A team of US researchers has shown that pregnant women exposed to certain chemical pollutants can double their risk of having children with autism. Diesel exhaust, dichloromethane, mercury, manganese and lead are among are the most likely culprits for the increase.
Around 1 in every 100 children is diagnosed with autism, but it is still a very poorly understood condition. Although there is some evidence for a genetic component, environmental factors are also undoubtedly important. Usually apparent before the child reaches 3 years old, autism is characterized by poor social interactions and communication, often accompanied by repetitive behavior. This condition affects how the brain processes information, in particular how nerve cells connect and communicate.
Analyzing the prevalence of autism, researchers observed a strong link between the risk of children developing this condition and mothers living in highly polluted areas at the time the child was born. Diesel particulates and mercury doubled the risk of having a child with autism, while dichloromethane, lead and manganese were associated with a 50% rise.
This means, for example, whereas the number of expected cases of autism in areas of low pollution is around 2 in 200, this figure may reach 3 or 4 in 200 in areas with high levels of chemical pollutants.
These are very strong results indentifying a link between incidence of autism and pollution with specific types of chemicals. This can be further confirmed by measuring directly the levels of such chemicals in blood samples from women living in contrasting areas in terms of pollution during their pregnancy.
In the past there have been many factors suggested to increase the risk of autism, including not only the well-known and controversial case of the MMR vaccines, but also alcohol and drug abuse during pregnancy, or exposure to pesticides, heavy metals or certain solvents. In most cases research is not reliable, and impact on autism incidence has not been proven.
In contrast, this is an important study adding to the increasing evidence that poor air quality during pregnancy can have detrimental effects on the baby, which may only be detected later in development. It’s therefore vital that policy makers consider this and other studies when deciding whether current allowed pollution levels should be reviewed and altered, if needed.
A L Roberts et al., Env Health Persp., 2013, DOI: 10.1289/ehp.1206187