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Mercury
Mercury is a metal that occurs in three forms: elemental, inorganic salts, and
organic forms. All are toxic, but methylmercury, one of the organic forms, is of
particular concern because it bioaccumulates in fish and is 100% absorbed after
ingesting contaminated fish. For most people,
this is the primary source of exposure.
Why is mercury pollution bad?
Mercury can cause learning disabilities, developmental delays, and problems with
fine motor coordination in children. Like lead, mercury is a known neurotoxin
that is particularly dangerous to fetuses, infants, and young children because
their brains are still developing. Levels that produce no symptoms in a mother
can lead to permanent and occasionally devastating neurologic deficits in a
child (Davidson, et al., 2004).
Based on recent government and other studies, up to 8% of
pregnant women may have levels above the USEPA guideline of a maximum of 11 ppm
(Cernichiari, et al., 1995;
Pilgrim, et al., 2000). This
translates to more than 300,000 babies exposed to possibly neurotoxic levels of
mercury in utero. Although these levels do not result in the severe mental and
motor problems seen in infants born to women who ate heavily contaminated fish,
such levels have been associated with subtle but measurable neurologic deficits
including problems with attention, memory, learning and language.
The following is a summary of several major studies on mercury
and health.
- In the 1950s and ‘60s in Minamata Bay and
Niigata, Japan, industrial releases of mercury compounds
into the bay led to highly contaminated fish, which were eaten
unknowingly by people living in the region (Kondo,
2000). At least 2,000 individuals were officially recognized
as poisoned. The severest brain damage occurred in
children who had been exposed during pregnancy (Davidson,
et al., 2004;
Harada, et al., 1978).
- Methylmercury poisoning also occurred in Iraq
in 1971-72 as a result of families eating bread made from
seed grain coated with a mercury-containing fungicide. Some
6,530 patients were admitted to the hospital and nearly 500
died. These data suggested that developmental delays
could be associated with maternal mercury hair levels as low as
7-10 ppm (Amin-zaki,
et al., 1978;
Myers, et al., 2000).
- Investigators are following more than 700
mother-child pairs of primarily African and/or Asian ethnicity
in the Republic of Seychelles off the coast of Africa (Myers,
et al., 2003). This study has followed many children for
over 10 years, with only one cognitive test showing impairment.
Maternal hair levels were 0.5 to 26.7 ppm.
- A study in the Faroe Islands is tracking
approximately 900 children born in 1986-87 (Grandjean,
et al., 1997). Results indicate associations between
prenatal mercury exposure (maternal hair levels = 2.6 to 16.3
ppm) and tests of memory, attention, language, and
visual spatial perception measured at 7 years of age, as
well as an association between prenatal mercury exposure and
heart rate and blood pressure (Sorenson,
et al., 1999).
- Numerous other smaller or cross-sectional
studies have been conducted in New Zealand, Canada, Brazil,
Sweden, Brazil and elsewhere.
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