Air Pollution May Play Role in Autism

Autism was more prevalent among children in areas of high pollution

(RxWiki News) Past research has posed many theories about factors that could influence autism in children, and the authors of a new study may have found one more. Children born in areas of high pollution may be more likely to have the disorder, the new study suggests.

The researchers found pollutants that may increase the risk for autism spectrum disorder (ASD) in children exposed to them and children of mothers who are exposed to them during pregnancy.

This finding may add to past research on the topic that suggested that environmental factors could be involved in the disorder.

ASD refers to a group of developmental disorders. It is often diagnosed before a child is 3 years old as symptoms become noticeable. The disorder is marked by social, communication and behavior problems.

Evelyn O. Talbott, DrPH, of the University of Pittsburgh, led the study.

The study authors found that children exposed to high levels of styrene, chromium, cyanide, methylene chloride, methanol and arsenol were more likely to be diagnosed with ASD. These chemicals are used to produce things like carpet or gasoline. Sometimes, the chemicals are cast into the air when they are used in places like factories — and they are thought to be harmful for people to breathe.

The children in the study were born between 2005 and 2009 in six counties in southwest Pennsylvania. The study authors studied families of 217 children with ASD. They also looked at the birth records of two separate sets of families with children — a total of more than 5,000 — without ASD.

To estimate the exposure each child had to toxins, the study authors used a tool developed by the Environmental Protection Agency (EPA). The tool is called the National Air Toxics Assessment (NATA). It is an ongoing assessment of air toxin concentrations and their health effects.

Those children most exposed to styrene and chromium had a 1.4 to 2 times greater risk for ASD than kids who were not exposed, the study authors found. Children exposed to cyanide also had a raised risk for ASD.

The authors took into account the age of the mother, maternal cigarette smoking, race and education — all factors that have been thought to increase a child's risk for autism.

Styrene is used to produce paint and plastics and is often found in car exhaust. Chromium is also found in car exhaust. Cyanide is sometimes released into the air during the production of fibers and plastic. Many of these pollutants are often found together, the study authors wrote.

These findings do not prove a direct causal relationship between toxins and ASD, said Glen R. Elliott, MD, PhD, an autism expert and professor at the University of California, San Francisco, in an interview with dailyRx News. Many factors could cause the disorder.

“Lots of investigators have found correlations between two measurements but it is much, much harder to establish that one causes the other,” Dr. Elliott said. “Furthermore, they looked at a quite narrow population. If their hypothesis is correct, one should see marked variability across the country based on rates of air pollution. To my knowledge, no such variation has been described."

Dr. Elliott said that comparing pollutant levels in other areas of the country to see whether the link with ASD remains could help researchers further understand this topic.

"Still, leads such as this ultimately may help us sort through environmental factors that may be a part of the overall cause of autism,” he said.

In 2004, 1 child out of 125 was diagnosed with autism. That figure is 1 in 68 today, reports the Centers for Disease Control and Prevention.

"Our results add to the growing body of evidence linking environmental exposures, such as air pollution, to ASD," Dr. Talbott said in a press release. She said the next step will be confirming the findings with studies that measure individual patients' exposure to air pollutants.

This abstract was presented Oct. 22 at the American Association for Aerosol Research annual meeting in Orlando, FL. Research presented at conferences has not necessarily been peer-reviewed.

The Heinz Endowments funded the study. The authors disclosed no conflicts of interest.

Review Date: 
October 23, 2014