Pollution could be a factor in autism, researchers have found.

They say children with autism spectrum disorder (ASD) were more likely to have been exposed to higher levels of certain air toxics during their mothers' pregnancies and the first two years of life compared.

The find could help explain the rise in cases.

The investigation of children in southwestern Pennsylvania will be presented today at the American Association for Aerosol Research annual meeting in Orlando.

'Autism spectrum disorders are a major public health problem, and their prevalence has increased dramatically,' said Evelyn Talbott of Pitt Public Health, who led the research.

'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.'

Dr. Talbott and her colleagues performed a population-based study of families with and without ASD living in six southwestern Pennsylvania counties.

The researchers found links between increased levels of chromium and styrene and childhood autism spectrum disorder, a condition that affects one in 68 children.

'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,' said Grant Oliphant, president of The Heinz Endowments.

'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.

'Addressing this issue must remain one of our region's top priorities.'

Autism spectrum disorders 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 does not fully explain the increased prevalence.

Both genetic and environmental factors are believed to be partially responsible.

'Our results add to the growing body of evidence linking environmental exposures, such as air pollution, to ASD,' said Dr. Talbott.

'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.'