Safety > Issues of Interest > Thimerosal
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.
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.
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
sulfide (also known as cinnabar) which
is red and turns black after exposure
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.
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. Thimerosal is an
organic mercury compound that is metabolized
to ethylmercury and thiosalicylate
more information on mercury go to http://www.atsdr.cdc.gov/toxprofiles/phs46.html
are recommended limits
for mercury exposure established?
Federal agencies, including the Agency
for Toxic Substances and Disease Registries
(ATSDR), the Food and Drug Administration
(FDA), and the Environmental Protection
Agency (EPA), have established guidelines
for levels of mercury exposure that
are thought to be safe.
Federal safety standards for
mercury are based on research that
has been performed on methylmercury.
There are more data on methylmercury
than on a related form called ethylmercury
because methylmercury is more easily
bound to tissue than ethylmercury,
and remains there a longer time.
Methylmercury is also believed
to be more toxic than ethylmercury
(Magos, 2001) and is the form of mercury
of greatest public health concern (Mahaffey,
limits on methylmercury exposure are
not “set lines” below which there is
safety and above which adverse health
effects will immediately occur (Mahaffey,
1999). There is a significant safety margin incorporated
into all acceptable mercury exposure
guidelines are meant to be starting
points for evaluation of mercury exposure,
and should not be viewed as absolute
levels above which harm can be expected
happens if your exposure
exceeds the recommended levels?
nervous system is very sensitive to
all forms of mercury.
Methylmercury and metal vapors
are often more harmful than other forms,
because more mercury in these forms
reaches the brain. Exposure to high
levels of metallic, inorganic, or organic
mercury can permanently damage the
brain, kidneys, and developing fetus.
Effects on brain functioning may include
irritability, shyness, tremors, changes
in vision or hearing, attention, language,
and memory problems.
of short-term exposure to high levels
of metallic mercury vapors may include
lung damage, nausea, vomiting, diarrhea,
increases in blood pressure or heart
rate, skin rashes, and eye irritation.
is important to keep in mind that being
exposed to more than the recommended
mercury limits does not necessarily
mean you will experience adverse health
There is a significant safety
margin incorporated into all acceptable
mercury exposure limits; they should
not be viewed as absolute levels above
which harm can be expected to occur.
is most vulnerable
babies (developing fetus) are more
sensitive to the effects of many chemicals,
Premature babies are also more
vulnerable because they tend to be
very small and their brain is not as
developed as that of a full-term
baby. Children may be at higher risk
of mercury exposure than are adults
because they eat more per pound of
body weight and because they may be
inherently more sensitive than adults,
since their nervous systems are still
Thus, the Food and Drug Administration
(FDA) and Environmental Protection
Agency (EPA) are advising women who
are pregnant or may become pregnant,
nursing mothers, and young children
avoid some types of fish and eat fish
and shellfish that are lower in mercury.
For more information consult the Joint
Federal Advisory for Mercury in Fish
can mercury affect children?
young children are more sensitive to
mercury than adults.
Mercury in the mother's body
passes to the fetus and can pass to
a nursing infant through breast milk.
However, the benefits of breastfeeding
may be greater than the possible adverse
effects of mercury in breast milk.
a pregnant woman ingests mercury at
high levels, harmful effects that may
be passed from the mother to the developing
fetus include brain damage, mental
retardation, lack of coordination,
blindness, seizures, and an inability
to speak. Children poisoned by mercury
may develop nervous and digestive system
problems and kidney damage.
is a very effective preservative that
has been used in some vaccines and
other products since the 1930’s. Thimerosal
contains approximately 49% ethylmercury.
There is no evidence of harm caused
by the low doses of thimerosal in vaccines,
except for minor reactions like redness
and swelling at the injection site.
However, in July 1999 the Public Health
Service (PHS) agencies, the American
Academy of Pediatrics (AAP), and vaccine
manufacturers agreed that thimerosal
should be reduced or eliminated in
vaccines as a precautionary measure.
Today, of all routinely recommended
licensed pediatric vaccines that are
currently being manufactured for the
U.S. market, only some influenza (flu)
vaccines and tetanus-diphtheria (Td)
vaccine (given to children age 7 and
older) contain thimerosal as a preservative;
the remaining pediatric vaccines do
not contain thimerosal as a preservative.
the mercury in thimerosal (ethylmercury)
the same as the kind found in certain
Thimerosal is a very effective preservative
that contains a form of mercury called
ethylmercury. Thimerosal contains approximately
49% ethylmercury. Thimerosal has been
used in some vaccines and other products
since the 1930's to help keep them
safe from bacterial contamination.
In contrast, methyl mercury is an environmental
contaminant. In March 2004, the Food
and Drug Administration (FDA) and the
Environmental Protection Agency (EPA)
released a joint advisory for the consumption
of fish for women who may become pregnant,
pregnant women, nursing mothers, and
young children. The advisory is based
on an EPA standard of 0.1 mcg/kg per
day of methylmercury which is not a
component of thimerosal.
to main thimerosal page