Overview
Mercury 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.
Compounds which contain mercury in combination
with non-carbon substances such as chlorine,
oxygen, or sulfur are called inorganic mercuries.
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
mercury in air, which eventually falls back to
earth into bodies of water. Mercury in water
accumulates in fish as the water passes over
their gills. 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.
Occasional exposures to mercury can also occur
by contact with broken household items such as
thermometers.
The effects of mercury on unborn children
have been documented in accidental poisonings
and scientific studies. During the 1950's, large
amounts of organic mercury were dumped into the
Minamata Bay in Japan, and fish containing high
mercury levels were eaten by many pregnant
women. Many of the children born to those women
had severe nerve damage, which was later
referred to as Fetal Minamata Disease. In Iraq,
children born to mothers who ate grain
contaminated with organic mercury may have
learned to walk at a later age. In the Faroe
Islands, where mercury exposure occurs primarily
by eating whale meat, children born to mothers
with higher body levels of mercury scored lower
on brain function tests. However, no effects
were seen in children of the Seychelles Islands,
where residents are exposed to mercury by eating
fish 12 times a week.
The Food and Drug Administration (FDA)
recommends that pregnant women and women of
child bearing age reduce their exposure to
mercury by avoiding certain types of fish
containing significant levels of mercury such as
swordfish, shark, and the large types of tuna
used to make sushi or steaks. The FDA also
recommends that pregnant woman and woman of
child bearing age eat swordfish or shark no more
than once per month.
Another 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 that there was no evidence
indicating that amalgams in pregnant women are
harmful to unborn children, but suggested
avoiding the use or removal of amalgams in
pregnant women as a safety measure.
In order to better characterize mercury
emissions from coal-burning power plants, the
Environmental Protection Agency (EPA) will soon
require power plants with 25 megawatts capacity
and greater to test and report mercury levels in
coal. In addition, 75 plants, selected at
random, will be required to measure the level of
mercury in their smokestacks.
Some 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 also be
avoided by properly cleaning spills from items
such as broken thermometers. Skin contact should
be avoided and the mercury should be placed into
a vial which should then be tightly capped and
disposed.
The California Environmental Protection
Agency (Cal/EPA) has classified mercury,
methylmercury, and mercury compounds as
developmental toxins, which means there is
evidence that the 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 pbb) 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).
Description
of Mercury
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 September 1995).
Sources
of Mercury Exposure
People can be exposed to mercury by breathing
in air, eating food, or drinking water that is
contaminated with mercury compounds. Mercury can
also enter the body through contact with the
skin.
Mercury is released to 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 to 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. The 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 rituals.
Levels
of Mercury in the Body
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 September 1995).
Body 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).
Mercury
Health Effects in Unborn Children
According to ATSDR, "Exposure to high
levels of metallic, inorganic, or organic
mercury can permanently damage the brain,
kidneys, and developing fetus" (ATSDR
ToxFAQ September 1995). 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
mother"(FDA
Consumer, September 1994). The health
effects of mercury on unborn children were
observed in accidental poisonings and studies of
individuals who ate large amounts of seafood, a
common source of mercury.
In the 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).
The 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 then 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.
From an 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)
The 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.
The 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 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).
Reviews of the Faroe Islands and Seychelles
Islands studies continue and scientists are
trying to determine why different results may
have been 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
contains PCBs, which may have affected study
results. However, scientists did take this into
account when evaluating the study results (NIEHS
PR #24-97, November 1997)
Mercury in Fish
Mercury levels in fish are expressed in terms
of parts per million (ppm), which is equivalent
to 1 part mercury per 1 million parts fish.
According to the FDA (FDA
Consumer, September 1994),
Fish 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.
Methyl 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 are
elevated.
The FDA has stated (FDA
Consumer, September 1994),
Fish is an important source of
high-quality protein, vitamins and minerals.
FDA seafood specialists say that eating a
variety of types of fish, the normal pattern
of consumption, does not put any one in
danger of mercury poisoning. It is when
people eat fad diets - frequently eating
only one type of food or a particular
species of fish - that they put themselves
at risk. Pregnant women and women of
childbearing age, who may become pregnant,
however, are advised by FDA experts, to
limit their consumption of shark and
swordfish to no more than once a month.
These fish have much higher levels of methyl
mercury than other commonly consumed fish.
Since the fetus may be more susceptible than
the mother to the adverse effects of methyl
mercury, FDA experts say that it is prudent
to minimize the consumption of fish that
have higher levels of methyl mercury, like
shark and swordfish. This advice covers both
pregnant women and women of childbearing age
who might become pregnant, since the first
trimester of pregnancy appears to be the
critical period of exposure for the fetus.
Dietary practices immediately before
pregnancy would have a direct bearing on
fetal exposure during the first trimester,
the period of greatest concern. Consumption
advice is unnecessary for the top 10 seafood
species, making up about 80 percent of the
seafood market--canned tuna, shrimp, pollock,
salmon, cod, catfish, clams, flatfish,
crabs, and scallops. This is because the
methyl mercury levels in these species are
all less than 0.2 ppm and few people eat
more than the suggested weekly limit of fish
(2.2 pounds) for this level of methyl
mercury contamination.
The FDA 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."
For fish caught by sports fishermen, (FDA
Consumer, September 1994), FDA recommends
checking "with state or local governments
for advisories about water bodies or fish
species. These advisories provide up-to-date
public health information on local areas and
warn of areas or species where mercury (or other
contamination) is of concern."
Mercury
in Dental Amalgams (Fillings)
Dental 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):
The 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."
The 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.
Mercury
from Burning of Coal by Power Plants
According to EPA (EPA
Press Release 11/16/98), "Utilities are
the largest source of mercury emissions into the
air, with one third of all U.S. man-made
emissions coming from coal-fired plants
(virtually no mercury is emitted from any other
type of power plant fuel)". Emissions from
these plants do not only affect air levels of
mercury, but also bodies of water and fish that
may be caught in those waters. The EPA (EPA
Press Release 11/16/98) has stated,
"Mercury air emissions can end up in
waterways through rainfall and runoff and
bioaccumulate, or build up, in the food chain.
Mercury is the most frequent cause of fish
consumption warnings issued by states. Forty
states to date have issued fish consumption
advisories in at least one body of water.
Subsistence fishers and women of child-bearing
age particularly are advised to pay careful
attention to such warnings posted by
states."
The EPA has stated in a press release (EPA
Press Release 11/16/98) that it "will
soon send letters to utility companies requiring
all coal-fired power plants above 25 megawatts
generating capacity (approximately 1400 plants
nationwide) to sample and test for mercury
content of the coal they burn and report the
results of the testing to the Agency. EPA will
also require a sample of 75 plants (randomly
selected to include the major types of coal and
pollution controls, e.g. scrubbers) to perform
smokestack testing for the amount and type of
mercury emissions. EPA will then make the
results of these tests available to the public.
EPA will begin collecting the emissions data
Jan. 1, 1999, and start making it available to
the public on the Internet early in the year
2000."
Mercury
in Religious Practices
The 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 Exposure):
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.
The 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 devotional candles.
Mercury
Spills in Households
The following information about cleaning
small household mercury spills is taken from the
Louisiana Department of Environmental Quality
web page (Louisiana
Department of Environmental Quality, September
15, 1998):
Mercury can be found in some
over-the-counter thermometers and fluorescent
light bulbs. In the event that one is broken
and the mercury escapes, remove all jewelry,
especially gold. Handle the mercury by raking
it, with a cardboard or similar object, into a
container such as a medicine bottle or vial.
Place the cap tightly on the container and
re-enforce with tape. The container of mercury
can then be disposed into the municipal
dumpster for pickup.
Keep any objects containing mercury out of
the reach of children. If any objects are in
contact with the mercury, clean them and the
contaminated area thoroughly with the
appropriate cleanser.
Please be advised that if any mercury
should contaminate gold jewelry, the items
must be taken to a jeweler to have them
professionally cleaned.
Also, while handling mercury, or any other
hazardous substance, one should always wear
protective gloves. In the event that mercury
is in contact with the skin, wash the area(s)
thoroughly and immediately with soap and warm
water.
A vacuum cleaner should never be used to
clean mercury spills. According to ATSDR (ATSDR
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
cleaner."
Federal
and State Government Regulatory Limits
The 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).
The following are government limits (Agency
for Toxic Substances and Disease Registry (ATSDR)
ToxFAQs, September 1995):
The 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.
The Food and Drug Administration (FDA) has
set a maximum permissible level of 1 part of
methylmercury in a million parts of seafood (1
ppm).
The 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.
The EPA is proposing a mercury limit for fish
that is lower than the one established by the
FDA (EHP,
Volume 104(8), August 1996). The EPA level
is recommended to protect the public health as
well as fish-eating animals such as birds. The
FDA has expressed concerns about the impact that
the lower EPA mercury limit would have on the
public and industry.
Agencies
to Contact for More Information
Agency for Toxic Substances and Disease
Registry
Division of Toxicology
1600 Clifton Road, E-29
Atlanta, Georgia 30333
ATSDR Information Center / ATSDRIC@cdc.gov
/ 1-800-447-1544
FDA invites consumers who have questions
about methyl mercury in fish or other seafood
concerns to telephone the 24-hour FDA Seafood
Hotline at (1-800) FDA-4010 or (202) 205-4314
(in the Washington, D.C., area). The automated
hot line and Flash Fax service are available 24
hours a day. Public affairs specialists can be
reached at the same numbers from noon to 4 p.m.
Eastern time, Monday through Friday.
More information about testing of mercury
emissions from power plants can be obtained
from:
US
Environmental Protection Agency. For
further technical information, contact William
Maxwell of EPA's Office of Air Quality Planning
and Standards at 919-541-5430 or e-mail him at: maxwell.bill@epa.gov."
Dental
Information 
