Mercury in Air Pollution: A Link to Autism?
More Autism Seen in Texas Counties With Most Mercury Pollution
March 18, 2005 - Can mercury in air pollution cause autism? Nobody knows.
But a new study suggests it's worth a look.
Mercury is one heck of a toxic substance. A fraction of a teaspoon can
render all the fish in a 20-acre lake unsafe to eat.
A recent Institute of Medicine study found no link between the tiny amounts
of mercury in But the jury is
still out on whether prenatal exposure to mercury might affect brain
Could environmental exposure to mercury affect autism rates? Raymond F.
Palmer, PhD, and colleagues at the University of Texas Health Science Center
explored the issue. They looked at EPA figures on industrial mercury release --
most of which comes from coal-fired power plants -- in 254 Texas counties. They
compared these figures to autism rates from the counties' 1,184 school
districts, taking into account other factors linked to autism.
Mercury Dumping, More Autism
"We found that for every 1,000 pounds of mercury released by industry,
there was a 17% increase in autism," Palmer tells WebMD. "This is one
of the most highly toxic [nerve-damaging substances] on earth. So when we talk
about 50 pounds, 1,000 pounds, 2,000 pounds released into the environment, this
is a tremendous amount of potential exposure. But we do not know how these
exposures get into the body."
The findings are scheduled to appear in the journal Health &
No Proof Mercury Pollution Causes Autism
Palmer is quick to point out that this kind of study does not prove mercury
pollution causes autism.
"We show a significant relationship between mercury release into the
environment and autism. But that does not prove causation," Palmer
Palmer's team is planning a long-term study to see whether actual fetal
mercury exposure can be linked to autism.
"The ultimate goal of this work is to help us think about what we want
to let out in the environment," Palmer says. "Is there an acceptable
risk for mercury exposure? We don't know. We would like to affect political
action, but we need harder data to do that. This study is just a first
Philip W. Davidson, PhD, is studying the effects of mercury exposure from
eating mercury-contaminated fish on child development. He's professor of
pediatrics and chief of the Strong Center for Developmental Disabilities at the
University of Rochester School of Medicine and Dentistry in New York.
"The question is, if a fetus is exposed to mercury, does that raise the
threshold for autism? Nobody knows," Davidson tells WebMD. "As far as I
know, no study has isolated symptoms of autism in individuals exposed to methyl
mercury [the most dangerous form of mercury]. … We think autism comes from
prenatal sources. Does mercury trigger autism? Who knows? We don't yet have any
Women, Fish, and Mercury
Davidson and colleagues are studying mercury exposure in pregnant women and
their offspring in Seychelles, where the diet contains large amounts of fish.
He warns, however, that the study of mercury is very complex. Studies must take
into account the form of mercury, the dose of mercury, and the time of life a
person is exposed to mercury.
So far, he says, the data suggest that fetal exposure to mercury is more
likely to be harmful than mercury exposure during childhood.
To protect developing babies from high levels of potentially brain-damaging
mercury, the government issued guidelines in March 2004 to who are pregnant, nursing, or even considering having children
to eat no more than two servings of fish each week.