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Data correlate mercury, autism

March 18, 2005

Cindy Tumiel
Express-News Staff Writer
San Antonio Express-News

Autism rates are higher in Texas counties with high levels of reported mercury emissions, San Antonio researchers found, adding another bit of fuel to the debate over whether the toxic substance is related to the increasing number of autistic children.

Mercury, a neurotoxin, is one of the pollutants discharged from power plants that burn fossil fuels. It spreads through air and water and is blamed for widespread fish contamination in some areas. It now is being fingered as one of the reasons behind the rapid rise in the number of autistic children over the past two decades.

Raymond Palmer and colleagues at the University of Texas Health Science Center compared 2001 mercury emissions to the number of autistic children enrolled in the state's 1,200 school districts. The data came from the Environmental Protection Agency and the Texas Education Agency.

Counties with high rates of mercury emissions had an average 17 percent increase in the rate of autism for every 1,000 pounds discharged, said Palmer, an associate professor of family and community medicine.

He cautioned that the study doesn't prove mercury causes autism, but it does point to a need for more research.

"It's a crude study that looks at rates of autism and pounds of emissions," Palmer said. "A correlation doesn't mean cause."

Autism is a severe developmental disorder in which children withdraw from their surroundings. Autistic children also have poor language skills and an inability to handle personal relationships.

There's been a tenfold increase in the number of cases in the past 20 years. An estimated one in every 166 children is diagnosed with the disorder.

Scientists are investigating genetic and environmental causes. The debate over mercury initially centered on thimerosal, a mercury-containing preservative once used in vaccines. That theory is largely discredited, but scientists are looking at other sources of the neurotoxin.

Palmer's study has been published online and is to appear in a future issue of the scientific journal Health & Place.

"Overall this lends itself to support the hypothesis out there that autism is related to mercury," Palmer said. "We hear about it in aerosol and we hear about it in fish. This study takes another angle; there are other sources of exposure to mercury, too," he said.

"These types of studies are useful in the early stages of a field," said Dr. Irva Hertz-Picciotto, a professor at the University of California Davis. "They are never definitive, but they point you in the direction of things you should look at."

But she cautioned that researchers didn't look at other industrial pollutants from plants in the region that could be causing problems.

"To focus on one thing at the exclusion of all others can be confounding," Hertz-Picciotto said.

The findings are fodder for Texas environmental groups pushing for legislation limiting power plant emissions, said Karen Hadden, executive director of the Texas SEED Coalition.

"What's most important overall is the human impact," Hadden said. "We can't afford continued loss of IQ in our children."

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