Mercury
Poisoning Exposure
How
are humans exposed to mercury?
Because
mercury
is an element that occurs naturally
and abundantly, people are regularly
exposed to it at low levels. Some
mercury exists in the air as a result
of natural processes, such as erosion
and soil decomposition. Human activities,
such as burning fuel and garbage,
add to the atmospheric mercury. Mercury
is also returned to soil and water
through precipitation. People may
come into contact with mercury in
any of these locations and in any
of mercury's
three forms: metallic, inorganic,
and organic.
- Metallic
mercury is the purest form of
mercury. It is used in thermometers,
batteries, and dental fillings.
Metallic mercury is liquid at room
temperature, but can be dangerous
to breathe if it evaporates.
- Inorganic
mercury is part of a compound
with another element (often chlorine,
oxygen, or sulfur). It is used in
antiseptics and in thimerosal, a
component of some medications and
vaccines. It usually is found in
a powdered form.
- Organic
mercury forms a compound with
carbon, most commonly methylmercury.
Organic mercury compounds are often
produced by microorganisms in the
soil or in water. Methylmercury
is often found in fish.
People
are regularly exposed to all three
types of mercury, although the organic
kind is the most likely to cause adverse
health
effects because of its tendency
to build up within the body.
Who
is at risk from mercury exposure?
Mercury
is toxic at high levels; it most often
affects the nervous system. Developing
fetuses appear to be the most vulnerable
to mercury
exposure, because their brains
and bodies are not yet fully developed.
Babies born prematurely, as well as
infants and young children in general,
have increased sensitivity to mercury
because their nervous systems are
still developing.
What
are the current limits set on mercury
exposure?
Safe
limits for mercury exposure are established
by various organizations, such as
the Environmental Protection Agency
(EPA), the Food and Drug Administration
(FDA), and the World Health Organization
(WHO). There is considerable variation
in their recommendations, largely
because of a difference in safety
margins. The EPA sets the lowest limit
at 0.1 mg/kg body weight per day.
Negative reaction is not certain to
occur above this level, but mercury
exposure below this level should not
lead to health problems.
What
are the symptoms of mercury exposure?
Symptoms
of mercury poisoning are progressive,
as attested to by the epidemics in
Japan and Iraq. The first stage is
known as paresthesia, and it is distinguished
by a tingling or numb sensation in
the fingers, toes, and face. Paresthesia
may be followed by:
- Difficulty
walking and speaking
- Impaired
vision and hearing
- Fatigue
and weakness
- Headache
and trouble concentrating
- Tremors
Mercury poisoning is most often signified
by nervous system disorders, such
as those mentioned above. Damage to
fetuses may also include digestive
and kidney problems, in addition to
mental and nervous system disorders.
Severe cases of mercury poisoning
may result in coma or death.
Are
there tests for mercury exposure?
Currently,
there are two tests available to determine
a person's level of mercury exposure.
A blood test can check for all three
types of mercury (metallic, inorganic,
and organic) but must be done within
a few days of exposure in order to
be accurate. Eating fish close to
the time of the test can influence
the results. A urine mercury test
can check for metallic and inorganic
mercury, but organic mercury is not
excreted from the body in urine. With
both tests, if the results are above
a specified level, they must be reported
to the U.S. Health Department.
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