News release of Thu 24-Apr-2008
from the University of Texas Health Science Center at San Antonio,
Research led by Raymond Palmer, Ph.D., of The University of Texas Health
Science Center at San Antonio is the first to show a statistical relationship
between autism prevalence and proximity to mercury-emitting sites.
How do mercury emissions affect pregnant mothers, the unborn and toddlers?
Do the level of emissions impact autism rates? Does it matter whether
a mercury-emitting source is 10 miles away from families versus 20 miles?
Is the risk of autism greater for children who live closer to the pollution source?
A newly published study of Texas school district data and industrial mercury-release
data, conducted by researchers at The University of Texas Health Science
Center at San Antonio, indeed shows a statistically significant link between
pounds of industrial release of mercury and increased autism rates. It
also shows - for the first time in scientific literature - a statistically
significant association between autism risk and distance from the mercury source.
“This is not a definitive study, but just one more that furthers
the association between environmental mercury and autism,” said
lead author Raymond F. Palmer, Ph.D., associate professor of family and
community medicine at the UT Health Science Center San Antonio. The article
is in the journal
Health & Place.
Dr. Palmer, Stephen Blanchard, Ph.D., of Our Lady of the Lake University
in San Antonio and Robert Wood of the UT Health Science Center found that
community autism prevalence is reduced by 1 percent to 2 percent with
each 10 miles of distance from the pollution source.
“This study was not designed to understand which individuals in the
population are at risk due to mercury exposure,” Dr. Palmer said.
“However, it does suggest generally that there is greater autism
risk closer to the polluting source.”
The study should encourage further investigations designed to determine
the multiple routes of mercury exposure. “The effects of persistent,
low-dose exposure to mercury pollution, in addition to fish consumption,
deserve attention,” Dr. Palmer said. “Ultimately, we will
want to know who in the general population is at greatest risk based on
genetic susceptibilities such as subtle deficits in the ability to detoxify
The new study findings are consistent with a host of other studies that
confirm higher amounts of mercury in plants, animals and humans the closer
they are to the pollution source. The price on children may be the highest.
“We suspect low-dose exposures to various environmental toxicants,
including mercury, that occur during critical windows of neural development
among genetically susceptible children may increase the risk for developmental
disorders such as autism,” the authors wrote.
• Mercury-release data examined were from 39 coal-fired power plants
and 56 industrial facilities in Texas.
• Autism rates examined were from 1,040 Texas school districts.
• For every 1,000 pounds of mercury released by all industrial sources
in Texas into the environment in 1998, there was a corresponding 2.6 percent
increase in autism rates in the Texas school districts in 2002.
• For every 1,000 pounds of mercury released by Texas power plants
in 1998, there was a corresponding 3.7 percent increase in autism rates
in Texas school districts in 2002.
• Autism prevalence diminished 1 percent to 2 percent for every 10
miles from the source.
• Mercury exposure through fish consumption is well documented, but
very little is known about exposure routes through air and ground water.
• There is evidence that children and other developing organisms are
more susceptible to neurobiological effects of mercury.
“We need to be concerned about global mercury emissions since a substantial
proportion of mercury releases are spread around the world by long-range
air and ocean currents,” Dr. Palmer said. “Steps for controlling
and eliminating mercury pollution on a worldwide basis may be advantageous.
This entails greener, non-mercury-polluting technologies.”
The U.S. Environmental Protection Agency (EPA) estimated environmental
mercury releases at 158 million tons annually nationwide in the late 1990s,
the time period studied by the Texas team. Most exposures were said to
come from coal-fired utility plants (33 percent of exposures), municipal/medical
waste incinerators (29 percent) and commercial/industrial boilers (18
percent). Cement plants also release mercury.
With the enactment of clean air legislation and other measures, mercury
deposition into the environment is decreasing slightly.
Dr. Palmer and his colleagues pointed out the study did not reflect the
true community prevalence rates of autism because children younger than
school age are not counted in the Texas Education Agency data system.
The 1:500 autism rates in the study are lower than the 1:150 autism rates
in recent reports of the U.S. Centers for Disease Control and Prevention.
Furthermore, the authors note that distance was not calculated from individual
homes to the pollution source but from central points in school districts
that varied widely in area.
Data for environmentally released mercury were from the United States Environmental
Protection Agency Toxics Release Inventory. Data for releases by coal-fired
power plants came from the same inventory and from the Texas Commission
for Environmental Quality. Data for school district autism came from the
Texas Education Agency.
Palmer, R.F., et al., Proximity to point sources of environmental mercury
release as a predictor of autism prevalence.
Health & Place (2008), doi:10.1016/j.healthplace.2008.02.001.