Autism risk higher near toxic waste sites.

Apr 13, 2009

DeSoto, MC. 2009. Ockman's Razor and Autism: The case for developmental neurotoxins contributing to a disease of neurodevelopment.  Neurotoxicology doi:10.1016/j.neuro.2009.03.003

Children living near Superfund sites are more likely to be autistic.

Autism rates among school children living within a 10- or 20-mile radius of toxic waste sites are nearly twice as likely to have autism compared to children living farther away from such sites. These data support the widely speculated but controversial idea that exposure to chemical contaminants can increase the risk of developing autism.

The incidence of autism in the US has risen dramatically during the past 20 years. Improved diagnoses may contribute to the elevated number of cases, but a recent study calculates that better diagnosis does not explain a large part of the rise. Environment, such as exposure to chemicals, is thought to be a primary driver of the increase.

The researchers investigated autism rates in children attending public schools located near Superfund sites in Minnesota. Superfund sites are toxic waste sites designated by the US Environmental Protection Agency (EPA) as hazardous for human health. Among the pollutants frequently found at the sites are chloroethelyenes, benzene and metals (lead, mercury, cadmium, chormium, arsenic).

The study compared autism rates among public school children in 46 school districts located within 10 miles of one or more Superfund sites to rates among children within 288 school districts that did not have a site within 10 miles.

Rates of the disorder were one and a half times higher in the districts within 10 miles of the toxic sites. That translates into 1 child in 92 in districts closer to the sites compared to 1 child in 132 in the districts farther away. Schools within a 20-mile radius of Superfund sites had similar autism trends as the schools with 10 miles of the sites. 

Autism encompasses a spectrum of disorders relating to impaired social behavior, including delayed speech, avoiding eye contact and repetitive behavior. The disease is more common in boys than girls and emerges in early childhood.

Autism is believed to result from improper brain organization during gestation. Where the mothers of the children in this correlational study lived while they were pregnant was not taken into account and is thus a notable and important limitation. 

Correlational studies look for associations between disease and potential environmental factors.  It is important to keep in mind that correlational studies like this one are often the first to identify potential links between an environmental exposure and a disease but that other information is needed to verify the association.  For example, human exposure around Superfund sites is generally minimal, so it is unclear how the children would have been exposed to contaminants. In addition, the children in this study were not tested for contaminants in the blood or urine to confirm that they were indeed exposed.

According to the authors, rates in Minnesota are eight times higher now than they were in the 1980s. They are particularly high among Somali immigrants, for reasons that remain unclear. The authors did not state if any of the children in their study were from Somalia.