Children exposed to certain types of air pollution during pregnancy and early in life are more likely to develop autism, according to a study of families living in Pennsylvania.
“Autism spectrum disorders are a major public health problem, and their prevalence has increased dramatically,” says Evelyn Talbott, professor of epidemiology at University of Pittsburgh Public Health.
“Despite its serious social impact, the causes of autism are poorly understood. Very few studies of autism have included environmental exposures while taking into account other personal and behavioral risk factors. Our analysis is an addition to the small but growing body of research that considers air toxics as one of the risk factors for ASD.”
Researchers performed a population-based study of families with and without ASD living in six southwestern Pennsylvania counties. Results show links between increased levels of chromium and styrene and childhood autism spectrum disorder, a condition that affects one in 68 children.
Talbot presented the preliminary findings at the American Association for Aerosol Research annual meeting.
Autism spectrum disorders (ASDs) are a range of conditions characterized by social deficits and communication difficulties that typically become apparent early in childhood. Reported cases of ASD have risen nearly eight-fold in the last two decades.
While previous studies have shown the increase to be partially due to changes in diagnostic practices and greater public awareness of autism, this doesn’t fully explain the increased prevalence. Both genetic and environmental factors are believed to be partially responsible.
Researchers interviewed 217 families of children with ASD and compared these findings with information from two separate sets of comparison families of children without ASD born during the same time period within the six-county area. The families lived in Allegheny, Armstrong, Beaver, Butler, Washington, and Westmoreland counties, and the children were born between 2005 and 2009.
One of the strengths of the study was that it had “two types of controls, which provided a comparison of representative air toxics in neighborhoods of those children with and without ASD,” Talbott says.
For each family, the team used the National Air Toxics Assessment (NATA) to estimate the exposure to 30 pollutants known to cause endocrine disruption or neurodevelopmental issues. NATA is the Environmental Protection Agency’s (EPA) ongoing comprehensive evaluation of air toxics in the US, most recently conducted in 2005.
Styrene and chromium
Based on the child’s exposure to concentrations of air toxics during the mother’s pregnancy and the first two years of life, the researchers note that children who fell into higher exposure groups to styrene and chromium were at a 1.4- to two-fold greater risk of ASD, after accounting for the age of the mother, maternal cigarette smoking, race, and education.
Other NATA compounds associated with increased risk included cyanide, methylene chloride, methanol, and arsenic. As these compounds often are found in combination with each other, further study is needed.
Styrene is used in the production of plastics and paints, but also is one of the products of combustion when burning gasoline in vehicles. Chromium is a heavy metal, and air pollution containing it typically is the result of industrial processes and the hardening of steel, but it also can come from power plants. Cyanide, methylene chloride, methanol, and arsenic are all used in a number of industries or can be found in vehicle exhaust.
“Our results add to the growing body of evidence linking environmental exposures, such as air pollution, to ASD,” Talbott says. “The next step will be confirming our findings with studies that measure the specific exposure to air pollutants at an individual level to verify these EPA-modeled estimates.”
Source: University of Pittsburgh