Researchers have found
evidence that high levels of mercury exposure while a child
is still in the womb can cause lasting, irreversible brain damage.
Mercury in the children's
diets also seemed to cause damage, which the researchers say
might suggest a revision of current fish consumption guidelines
is in order.
Other experts, however,
do not believe this is the final word. "I don't think it's definitive,"
says Dr. Gary Myers, a professor of neurology and pediatrics
at the University of Rochester Medical Center.
This paper and another,
which reports heart function changes related to mercury, appear
in the February issue of the Journal of Pediatrics.
In high enough quantities,
methylmercury, which can contaminate both salt water and freshwater
fish, is known to have adverse effects on the nervous system.
National and state
guidelines on fish consumption differ but focus on protecting
pregnant women and women of childbearing age. Some advisories
also extend to children.
The current researchers
looked at brain function in 14-year-old children in the Faroe
Islands, located in the North Atlantic Ocean between Norway
and Iceland. The diet in the Faroes is high in mercury-containing
fish, especially whale meat.
"In the Faroes,
when the mothers were pregnant, the exposure was about five
to 10 times higher than the U.S. average exposure, but it has
declined substantially," says study author Dr. Philippe Grandjean,
an adjunct professor of environmental health at Harvard School
of Public Health in Boston.
The children had
been exposed to mercury both prenatally and after they were
More than 1,000
mothers and their children participated in the study, providing
cord blood samples taken at birth and hair samples from their
children, taken at ages 7 and 14.
In most cases, the
mercury level in the mothers' hair at the time of birth exceeded
one microgram per gram, which is the exposure limit recommended
by the U.S. Environmental Protection Agency. Children had lower
measured brain function by putting electrodes on the children's
skull (much like an EKG), and stimulating the brain with different
sounds. One ear got a sharper "rat-a-tat-tat" sound, while the
other got a dull hissing, Grandjean explains.
The electronic system
connected to the electrodes was capable of picking up tiny signals
from inside the brain.
"It's a simple method
of looking into how the nerve cells fire information to each
other using electrical signals," Grandjean says. "That's where
we saw that there were delays the higher the mercury exposure."
saw the same effects in the children when they were 7 and 14.
"This indicates to us that if a brain is exposed to mercury
during development in the mother's womb, then the effect that
we see during childhood is going to be a lasting effect," he
says. "We're seeing that a brain that is affected during development
will not recover, and I think this sort of puts the mercury
question into perspective. If this was just a passing effect,
it's something entirely different. But here we're talking about
something that will stay with that child for a lifetime, and
that will affect the child's education, academic success, financial
success and whole equality of life."
delays are associated with deficits in memory, language, attention,
and motor speed, among other things, Grandjean says.
also found that current dietary levels of mercury were also
having an effect on the children. "We're now talking about effects
that actually occur within the range of exposure in the United
States," Grandjean says. "It indicates to me that the vulnerability
of the brain during development is not just a matter of gestation.
This is something that extends into childhood and probably into
Other experts are
not convinced that current levels of mercury pose such grave
"Exposure to mercury
in the Faroes is associated with consumption of whale meat,
and whales are not part of most people's seafood diet, and they
happen to have a variety of other toxins present in them," says
Myers, the University of Rochester neurologist. "It's very hard
to extrapolate from a diet that contains sea mammals to one
that's a pure fish diet. Some people feel that that's legitimate,
but it seems a bit of a stretch to myself."
In addition, Myers
adds, some of the children studied did eat whale meat after
they were born.
"The next logical
step would be to do the same thing with people who only consume
fish," Myers says. "The exposure here in the United States is
from fish, so if you want to know what happens to people who
eat fish, the logical way to approach that is to look at them."
Reference Source 101