is a metal found in various forms. Metallic mercury is the silver colored
liquid used in thermometers. Mercury combined with carbon is called organic
mercury; methyl mercury is a common example of an organic mercury. Mercury
compounds which contain non-carbon substances such as chlorine, oxygen, or
sulfur are called inorganic mercurials. Mercury occurs naturally in the
environment, and the levels are increased by certain human activities such
as the burning of coal by power plants. Burning coal increases the amount of
airborne mercury, which eventually falls back to earth into bodies of water.
Mercury in water accumulates in fish. Common ways in which people are
exposed to mercury include breathing contaminated air, eating contaminated
fish, and through the use of mercury based amalgams (fillings) in dental
treatments. Mercury can also enter the body through direct skin contact, and
exposures to mercury may occur by contact with broken household items such
effects of mercury on unborn children have been documented in cases of
accidental poisonings and in scientific studies. During the 1950's, large
amounts of organic mercury were dumped into Minamata Bay in Japan, and
mercury-contaminated fish were eaten by many pregnant women. Many of the
children born to those women had severe nervous system damage, which was
later referred to as Fetal Minamata Disease. In Iraq, studies showed that
children born to mothers who ate grain contaminated with organic mercury may
have learned to walk at a later age than non-exposed children. In the Faroe
Islands, where mercury exposure occurs by eating contaminated whale meat,
children born to mothers with higher body levels of mercury scored lower on
brain function tests than children born to mothers with lower body levels of
mercury. In contrast, no adverse effects were seen in children of the
Seychelles Islands, where residents are routinely exposed to mercury by
eating fish 12 times a week.
Food and Drug Administration (FDA) and Environmental Protection Agency (EPA)
recommend that young children and women who are pregnant, could become
pregnant, or are nursing reduce their exposure to mercury by not eating fish
containing high levels of mercury such as swordfish, shark, king mackerel,
and tilefish. The FDA and EPA state that women and children can eat up to 12
ounces (2 average meals) per week of fish containing lower levels of
mercury, such as shrimp, canned light tuna, salmon, Pollock, and catfish.
Because albacore tuna contains higher levels of mercury, it is recommended
that not more than 6 ounces be eaten per week.
possible source of mercury exposure to unborn children is the use of dental
amalgams (mercury-based fillings) in pregnant women. Some special interest
groups in the U.S. have attempted to place limits on the use of these
amalgams. However, the U.S. Public Health Service and the FDA have taken the
position that there is no scientific evidence to support limiting the use of
mercury-based amalgams at this time. Similar conclusions were also reached
by the World Health Organization and the government of New Zealand. German
and Canadian governments concluded there was no evidence indicating that
amalgams in pregnant women are harmful to unborn children, but suggested
avoiding the use of, or even removing amalgams in pregnant women as a safety
is proposing national standards for hazardous air pollutants and intends to
require lower emissions of mercury and other pollutants from coal and
oil-fired utility plants (EPA
individuals may also be exposed to mercury through religious practices.
According to a health alert issued by the Agency of Toxic Substances and
Disease Registry (ATSDR), mercury may be sprinkled around homes or cars by
practitioners of religions such as Esperitismo, Santeria, or Voodoo. Broken
thermometers may also be a source of mercury exposure in homes. Household
exposures to mercury can be minimized by properly cleaning spills from items
such as broken thermometers. Skin contact should be avoided and the spilled
mercury should be placed into a vial which should then be tightly capped and
properly disposed of.
California Environmental Protection Agency (Cal/EPA) has classified mercury,
methylmercury, and mercury compounds as developmental toxicants, which means
there is evidence that these compounds can be harmful to unborn children.
Acceptable levels of mercury have been established by other regulatory
agencies. A limit of 2 parts mercury per billion parts of drinking water (2
ppb) has been established by the EPA. In addition, the EPA requires the
reporting of spills or releases of 1 pound or more of mercury. The FDA has
set a limit of 1 part per million (ppm) of mercury in seafood. The FDA also
regulates the use of mercury in medical treatments such as dental amalgams.
The Occupational Safety and Health Administration (OSHA) limits the level of
mercury in workplaces to 1 milligram per 10 cubic meters of air (1 mg/10 m3).
According to the Agency of Toxic Substances and Disease Registry (ATSDR),
"Mercury is a naturally occurring metal which has several forms. The
metallic mercury is a shiny, silver-white, odorless liquid. If heated, it is
a colorless, odorless gas. Mercury combines with other elements, such as
chlorine, sulfur, or oxygen, to form inorganic mercury compounds or 'salts.'
Most inorganic mercury compounds are white powders or crystals. Mercury also
combines with carbon to make organic mercury compounds. The most common
organic mercury compound is methylmercury. Methylmercury is produced mainly
by small organisms in the water and soil, but more mercury in the
environment can increase the levels of methylmercury that these small
organisms make" (ATSDR
ToxFAQ April 1999).
can be exposed to mercury by breathing in air, eating food, or drinking
water contaminated with mercury compounds. Mercury can also enter the body
through contact with the skin.
is released into the air from natural sources like volcanoes and off-gassing
from the earth's crust and bodies of water (EHP,
Volume 104(8), August 1996). Mercury can also be released into the air
through the incineration of waste, the burning of coal by power plants, and
by industries that use mercury to manufacture products. Mercury in the air
eventually falls back to earth and accumulates in bodies of water. Fish
absorb mercury through their gills and by eating contaminated food sources.
Mercury becomes most concentrated in fish that eat smaller fish.
Exposure to mercury is also possible through dental amalgams (fillings),
which contain 50 percent mercury. Occasional exposure to mercury can also
occur from broken thermometers. Lastly, practitioners of certain religions,
such as Esperitismo, Santeria, or Voodoo have been known to use mercury in
According to ATSDR, "Tests are available to measure mercury levels in the
body. Blood or urine samples are used to test for exposure to metallic
mercury and to inorganic forms of mercury. Measurement of mercury in whole
blood or in scalp hair is used to measure exposure to methylmercury. Your
doctor can take samples and send them to a testing laboratory" (ATSDR
ToxFAQ April 1999).
levels of mercury are often expressed in terms of parts per million (ppm), 1
part of mercury per million parts of body tissue. As an example, a hair
concentration of 1 ppm mercury is equal to 1 milligram of mercury per
kilogram of hair. In people who have not been exposed to high levels of
mercury, the average level of mercury in the hair is 2 ppm (FDA
Consumer, September 1994).
According to ATSDR, "Exposure to high levels of metallic, inorganic, or
organic mercury can permanently damage the brain, kidneys, and developing
ToxFAQ April 1999). FDA toxicologist, Dr. Mike Bolger, stated that
"Methyl mercury easily crosses the placenta, and the mercury concentration
rises to 30 percent higher in fetal red blood cells than in those of the
Consumer, September 1994). The adverse health effects of mercury on
unborn children were observed in cases of accidental poisonings and in
studies of individuals who ate large amounts of seafood, a common source of
1950's, large of amounts of organic mercury were released into the Minamata
Bay in Kyushu, Japan (Environmental
Health Perspectives, Volume 104, April 1996). Many individuals who ate
mercury-contaminated fish and shellfish from the bay developed severe damage
to the nervous system and many eventually died. Symptoms caused by the
mercury poisoning were referred to as Minamata Disease. Fetal Minamata
Disease developed in about 7% of children whose mothers ate contaminated
fish while pregnant. Symptoms of Fetal Minamata Disease include
uncoordinated movements, abnormal reflexes, speech problems, and seizures.
Fetuses were found to be much more sensitive to mercury than were their
mothers. The nervous systems of some mothers of children with Fetal Minamata
Disease were only mildly affected; a common symptom was a narrowing of the
visual field. The level of mercury in the mothers who gave birth to affected
children after eating mercury-contaminated fish is not certain, but
generally, nerve damage was seen in adults with mercury levels in hair of 50
ppm or higher (EHP,
Volume 104(8), August 1996).
following excerpt describes a case of accidental mercury poisoning in Iraq (FDA
Consumer, September 1994):
Studies of the poisoning incident in Iraq have provided limited data about
what effects low levels of methyl mercury exposures to the fetus have on the
infant. One possible effect, for example, is lateness in walking. In the
fall and winter of 1971-72, wheat seed intended for planting--and which had
therefore been treated with an alkyl mercury fungicide--was mistakenly used
to prepare bread; more than 6,500 Iraqis were hospitalized with neurological
symptoms and 459 died. The vast majority of the mothers experienced
exposures that resulted in hair levels greater than the lowest levels
associated with effects in adults. But there was no clear evidence that the
fetus was more sensitive than the adult to methyl mercury.
analysis of the Iraqi poisoning case, it was estimated that there is about a
5% chance that fetuses could be affected if their mothers have a hair level
of 10-20 ppm mercury (EHP,
Volume 104(8), August 1996)
U.S. National Institute of Environmental Health Sciences (NIEHS) and the
European Commission sponsored a mercury health study in the Faroe Islands in
the North Atlantic. People on these islands are exposed to mercury mainly by
eating whale meat (NIEHS
PR #24-97, November 1997). Pregnant women in the study had hair mercury
levels of 10-20 ppm (EHP,
Volume 107(1), January 1999). To determine the effects of mercury intake
by pregnant women, 7-year-old children were tested for brain function by
measuring their attention span, memory, and speaking ability. Children born
to mothers who had higher concentrations of mercury in their hair and
umbilical cords scored lower on the brain function tests. Professor Roberta
F. White of Boston University looked at the study results and concluded that
"Several domains of brain function may be affected by prenatal methylmercury
exposure. Most of the results remained within normal ranges, but any
developmental delay in young children may be a concern.
NIEHS also sponsored a study to examine the effects of mercury on unborn
children from the Seychelles Islands in the Indian Ocean (NIEHS,
February 7, 1996). The residents of the islands eat fish about 12 times
a week and the average concentration of mercury in the hair of women is 10
ppm. However, some woman had hair levels of mercury as high as 36 ppm.
Children were tested for mental and physical ability from the ages of 6
months to five years. The researchers concluded that "Cognitive
developmental outcomes up to 2 years of age appear essentially normal
following intrauterine exposure to a maternal hair mercury level of about 6
ppm through maternal fish consumption." They went on to say that "although
data at older ages is [sic] needed, the results available so far indicate
that low-level mercury exposure from eating fish during pregnancy shows no
harmful effect." Philip Davidson of the University of Rochester stated, "If
somebody who eats fish twice a day does not show effects from mercury
exposure, it's unlikely that somebody who eats fish twice a week will be
affected, and the fish they eat in the Seychelles contains the same amount
of mercury as fish sold at supermarkets and eaten in the United States" (NIEHS
Center Program, September 1998).
of the Faroe Islands and Seychelles Islands studies are continuing as
scientists try to determine why different results were obtained. One
scientific panel concluded that discrepancies may have resulted from dietary
differences or ethnic variability (EHP
Volume 107(1), January 1999). The whale meat eaten by residents of the
Faroe Islands also contained PCBs, which may have affected study results.
However, scientists did take this into account when evaluating the Faroe
Islands study results (NIEHS
PR #24-97, November 1997).
levels in fish are expressed in terms of parts per million (ppm), which is
equivalent to 1 part mercury per 1 million parts fish (1 mg mercury/kg
fish). According to the FDA (FDA
Consumer, September 1994),
absorb methyl mercury from water as it passes over their gills and as they
feed on aquatic organisms. Larger predator fish are exposed to higher levels
of methyl mercury from their prey.
mercury binds tightly to the proteins in fish tissue, including muscle.
Cooking does not appreciably reduce the methyl mercury content of the fish.
Nearly all fish contain trace amounts of methyl mercury, some more than
others. In areas where there is industrial mercury pollution, the levels in
the fish can be quite elevated. In general, however, methyl mercury levels
for most fish range from less than 0.01 ppm to 0.5 ppm. It's only in a few
species of fish that methyl mercury levels reach FDA limit for human
consumption of 1 ppm. This most frequently occurs in some large predator
fish, such as shark and swordfish. Certain species of very large tuna,
typically sold as fresh steaks or sushi, can have levels over 1 ppm. (Canned
tuna, composed of smaller species of tuna such as skipjack and albacore, has
much lower levels of methyl mercury, averaging only about 0.17 ppm.) The
average concentration of methyl mercury for commercially important species
(mostly marine in origin) is less than 0.3 ppm. Spot-caught predator
fresh-water species like pike and walleye sometimes have methyl mercury
levels in the 1 ppm range. Other fresh-water species also have elevated
levels, particularly in areas where mercury levels in the local environment
recent consumer advisory, The FDA and EPA state (FDA
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. So, women and young children in particular should include
fish or shellfish in their diets due to the many nutritional benefits.
However, nearly all fish and
shellfish contain traces of mercury. For most people, the risk from mercury
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 mercury in fish and
shellfish depend on the amount of fish and shellfish eaten and the levels of
mercury in the fish and shellfish. Therefore, the Food and Drug
Administration (FDA) and the Environmental Protection Agency (EPA) are
advising women who may become pregnant, pregnant women, nursing mothers, and
young children to avoid some types of fish and eat fish and shellfish that
are lower in mercury.
To reduce exposure to mercury while obtaining benefits of eating
fish, the FDA and EPA recommend that women and children
1. Do not eat Shark, Swordfish, King Mackerel, or Tilefish because they
contain high levels of mercury.
2. Eat up to 12 ounces (2 average meals) a week of a variety of fish and
shellfish that are lower in mercury.
Five of the most
commonly eaten fish that are low in mercury are shrimp, canned light tuna,
salmon, pollock, and catfish.
eaten fish, albacore tuna has more mercury than canned light tuna.
So, when choosing your two meals of fish and shellfish, you may eat up to 6
ounces (one average meal) of albacore tuna per week.
fish caught by sports fishermen (FDA
2004) FDA and EPA state, "Check local advisories about the safety of
fish caught by family and friends in your local lakes, rivers, and coastal
areas. If no advice is available, eat up to 6 ounces (one average meal) per
week of fish you catch from local waters, but don't consume any other fish
during that week."
has determined that mercury levels in fish sold in the United States must
not exceed 1 ppm (FDA
Consumer, September 1994). To ensure a safe fish supply (FDA
Consumer, September 1994), "FDA works with state regulators when
commercial fish, caught and sold locally, are found to contain methyl
mercury levels exceeding 1 ppm. The agency also checks imported fish at
ports and refuses entry if methyl mercury levels exceed the FDA limit."
amalgams contain about 50% mercury and there are concerns that unborn
children can be exposed to mercury vapors given off by the amalgams in
mothers. Some special interest groups have tried to ban or limit the use of
mercury based amalgams. In order to investigate this issue, the U.S. Public
Health Service (PHS) assembled a group of scientists from various
governmental agencies. The following excerpts, taken directly from the
report generated in 1993, summarize some of the primary conclusions reached
by the scientists (U.S.
Department of Health and Human Services Public Health Service, January 1993):
Dental amalgam, an inter-metallic compound, contains elemental mercury that
is emitted in minute amounts as vapor. Because vapor emitting from amalgam
restorations can be absorbed by the patient through inhalation, ingestion,
or other means, concerns have been raised about possible toxicity. At
present, there is scant evidence that the health of the vast majority of
people with amalgam is compromised, nor that removing amalgam fillings has a
beneficial effect on health. It also is recognized that a total conversion
from dental amalgam to alternative materials would cause a significant
increase in U.S. health care costs. Nonetheless, the possibility that this
material, as well as currently available alternatives, could pose health
risks cannot be totally ruled out because of the paucity of definitive human
Given the limitations of existing scientific data, a research program should
be designed and implemented to fill as many gaps as possible in current
knowledge about the potential long-term biological effects of dental amalgam
and alternative restorative materials. The PHS should be a leader in this
The PHS should also educate dental personnel and consumers about the risks
and benefits of dental amalgam. An educational program should include
information on all restorative materials to help dentists and their patients
make informed dental treatment decisions, and encourage dental care
providers to report adverse reactions. Such a program should promote the use
of preventive measures such as fluoride and dental sealants to prevent
caries and thus further reduce the need for dental restorations.
The U.S. Public Health Service believes it is inappropriate at this time to
recommend any restrictions on the use of dental amalgam, for several
reasons. First, current scientific evidence does not show that exposure to
mercury from amalgam restorations poses a serious health risk in humans,
except for an exceedingly small number of allergic reactions. Second, there
is insufficient evidence to assure the public that components of alternative
restorative materials have fewer potential health effects than dental
amalgam, including allergic-type reactions. Third, there are significant
efforts underway in the U.S. to reduce the amount of mercury in the
environment. And finally, as stated previously, amalgam use is declining due
to a lessening of the incidence of dental caries and the increasing use of
U.S. Public Health Service reassembled the group in 1997 to discuss new
information published since the original report in 1993. According to the
1997 report (U.S.
Department of Health and Human Services Public Health Service, October 1997),
"In 1997, with input from a broad cross-section of scientists and dental
professionals within USPHS, the FDA completed a review of nearly 60 studies
that were published in peer reviewed scientific literature and were cited by
citizen groups that petitioned the agency for stringent regulatory actions
against dental amalgam. The analysis of the cited studies indicated that the
current body of data does not support claims that individuals with dental
amalgam restorations will experience adverse effects, including neurologic,
renal or developmental effects, except for rare allergic or hypersensitivity
reactions." The FDA concluded that "the agency does not believe there is
scientific justification for discontinuing or curtailing amalgam use."
1997 U.S. Public Health Service Report also discussed opinions of foreign
governments regarding the use of mercury amalgams. According to the report
U.S. Department of Health and Human Services Public Health Service, October
1997, "The governments of Sweden and Denmark have recommended against
the use of mercury-containing materials as part of national environmental
protection initiatives provided that suitable non-amalgam materials are
available. The German government has recommended against the placement of
dental amalgam and dental restorative materials in general in patients with
demonstrated allergy to such materials, as well as patients with severe
renal dysfunction. Germany has also advised against the placement of dental
amalgam and the removal of amalgam fillings in pregnant women as a
precautionary measure while at the same time acknowledging the lack of
evidence that exposure of the unborn to mercury released from the mother's
amalgam fillings causes any health damage to the child. The European
Commission, the governments of Canada, Quebec and New Zealand, and the World
Health Organization have independently evaluated the current body of science
relating to dental amalgam safety and universally concluded that the vast
majority of people treated with dental amalgam are not at risk.
Notwithstanding this conclusion, Canada and its province of Quebec have
recommended prudence in dental intervention therapies for certain patient
sub-populations such as pregnant women."
Research to address health concerns of dental amalgams continues.
following national alert was issued by the Agency of Toxic Substances and
Disease Registry (ATSDR) (ATSDR
National Alert: A Warning About Continuing Patterns of Metallic Mercury
Persons who use metallic mercury in ethnic folk medicine and for religious
practices are at risk. Metallic mercury is sold under the name "azogue" in
stores (sometimes called botanicas), which specialize in religious items
used in Esperitismo (a spiritual belief system native to Puerto Rico),
Santeria (a Cuban-based religion that venerates both African deities and
Catholic saints), and voodoo.
use of azogue in religious practices is recommended in some Hispanic
communities by family members, spiritualists, card readers, and santeros.
Typically, azogue is carried on one's person in a sealed pouch prepared by a
spiritual leader or sprinkled in the home or automobile. Some botanica
owners suggest mixing it in bath water or perfume and placing it in
following information about cleaning small household mercury spills is taken
from the Louisiana Department of Environmental Quality web page
(Louisiana Department of Environmental Quality, 2000):
mercury escapes into the environment, evacuate children and pregnant women.
Remove all jewelry, especially gold. Handle the mercury carefully. Wear
rubber gloves and scoop it onto a sheet of paper or suck it up with an
eyedropper. Place the mercury in a medicine vial or similar airtight
container. The scoop, paper or eyedropper should also be bagged and disposed
properly according to guidance provided by environmental officials or your
local health department. Ventilate the room to the outside and close off the
rest of the home. Use fans for a minimum of one hour to speed the
ventilation. Do not simply throw the mercury away. Seek professional
guidance from local recycling, solid waste or hazardous waste agencies.
Large retailers and building centers may accept glass-encapsulated mercury,
as in thermostats, for recycling.
any objects containing mercury out of the reach of children. Children found
to be playing with liquid mercury or broken fluorescent lamps should be
referred to a physician or poison control center immediately.
Mercury contaminated gold jewelry must be taken to a jeweler to have them
handling mercury, or any other hazardous substance, one should always wear
protective gloves. If mercury contacts with the skin, wash the area(s)
thoroughly and immediately with soap and warm water. If you believe that you
have absorbed mercury though your skin or inhaled mercury vapors, you should
contact your physician or poison control center immediately.
vacuum cleaner should never be used to clean mercury spills. According to
National Alert: A Warning About Continuing Patterns of Metallic Mercury
Exposure), "Using a vacuum cleaner causes metallic mercury to vaporize
in the air, creating greater health risks. It also ruins the vacuum
California Environmental Protection Agency (Cal/EPA) has added methyl
mercury, and mercury compounds to its Proposition 65 list of developmental
toxins. This means there is evidence that the compounds can be harmful to
unborn children (Cal/EPA
Proposition 65 List).
following are government limits (ATSDR ToxFAQs, April 1999):
EPA has set a limit of 2 parts of mercury per billion parts of drinking
water (2 ppb). The EPA requires that discharges or spills of 1 pound or more
of mercury be reported.
Food and Drug Administration (FDA) has set a maximum permissible level of 1
part of methylmercury in a million parts of seafood (1 ppm).
Occupational Safety and Health Administration (OSHA) has set a limit of 1
milligram of mercury per 10 cubic meters of workplace air (1 mg/10 m³) that
should not be exceeded during any part of the workday.