Autism, mercury possibly linked

Texas researchers have found a possible link between autism and mercury in the air and water.

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

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

"Mercury is a known neurotoxin," said Dr. Isaac Pessah of the University of California, Davis' M.I.N.D. Institute, who was not involved in the study. "It's rather intriguing that the correlation is so positive. It makes one worry."

California has the highest environmental burden of mercury of any state and it has what appears to be the highest rate of autism, 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 in the past 20 years, 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 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 largely has been 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 the new study, Palmer and his colleagues used EPA data about the environmental release of mercury in 2001 in Texas' 254 counties and correlated that with the number of special-education cases and autism diagnoses in the nearly 1,200 school districts. Texas is fourth in the annual amount of mercury released into the environment, trailing California, Oregon and West Virginia.

The study, which will appear in the peer-reviewed journal Health & Place, found that every 1,000 pounds of mercury released into the environment produced a 43 percent increase in special-education services and a 61 percent increase in the autism rate.

The one exception to the rule was Brewster County, which had a high autism rate but did not report significant mercury levels to the EPA. When Palmer investigated, however, he found that the county had been home to one of the largest mercury mines in the nation.

Much more work will be required to determine whether mercury is actually the causative agent in the disorder.