New research provides further evidence for the previously suggested link between environmental exposures and autism. In the study, researchers found that children with autism were more likely to be exposed to specific air pollutants in the first 2 years of life and during their mother’s pregnancy than those without the disorder.
The research team, led by Dr. Evelyn Talbott, professor of epidemiology of the University of Pittsburgh Graduate School of Public Health, PA, recently presented their findings at the American Association for Aerosol Research annual meeting in Orlando, FL.
The prevalence of autism spectrum disorder (ASD) is on the rise in the US. In 2000, 1 in 150 children had the disorder, while current rates stand at 1 in 68. Although more and more children are being diagnosed with autism, the exact causes of the condition are unclear.
Some studies, however, have indicated that early exposure to environmental factors may contribute to its development. Earlier this year, for example, a study found that mothers exposed to pesticides during pregnancy are more likely to have children with autism.
This latest study, Dr. Talbott says, “is an addition to the small but growing body of research that considers air toxics as one of the risk factors for ASD.”
Children exposed to styrene and chromium ‘up to twice as likely to develop autism’
To reach their findings, the research team interviewed 217 families of children with autism. The children were born between 2005 and 2009, and the families resided in six counties in Pennsylvania: Allegheny, Armstrong, Beaver, Butler, Washington and Westmoreland.
The researchers estimated each family’s exposure to 30 air pollutants known to cause neurodevelopment problems or endocrine disruption, using the National Air Toxics Assessment, an ongoing assessment of air toxics in the US conducted by the Environmental Protection Agency.
For comparison, the team also interviewed and estimated the air pollutant exposure of two sets of families of children without autism who resided in the same areas. The children were also born during the same period.
Dr. Talbott says having two control groups is a strength of this study, as it “provided a comparison of representative air toxics in neighborhoods of those children with and without ASD.”
Results of the study revealed that children who were highly exposed to two specific air pollutants – styrene and chromium – during their mother’s pregnancy or up to the age of 2 years were up to twice as likely to have autism, compared with children who were not exposed to these pollutants.
Styrene is a compound often used in plastics and paints, and it is also produced by burning gasoline. Chromium is a heavy metal produced by steel hardening and other industrial processes, as well as power plants. Other air pollutants – including cyanide, methylene chloride, methanol and arsenic – were also linked to increased autism risk in children.
The team’s findings remained after accounting for mothers’ age, race, education and smoking during pregnancy. “Very few studies of autism have included environmental exposures while taking into account other personal and behavioral risk factors,” notes Dr. Talbott.
She says that these results “add to the growing body of evidence linking environmental exposures, such as air pollution, to ASD.”
“This study brings us a step closer toward understanding why autism affects so many families in the Pittsburgh region and nationwide, and reinforces in sobering detail that air quality matters,” says Grant Oliphant, president of The Heinz Endowments, a Pennsylvania-based organization that funded the research.
“Our aspirations for truly becoming the most livable city cannot be realized if our children’s health is threatened by dangerous levels of air toxics,” adds Oliphant. “Addressing this issue must remain one of our region’s top priorities.”
Pollution and brain development
These new findings are in line with other recent research indicating that developing brains are especially vulnerable to the effects of harmful chemicals. For instance, a study published just last month found that children living in urban areas are at increased risk for brain inflammation and other neurodegenerative changes, including Alzheimer’s and Parkinson’s disease. The results showed that when air particulate matter and their components such as metals are inhaled or swallowed, they pass through damaged barriers — including respiratory, gastrointestinal and the blood-brain barriers — and can lead to long-lasting harmful effects
Air pollution is known to affect small and large blood vessels throughout the body, leading to an increased risk of cardiovascular conditions like stroke and heart attack. By permanently affecting vascular structures in the brain, air pollution can also have serious effects on neural functioning and neural matter.
In past studies assessing exposure to pollutants in animals, researchers have found that air pollution causes damage to the central nervous system by altering the blood–brain barrier, causing neurons in the cerebral cortex to degenerate, destroying glial cells found in white matter, and by causing neurofibrillary tangles. These changes can permanently alter brain structure and chemistry, resulting in various impairments and disorders. Sometimes, the effects of neural remodeling do not manifest themselves for a prolonged period of time, while others can be seen as early as childhood.