Los Angeles Times  [Printer-friendly version]
June 23, 2006


Bay Area children with the disorder are 50% likelier to be from areas
high in several toxic substances. Scientists say more research is

[Rachel's introduction: 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.]

By Marla Cone

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.

They found that the children with the autism disorders were 50% more
likely than the non-autistic children to be born in areas with higher
estimated levels of three metals and two chlorinated solvents:
mercury, cadmium, nickel, trichloroethylene and vinyl chloride. No
significant link was found with 14 other solvents and metals,
including compounds such as lead, benzene and chromium.

The national autism rate is six children per 1,000, so a 50% increase
would elevate that rate to nine per 1,000.

The biggest increase came with heavy metals including mercury, a
pollutant from power plants, factories and mines that can disrupt
brain development.

The Bay Area was chosen for the study because extensive data are
readily available there because of a federally funded program to count
and track autistic children. The region's toxic air pollution is
considered typical for urban areas.

San Francisco County had the highest estimated levels of metals and
solvents, including mercury, and Marin County had the lowest of those
studied. But the researchers did not compare autism prevalence by

In their report, published online Wednesday in the journal
Environmental Health Perspectives, the authors said their research
"suggests that living in areas with higher ambient levels of hazardous
air pollutants, particularly metals and chlorinated solvents, during
pregnancy or early childhood, may be associated with a moderately
increased risk of autism. These findings illuminate the need for
further scientific investigation, as they are biologically plausible
but preliminary and require confirmation."

The study is the first to look for a connection between autism among
children and levels of hazardous air pollutants at birth. Last year,
scientists who compared volumes of industrial mercury emissions in
Texas with autism in schoolchildren reported a similar link.

Autism is believed to start in the womb, early in pregnancy, when the
brain develops. Genetic factors determine who is susceptible, but
experts theorize that environmental factors contribute.

The new study found that mercury was the "most significant correlation
with autism," Pessah said, "but every family may not be affected the
same way because of their genetic makeup."

Many parents of autistic children blame vaccines that contained a type
of mercury called thimerosal. Expert reviews have found no link
between vaccines and autism, but some scientists do not consider them

No assumptions about vaccines can be made on the basis of the air
pollution study. "Mercury in the air is a different type than in
vaccines," Windham said.

The new study examined elemental mercury, which is released into the
air from coal-burning power plants, chlorine factories and gold mines.
It spreads globally and builds up in food chains, particularly in
oceans. Levels of mercury are increasing in many parts of the world,
largely from power plants in China and India.

The researchers had not expected to be able to discern a relationship
between autism and the air pollution data.

The five metals and solvents are common industrial pollutants, but air
is only one source of exposure, because they also contaminate water
and food.

Some experts say that if there is a link between mercury and autism,
it most likely comes from fish consumption, the main route of mercury
exposure. A 20-year, ongoing study in Denmark's Faroe Islands has
shown that children have slightly reduced intelligence when mothers
consumed excessive mercury in seafood.

The largest limitation or uncertainty in the Bay Area study is that
the pollution data did not come from measurements of compounds to
which the mothers were actually exposed. Instead, they were based on
estimates calculated by the U.S. Environmental Protection Agency using
computer modeling of industrial emissions.

Windham said that "there could be other explanations" for the link
they found. For example, it could be that women who live in the worst-
polluted areas also smoke more or eat more contaminated seafood. The
scientists did not track down the mothers to compare lifestyles.

Researchers at Johns Hopkins University's School of Public Health are
conducting a similar study in the Baltimore area to see if they
replicate the findings.