Children with autism disorders in the San Francisco Bay Area were 50% more likely to be born in neighborhoods with high amounts of several toxic air contaminants, particularly mercury, according to a first-of-its-kind study by the California Department of Health Services.
The new findings, which surprised the researchers, suggest that a mother's exposure to industrial air pollutants while pregnant might increase her child's risk of autism, a neurological condition increasingly diagnosed in the last 10 years.
But the scientists cautioned that the link they found in the Bay Area is uncertain and that more definitive evidence would be needed before concluding that mercury or any other pollutant could trigger autism.
Gayle Windham, the study's lead researcher and senior epidemiologist in the department's environmental health investigations branch, called it "a single small study" and "a first look" at whether toxic pollutants play a role in the neurological disorder, which is often marked by poor verbal and communication skills and withdrawal from social interaction.
Scientists have long wondered if the surge in diagnoses is due, in part, to environmental causes. Some of the increase comes from growing doctor and parent awareness, but experts say that cannot explain all of it.
"Clearly this suggests that there may be correlations between autism onset and environmental exposures, especially as it relates to metal exposures," said Isaac Pessah, a toxicologist who heads UC Davis' Center for Children's Environmental Health and Disease Prevention. Pessah, who was not involved in the study, is also a researcher at the university's MIND (Medical Investigation of Neurodevelopmental Disorders) Institute, which studies autism.
"It would be prudent to reserve judgment until we see if this study can be replicated and whether it's of general significance" by looking for the same link outside the Bay Area, he said.
About 300,000 U.S. children have been diagnosed with autism and often need special education. The study compared 284 children from six Bay Area counties who were diagnosed as having so-called autism spectrum disorders -- which include a less-severe syndrome called Asperger's -- with 657 children from the same counties without the disorders. All were born in 1994.
The scientists reviewed data for 19 hazardous air pollutants that are known or suspected neurotoxins: chemicals that have a toxic effect on the brain.
