if any medicines or herbal 

remedies that you or your child use contain 

mercury. Some traditional Chinese and Hispanic 

remedies for stomach disorders (for example, herbal 

balls) contain mercury, and if you give these 

remedies to your children, you may harm them. If 

you are pregnant or nursing a baby and you use 

mercury-containing ethnic or herbal remedies, you 

could pass some of the mercury to your unborn 

child or nursing infant. 

If you use metallic mercury or azogue in religious 

practices, you may expose your children or unborn 

child to mercury or contaminate your home. Such 

practices in which mercury containing substances 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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PUBLIC HEALTH STATEMENT 

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have traditionally been used include Santeria (a 

Cuban-based religion whose followers worship both 

African deities and Catholic saints), Voodoo (a 

Haitian-based set of beliefs and rituals), Palo 

Mayombe (a secret form of ancestor worship 

practiced mainly in the Caribbean), or Espiritismo 

(a spiritual belief system native to Puerto Rico). 

Metallic mercury is used in a variety of household 

products and industrial items, including thermostats, 

fluorescent light bulbs, barometers, glass 

thermometers, and some blood pressure measuring 

devices. You must be careful when you handle and 

dispose of all items in the home that contain 

metallic mercury. 

If small amounts of mercury are spilled, be very 

careful cleaning it up. Do not try to vacuum spilled 

metallic mercury. Using a vacuum cleaner to clean 

up the mercury causes the mercury to evaporate into 

the air, creating greater health risks. Trying to 

vacuum spilled metallic mercury also contaminates 

the vacuum cleaner. Also, take care not to step on 

the mercury and track it into other areas of the 

home. Metallic mercury vapors are very toxic and 

have no odor. Do not remain unnecessarily in that 

room, and try not to let metallic mercury contact 

your eyes, skin, or clothing. If you think you have 

been exposed directly to metallic mercury, wash 

yourself thoroughly and discard contaminated 

clothing by placing them in a sealed plastic bag. 

Perhaps the most important thing to remember if 

you break a household thermometer is do not panic. 

The amount of mercury contained in an oral 

thermometer is small and does not present an 

immediate threat to human health. However, if it is 

not properly cleaned up and disposed of, it may 

present a health risk over time, particularly to 

infants, toddlers, and pregnant women. 

If a thermometer breaks on a counter top or 

uncarpeted floor, remove children from the area. 

Mercury is not absorbent, so do not try to wipe or 

blot it up with a cloth or paper towel; that will only 

spread the mercury and break it up into smaller 

beads, making it more difficult to find and remove. 

Instead, clean up the beads of metallic mercury by 

using one sheet of paper to carefully roll them onto 

a second sheet of paper, or by sucking very small 

beads of mercury into an eye dropper. After 

picking up the metallic mercury in this manner, put 

it into a plastic bag or airtight container. The paper 

and eye dropper should also be bagged in a zip-lock 

plastic container. All plastic bags used in the 

cleanup should then be taken outside of the house or 

apartment and disposed of properly, according to 

instructions provided by your local health 

department or environmental officials. Try to 

ventilate the room with outside air, and close the 

room off from the rest of the home. Use fans (that 

direct the air to the outside and away from the 

inside of the house) for a minimum of one hour to 

speed the ventilation. 

If a thermometer breaks and the liquid/metallic 

mercury spills onto a carpeted floor, try to collect 

the mercury beads in the manner described in the 

above paragraph. Depending on the cut or pile of 

the carpeting, however, it may not be possible to 

collect all of the spilled mercury. Regardless, do 

not vacuum. Instead, call your local (county, city, 

or state) health department and tell them of your 

situation. (You may also call the Agency for Toxic 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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Substances and Disease Registry [ATSDR] toll-free 

at 1-888-42-ATSDR [1-888-422-8737] to obtain 

additional guidance, if local assistance cannot be 

obtained.) 

If larger amounts of metallic mercury are found (for 

example, a jar of liquid mercury), it should be 

contained in an airtight container, and you should 

call your local health department for instructions on 

how to safely dispose of it. If the mercury is in an 

open container or the container does not have a lid, 

place a piece of plastic wrap around the top of the 

container to prevent vapors from escaping; then 

wash your hands thoroughly. If a larger amount is 

spilled, leave the area and contact your local health 

department and fire department. Do not simply 

throw metallic mercury away, but instead seek 

professional help. 

ATSDR and EPA strongly recommend against the 

use of metallic (liquid) mercury that is not properly 

enclosed in glass, as it is in thermometers. This 

form of mercury should not be used or stored in 

homes, automobiles, day-care centers, schools, 

offices, or other public buildings. If you notice a 

child with metallic mercury on his or her clothing, 

skin, or hair, call the fire department and let them 

know that the child needs to be decontaminated. 

Metallic or inorganic mercury can be carried into 

the home from a workers' contaminated clothing 

and shoes. Increased exposure to mercury has been 

reported in children of workers who are exposed to 

mercury at work, and increased levels of mercury 

were measured in places where work clothes were 

stored and in some washing machines. The children 

most likely to be exposed to risky levels of mercury 

are those whose parents work in facilities that use 

mercury (for example, a scientific glassware 

manufacturing plant or a chlor-alkali chemical 

plant), but where no protective uniforms or footgear 

are used. In some reported cases in which children 

were exposed in this way, protective clothing was 

used in the workplace by the parent, but work 

gloves, clothes, and boots, which were 

contaminated with mercury, were taken home, thus 

exposing family members. If you have questions or 

concerns about exposure to mercury at work, you 

have a right to obtain information from your 

employer about your safety and health on the job 

without fear of punishment. The Occupational 

Safety and Health Administration (OSHA) requires 

employers to provide Material Safety Data Sheets 

(MSDSs) for many of the chemicals used at the 

workplace. Information on these sheets should 

include chemical names and hazardous ingredients, 

important properties (such as fire and explosion 

data), potential health effects, how you get the 

chemical(s) in your body, how to properly handle 

the materials, and what to do in an emergency. 

Your occupational health and safety officer at work 

can and should tell you whether chemicals you 

work with are dangerous and likely to be carried 

home on your clothes, body, or tools, and whether 

you should be showering and changing clothes 

before you leave work, storing your street clothes in 

a separate area of the workplace, or laundering your 

work clothes at home separately from other clothes. 

Your employer is legally responsible for providing 

a safe workplace and should freely answer your 

questions about hazardous chemicals. Your OSHAapproved state occupational safety and health 

program or OSHA can also answer any further 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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questions you might have, and help your employer 

identify and correct problems with hazardous 

substances. If you would like to make a formal 

complaint about health hazards in your workplace, 

your OSHA-approved state occupational safety and 

health program or OSHA office will listen to your 

complaint and inspect your workplace when 

necessary. 

One way in which people are routinely exposed to 

extremely small amounts of mercury is through the 

gradual (but extremely slow) wearing-away 

process of dental amalgam fillings, which contain 

approximately 50% mercury. The amount of 

mercury to which a person might be exposed from 

dental amalgams would depend on the number of 

amalgams present and other factors. The Centers 

for Disease Control and Prevention (CDC) has 

determined that dental amalgam fillings do not pose 

a health risk, although they do account for some 

mercury exposure to those having such fillings. 

People who frequently grind their teeth or often 

chew gum can add to the small amount of mercury 

normally released from those fillings over time. If 

you are pregnant, the decision of whether to have 

dental amalgam or a non-mercury material used for 

fillings, or whether existing amalgam fillings should 

be repaired or replaced during pregnancy, should be 

made in consultation with your dentist. The 

practice of having all your dental amalgam fillings 

replaced with non-mercury filling materials just to 

remove the possibility of mercury exposure is not 

recommended by ATSDR. In fact, the removal of 

the mercury amalgam fillings would actually expose 

the patient to a greater amount of mercury for a 

while. Other sources of mercury may increase your 

overall exposure, such as the amount of fish 

consumed per week, especially if caught in local 

waters contaminated with mercury or of certain 

species known to be higher in mercury content 

(shark and swordfish), or an exposure to mercury 

from a nearby hazardous waste site or incinerator. 

You or your children may be exposed to 

methylmercury when eating certain types of fish 

caught from contaminated waters, or when eating 

certain types of wildlife from mercury contaminated 

areas. Most states, Native American tribes, and 

U.S. Territories have issued fish and/or wildlife 

advisories to warn people about methylmercury 

contaminated fish and/or wildlife. Most of the 

methylmercury advisories relate to specific types of 

freshwater or saltwater fish or shellfish, or 

freshwater turtles. Each state, Native American 

tribe, or U.S. Territory sets its own criteria for 

issuing fish and wildlife advisories. A fish or 

wildlife advisory will specify which bodies of water 

or hunting areas have restrictions. The advisory 

will tell you what types and sizes of fish or game 

are of concern. The advisory may completely ban 

eating fish or tell you to limit your meals of a 

certain type of fish. For example, an advisory may 

tell you to eat a certain type of fish no more than 

once a month; or an advisory may tell you to eat 

only certain parts of fish or game, or how to prepare 

it to decrease your exposure to methylmercury. The 

fish or wildlife advisory may be stricter to protect 

pregnant women, nursing women, and young 

children. To reduce your children's exposure to 

methylmercury, you should follow the instructions 

recommended in the fish or wildlife advisories. 

Information on Fish and Wildlife Advisories in your 

state is available from your state public health or 

natural resources department. Signs may also be 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

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posted in certain fishing and hunting areas with 

information about contaminated fish or wildlife. 

FDA currently advises that pregnant women and 

women of childbearing age who may become 

pregnant limit their consumption of shark and 

swordfish to no more that one meal per month. 

This advice is given because methylmercury levels 

are relatively high in these fish species. Women of 

childbearing age are included in this advice because 

dietary practices immediately before the pregnancy 

could have a direct bearing on fetal exposure during 

pregnancy, particularly during the earlier months of 

pregnancy. 

FDA further advises that persons other than 

pregnant women and women of childbearing age in 

the general population limit their regular 

consumption of shark and swordfish (which 

typically contains methylmercury around 1 ppm) to 

about 7 ounces per week (about one serving) to stay 

below the acceptable daily intake for 

methylmercury. For fish species with 

methylmercury levels averaging 0.5 ppm, regular 

consumption should be limited to 14 ounces per 

week. Recreational and subsistence fishers who eat 

larger amounts of fish than the general population 

and routinely fish the same waterbodies may have a 

higher exposure to methylmercury if these waters 

are contaminated. People who consume greater 

than 100 grams of fish (approximately 3.5 ounces) 

every day are considered high-end consumers. This 

is over 10 times more than the amount of fish 

consumed by members of the general population 

(6.5 g/day). No consumption advice is necessary 

for the top ten seafood species that make up about 

80% of the seafood sold in the United States: 

canned tuna, shrimp, pollock, salmon, cod, catfish, 

clams, flatfish, crabs, and scallops. The 

methylmercury in these species is generally less 

than 0.2 ppm, and few people eat more than the 

suggested weekly limit of fish (i.e., 2.2 pounds). 

If you are concerned about a mercury exposure or 

think that you or your child are experiencing the 

adverse effects of mercury, you should consult with 

a doctor or public health official who is familiar 

with the health effects of mercury. 

1.8 IS THERE A MEDICAL TEST TO 

DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO MERCURY? 

There are reliable and accurate ways to measure 

mercury levels in the body. These tests all involve 

taking blood, urine, or hair samples, and must be 

performed in a doctor's office or in a health clinic. 

Nursing women may have their breast milk tested 

for mercury levels, if any of the other samples 

tested are found to contain significant amounts of 

mercury. Most of these tests, however, do not 

determine the form of mercury to which you were 

exposed. Mercury levels found in blood, urine, 

breast milk, or hair may be used to determine if 

adverse health effects are likely to occur. Mercury 

in urine is used to test for exposure to metallic 

mercury vapor and to inorganic forms of mercury. 

Measurement of mercury in whole blood or scalp 

hair is used to monitor exposure to methylmercury. 

Urine is not useful for determining whether 

exposure has occurred to methylmercury. Levels 

found in blood, urine, and hair may be used together 

to predict possible health effects that may be caused 

by the different forms of mercury. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

Blood and urine levels are used as markers to 

determine whether someone has been exposed to 

mercury. They are used to determine whether 

exposure to mercury has occurred and to give a 

rough idea of the extent of exposure, but they do not 

tell exactly how much exposure has occurred. 

Except for methylmercury exposures, blood is 

considered useful if samples are taken within a few 

days of exposure. This is because most forms of 

mercury in the blood decrease by one-half every 

three days if exposure has been stopped. Thus, 

mercury levels in the blood provide more useful 

information after recent exposures than after longterm exposures. Several months after an exposure, 

mercury levels in the blood and urine are much 

lower. Hair, which is considered useful only for 

exposures to methylmercury, can be used to show 

exposures that occurred many months ago, or even 

more than a year ago if the hair is long enough and 

careful testing methods are used. After short-term 

exposures to metallic mercury, mercury vapor can 

be detected in the breath, but this occurs to a 

significant extent only within a few days after 

exposure, and is not a method normally used to 

determine if mercury exposure has occurred. 

1.9 WHAT RECOMMENDATIONS HAS THE 

FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH? 

The federal government develops regulations and 

recommendations to protect public health. 

Regulations can be enforced by law. Federal 

agencies that develop regulations for toxic 

substances include the Environmental Protection 

Agency (EPA), the Occupational Safety and Health 

Administration (OSHA), and the Food and Drug 

Administration (FDA). Recommendations, on the 

other hand, provide valuable guidelines to protect 

public health, but cannot be enforced by law. 

Federal organizations that develop 

recommendations for toxic substances include the 

Agency for Toxic Substances and Disease Registry 

(ATSDR) and the National Institute for 

Occupational Safety and Health (NIOSH). 

Regulations and recommendations can be expressed 

in not-to-exceed levels in air, water, soil, or food 

that are usually based on levels that affect animals; 

then they are adjusted to help protect people. 

Sometimes these not-to-exceed levels differ among 

federal organizations because of different exposure 

times (an 8-hour workday or a 24-hour day), the use 

of different animal studies, or other factors. 

Recommendations and regulations are also 

periodically updated as more information becomes 

available. For the most current information, check 

with the federal agency or organization that 

provides it for the substance in which you are 

interested. Some regulations and recommendations 

for mercury include the following: 

EPA and FDA have set a limit of 2 parts inorganic 

mercury per billion (ppb) parts of water in drinking 

water. EPA is in the process of revising the Water 

Quality Criteria for mercury. EPA currently 

recommends that the level of inorganic mercury in 

rivers, lakes, and streams be no more than 144 parts 

mercury per trillion (ppt) parts of water to protect 

human health (1 ppt is a thousand times less than 1 

part per billion, or ppb). EPA has determined that a 

daily exposure (for an adult of average weight) to 

inorganic mercury in drinking water at a level up to 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

__________________________________________________________________________________________ 

 

 

PUBLIC HEALTH STATEMENT 

MERCURY 

CAS#: 7439-97-6 

Division of Toxicology March 1999 

2 ppb is not likely to cause any significant adverse 

health effects. FDA has set a maximum permissible 

level of 1 part of methylmercury in a million parts 

(ppm) of seafood products sold through interstate 

commerce (1 ppm is a thousand times more than 1 

ppb). FDA may seize shipments of fish and 

shellfish containing more than 1 ppm of 

methylmercury, and may seize treated seed grain 

containing more than 1 ppm of mercury. 

OSHA regulates levels of mercury in the workplace. 

It has set limits of 0.1 milligrams of mercury per 

cubic meter of air (mg/m3) for organic mercury and 

0.05 mg/m3 for metallic mercury vapor in 

workplace air to protect workers during an 8-hour 

shift and a 40-hour work week. NIOSH 

recommends that the amount of metallic mercury 

vapor in workplace air be limited to an average 

level of 0.05 mg/m3 during a 10-hour work shift. 

1.10 WHERE CAN I GET MORE 

INFORMATION? 

If you have any more questions or concerns, please 

contact your community or state health or 

environmental quality department or: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop F-32 

Atlanta, GA 30333 

Information line and technical assistance: 

Phone: 888-422-8737 

FAX: (770)-488-4178 

ATSDR can also tell you the location of 

occupational and environmental health clinics. 

These clinics specialize in recognizing, evaluating, 

and treating illnesses resulting from exposure to 

hazardous substances. 

To order toxicological profiles, contact: 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

Phone: 800-553-6847 or 703-605-6000 

Reference 

Agency for Toxic Substances and Disease Registry 

(ATSDR). 1999. Toxicological profile for mercury. 

Atlanta, GA: U.S. Department of Health and 

Human Services, Public Health Service. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov