Can air pollution cause autism?

In this article, we will discuss whether there is any link between air pollution and the rise in autism in children and fetuses. Next, we will try to see which pollutants are more dangerous, and lastly, we shall identify methods to deal with it.

Can air pollution cause autism?

Studies suggest that autism can be linked to exposure of pregnant mothers to air pollution. 

Autism spectrum disorder, or simply autism, refers to the affliction of neurodevelopmental conditions, which are characterized by varying degrees of difficulty in social interaction, difficulties in verbal and nonverbal communication, and repetitive behaviors. 

The specific trigger of autism cannot be identified, but it can be attributed to numerous factors, which can be based on the combination of genetic and nongenetic, or environmental influences. 

Over the past few years, a trend of increase has been seen in the number of reported cases of autism, especially in big cities, which have also shown an increase in the ambient air pollution levels.

What does research say?

Some studies have attempted to find an association between autism and air pollution. It was found that air pollution increases the relative risk of development of autism. 

However, it is not an absolute risk, since many other factors can also contribute towards development of autism.

We shall further discuss two case studies, with one held in a less polluted area, while the other is conducted in a highly polluted area.

Study in Vancouver metropolitan area, Canada, by Pagalan et al., 2019

A study was performed in the Vancouver metropolitan area, in which children born between 2004-2009 were studied. 

Out of the total 132256 children born, 1307 of them (nearly 1%) reported autism, with the number of male children testing positive for autism being five times higher than that for female children. 

Notably, in the same time period, the pollution levels for certain common air pollutants had fallen, from an annual mean of 5.7 to 5.0 μg/m3 in the case of PM2.5, 16.0 to 11.0 ppb in the case of NO, and 16.0 to 13.5 ppb in the case of NO2

According to the pollution index, these concentrations would classify the area as “less polluted”.

However, it was found out that the risk of autism had increased with exposure to air pollution, with nitrogen oxide (NO) showing a significant correlation.

Study in Los Angeles County, USA, by Becerra et al., 2013

Los Angeles is a metropolitan city, which holds importance in various aspects to the country. The city, owing to its traffic and industrialisation, is highly polluted. 

In fact, the term “LA smog”, used to describe smog formed due to interaction of light with constituents of vehicular emissions, was first observed in this city, hence the name.

In this study, children born between 1995-2006 to mothers residing in LA county were used as reference. Exposure to common pollutants released from vehicular exhausts were studied to identify a correlation between autism and air pollution.

The study reported that exposure of mothers during the period of their pregnancy to air pollution, particularly to ozone (O3) and particulate matter less than 2.5 microns (PM2.5) showed a significant correlation to increase in the odds for the child to be diagnosed with autism. 

However, the study failed to identify any association with other common air pollutants, such as polycyclic aromatic hydrocarbons (PAHs), certain species of PM2.5, and so on.

Study by Weisskopf et al., 2015

The aim of this study was to establish whether air pollution plays any role in development of autism in children and developing fetuses, or is it purely coincidental.

This study refers to the various studies conducted in different regions of the world. Out of these studies, two made a strong argument against the confounding nature of the problem.

It was found out that the child is at risk of developing autism during the entire course of pregnancy, as well as during the first three years of their life. 

However, the study suggests that the third trimester of pregnancy is the stage at which exposure to air pollution can have an increased chance of development of autism in the child.

Common pollutants linked to autism and their sources

Based on the studies mentioned above, the main pollutant species that play a critical role in development of autism in children are:

  • Nitrogen oxides (NOx), particularly NO2
  • Ozone (O3)
  • Particulate matter (PM10 and PM2.5)
  • Cigarette smoke

Nitrogen oxides (NOx)

 NOx species refers to various compounds that contain nitrogen and oxygen atoms in varying numbers. These are a pollutant of concern, as they increase the risk of respiratory infection. 

NOx are primarily traffic-related pollutants, since they are emitted from vehicular exhausts. Various studies have shown that NOx species, particularly NO2, can be linked to development of autism within children. 

These studies found out that for areas where traffic congestion was high, or an industrial area was nearby, the number of reported cases of autism within children was relatively higher.

NOx species can easily penetrate all the way to the lungs, from which they can enter the bloodstream and reach the fetus, where it can hamper the development of the brain. 

It can also affect infants and young children, as they have a higher breathing rate, therefore become more susceptible to the effects of NOx species on the development of cognitive skills.

Ground level Ozone (O3)

Ozone is a gas that is formed by interaction of light with oxygen molecules. It is a vital gas in the upper atmosphere, where it blocks the harmful UV rays from entering the atmosphere.

 However, when present at the ground level, it has negative implications on human health. 

Ozone is an unstable molecule. Upon breaking down, it can give rise to an oxygen atom, which is highly reactive in nature, and can attack the DNA and impair certain functions. 

These damages on a fetus or on a young child are much more pronounced, since they are developing.

Various studies have shown that ozone can have adverse effects that include functional,morphologic, immunologic, and biochemical alterations. 

Studies in the US and Europe have also shown a positive correlation between ground level ozone concentration and reported cases of autism in children.

Particulate Matter (PM)

PM refers to particles, either solid or liquid, that are mixed and suspended in the air. They are a major part of air pollutants, and have a variety of natural and anthropogenic sources. They usually range between 2.5 to 10 microns (PM10 and PM2.5).

Particulate matter is a major contributor to both long term and short term illnesses. There are many well-documented studies that have shown progression of illnesses with an increase in the concentration of PM. 

PM2.5 is of a major concern, as it can easily enter the lower respiratory tract, and is respirable. Moreover, PM is also linked to development of autism in fetuses, suggesting that they are capable of entering the mother’s bloodstream and entering the fetus’ body.

They can also act as adsorbents, allowing various elements to be stuck to their surface, which in turn can prove more harmful when inhaled, as they can include substances such as heavy metals, which can act as mutagens.

Cigarette smoke

Cigarette smoke is very toxic in nature. Apart from the pollutants mentioned above, it contains mutagens, carcinogens, and other substances that can have serious implications on the brain development of children.

Various studies have shown that exposure during the developmental phase, particularly of children and fetuses, to nicotine, the active ingredient in a cigarette, can significantly affect the development of the brain. 

Moreover, studies have also shown an association of onset of autism in fetuses of mothers who smoked while they were pregnant, or were exposed to secondhand smoke due to the environment.

FAQs: Can air pollution cause autism

How can air pollution affect my child?


Air pollution impacts neurodevelopment and cognitive ability, thereby triggering autism, other than the fact that it can trigger asthma, and childhood cancer. 

Not only that, children who have been exposed to high levels of air pollution may be at greater risk for chronic diseases such as cardiovascular disease later in life.

How to protect pregnant mothers and children from air pollution?

You can protect pregnant mothers and children from air pollution. It is evident that exposure to air pollution increases the likelihood of children to develop autism. 

Since autism has no cure as of now, prevention is better than cure. We can keep pregnant mothers and young children safe from autism in the following ways.

Avoid polluted places and places prone to pollution

It would be wise to refrain from going to polluted places such as areas which are prone to traffic congestion, industrial areas, and so on. 

Use a face mask when going to polluted areas

There would be circumstances where it is impossible to go to an area which is polluted. In such cases, it would be wise to wear a face mask, particularly N95 masks, as they are efficient in blocking out particulate matter and certain gaseous pollutants that would have adverse effects on your health.

Keep your indoor air clean

An average American spends 93% of their total life indoors. 87% of their life is inside buildings, then another 6% of their life is in automobiles. 

Over the last several years, a significant amount of scientific reports provide evidence of air pollution inside buildings and homes, referred to as indoor air pollution (IAP), which is more serious than outdoor air pollution, even in industrialised cities and metropolitan areas. 

Thus, a person has a higher health risk from indoor air pollution than from outdoor air pollution. The best way to deal with IAP is by the following methods:

Improving ventilation of the house, which would help to dilute the indoor air pollution level by introducing outdoor air, and carry the pollutants out of the house. Furthermore, you can install exhaust fans at your windows or in the central air ducts to improve the efficiency of ventilation.

Using an air dehumidifier to reduce the relative humidity of the home. A high humidity level can promote the growth of mold and mildews, which give rise to spores, which can cause issues such as wheezing, irritation in the throat, difficulty in breathing, asthma, etc.

Avoid smoking or combustion of fuels inside the house, as these processes adversely affect the indoor air quality. Cigarette smoke contains several toxins, which can act as irritants to the airway and affect the respiration system, thereby triggering an asthma attack.

You can invest in an air purifier. The best method for reducing PM concentrations is by using an air purifier. Depending upon the size of the basement, an adequate air purifier should be used.
Air purifiers with HEPA (High-Efficiency Particulate Air) filters are best suited for indoor purposes. The presence of an activated charcoal filter and a UV light further increases the efficiency of the filters.

Other FAQs about Air quality that you may be interested in.

Can Air Pollution Cause Asthma?

Can Air Pollution Cause Cancer?

Does air quality worsen at night?

References

  • Volk HE, Lurmann F, Penfold B, Hertz-Picciotto I, McConnell R. Traffic-Related Air Pollution, Particulate Matter, and Autism. JAMA Psychiatry. 2013;70(1):71–77. doi:10.1001/jamapsychiatry.2013.266
  • Pagalan L, Bickford C, Weikum W, et al. Association of Prenatal Exposure to Air Pollution With Autism Spectrum Disorder. JAMA Pediatr. 2019;173(1):86–92. doi:10.1001/jamapediatrics.2018.3101
  • Becerra TA, Wilhelm M, Olsen J, Cockburn M, Ritz B. 2013. Ambient air pollution and autism in Los Angeles county, California. Environ Health Perspect121(3):380–386, PMID: 23249813, 10.1289/ehp.1205827.
  • Weisskopf, M.G., Kioumourtzoglou, MA. & Roberts, A.L. Air Pollution and Autism Spectrum Disorders: Causal or Confounded?. Curr Envir Health Rpt 2, 430–439 (2015). https://doi.org/10.1007/s40572-015-0073-9

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