With autism affecting one in 68 children and no conclusive answers about the causes of the disorder, many researchers are studying the possibility that environmental factors are influencing ASD. A number of important studies have indicated that there may be a link between the particulates and chemicals in air pollution and the likelihood that a child will develop autism.
Evidence Linking Autism to Air Pollution
Although there is a strong genetic basis for autism, researchers are studying the environmental factors like air pollution as well. In general, these studies focus on air pollution chemical and particulate exposure while in utero and soon after birth. Evidence seems to suggest that air pollution exposure during this important developmental window may worsen genetic vulnerabilities in some children.
Autism Rates Increase Near Freeways
One of the first studies to link autism and air pollution was conducted in 2010 and published in the journal Environmental Health Perspectives. The study examined more than 500 children, more than half of whom were diagnosed with autism. It compared the child's diagnosis with whether his or her mother lived near a freeway during her pregnancy.
Although the study did not focus on air particulates or chemicals in air pollution, it did find that the closer a mother lived to a freeway, the greater the chance that her child would develop autism.
Mercury Air Pollution
In 2011, the journal Reviews on Environmental Health published a study focusing on the rates of autism and Alzheimer's disease in areas with high levels of mercury air pollution in Texas and California. These areas were near coal-fired power plants and other sources of mercury air pollution, and the study found that there were also more cases of autism in these locations.
Although the study did not indicate a causal relationship, the authors stressed that it indicated a potential link.
Nitrogen Dioxide and Particulate Exposure
A 2013 study in the Journal of the American Medical Association also examined more than 500 children, about half of whom had ASD. The study found that exposure to nitrogen dioxide and particulate matter in the air during prenatal development and the first year of life significantly increased the likelihood of a child being diagnosed with autism.
The study authors cautioned that this showed a correlation between air pollution and autism and that a causal relationship had yet to be discovered.
Air Pollution Toxins
In 2014, another study, also published in Environmental Health Perspectives, examined several of the specific toxins in air pollution and how they relate to autism rates. The study focused on 325 cases of ASD and more than 22,000 neurotypical children and studied chemical exposure during pregnancy and early infancy.
The researchers found that exposure to diesel and mercury had the most significant link to autism diagnosis, but other chemicals, such as manganese, lead, and methylene chloride, were also implicated in an increased likelihood of developing the disorder. Further, the study found that these chemicals seemed to have a greater impact on baby boys than on baby girls.
Prenatal Particulate Matter Exposure
A 2014 study published in the journal Environmental Health Perspectives examined more than 1700 children, 245 of whom were diagnosed with ASD. The researchers measured the particulate matter in the air at the location where the children's mothers lived during pregnancy and found that higher levels of particulate matter increased the risk for autism.
Additionally, the risk seemed greatest when the mothers were exposed to the particulate matter during the third trimester of pregnancy.
A 2014 study in the journal Epidemiology built upon previous research by focusing on how air pollution might influence the expression of a gene that has also been previously linked with autism. Previous mouse studies had shown that the MET receptor tyrosine kinase gene became activated when exposed to chemicals mimicking air pollution, and this gene activation led to ASD symptoms.
Researchers studied more than 300 children to compare the level of air pollution exposure and whether this gene was turned on. The study found that exposure to air pollution, including nitrogen dioxide, particulate matter and ozone, was linked with this genetic vulnerability.
Does Air Pollution Cause Autism?
While these studies show a link between ASD and the chemicals and particulates in the air, they don't necessarily indicate that air pollution causes autism. Instead, they simply show that the level of air pollution seems to be a related factor. It is likely that others factors are involved. For instance, it may be that air pollution is higher in metropolitan areas, and these areas also have better resources for identifying autism.
In order to know whether these chemicals and particulates actually cause the disorder, scientists will need to do more research. It may be some time before the information they obtain can help prevent future cases of ASD, and researchers may discover a different cause for the disorder.
Implications for Families
There is a lot of research about factors that may influence autism, and it can be difficult to determine how the research actually impacts daily life for families.
Implications for Older Kids
The studies about autism and air pollution have focused on the prenatal period and early infancy. As of yet, there are no studies indicating a link between air pollution and autism in older kids and adults.
If you have an older child or are an adult with ASD, there may be no practical implications from this research. It's still a good idea to avoid air pollution as much as possible for other health reasons.
Implications for Infants and Pregnant Women
If you are pregnant or are the parent of a newborn, it may make sense to limit your air pollution exposure as much as possible. Air pollution isn't good for anyone, and if it is a possible factor in developing autism, it's wise to control it as much as is practical. Try some of these tips:
More Research Required
Although researchers have found a likely link between autism and air pollution, there is still a lot that isn't known. It will take time for scientists to determine whether particulates and chemicals in the air actually cause the disorder and how this information affects new and expectant parents. This is a promising area of research, and it's likely there will be many more studies on this topic.