Possible Mercury, Autism Connection Found in Study

Studying individual school districts in Texas, the epidemiologists found that those districts with the highest levels of mercury in the environment also had the highest rates of special education students and autism diagnoses.

The study does not prove that mercury causes autism, cautioned the lead author, Raymond F. Palmer of the University of Texas Health Science Center in San Antonio, but it provides a "provocative" clue that should be further investigated.

"Mercury is a known neurotoxin," said Dr. Isaac Pessah of UC Davis' MIND Institute, who was not involved in the study. "It's rather intriguing that the correlation is so positive," meaning that there was a strong, direct relationship between mercury and autism levels. "It makes one worry."

California has the highest environmental burden of mercury of any state in the country, and it also has what appears to be the highest rate of autism as well -- although some critics attribute this perceived high rate to enhanced surveillance associated with the state's special education program.

Autism is a severe developmental disorder in which children seem isolated from the world around them. There is a broad spectrum of symptoms, but the disorder is marked by poor language skills and an inability to handle social relations.

The incidence of autism has grown dramatically over the last two decades, from about one in every 2,000 children to as high as one in every 166. Researchers have been hard-pressed to explain the increase, but many believe mercury to be the culprit.

The purported link between autism and mercury has been a subject of intense debate. In the past it has centered primarily on the mercury-containing preservative thimerosal, which was once widely used in vaccines.

Many parents have argued that thimerosal causes autism because their children seemed to develop the neurological disorder shortly after they received childhood vaccinations.

That link has been largely discredited, and researchers are beginning to look at the potential effects of the metal from other sources.

Mercury is routinely released from power plants burning fossil fuels, and it spreads widely in air and water. Much of the fish consumed in some regions is contaminated with mercury. In California, gold mining was a big mercury source, and there are many mercury hot spots near mines and downstream, such as in Clear Lake.