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According to a 2017 UNICEF report, “nearly 17 million babies live in areas where outdoor air pollution is at least six times higher than international limits – potentially putting their brain development at risk simply because of the air they breathe.” 
Air pollution is one of the biggest threats to the health of our children worldwide. There is a significant volume of evidence that exposure to toxic elements in the air can affect the health and well-being of adults and children, with long lasting consequences.
It is well-known that air pollution not only worsens pre-existing conditions but also places our children at a higher risk of developing new respiratory problems including allergies, pneumonia, asthma, bronchitis and reduced lung function. The link between air pollution and respiratory health comes down to inflammation. Ultrafine particulate matter makes their way into airways and lungs, where it forces the body to launch an inflammatory response. Pollutants can also damage cardiovascular health and increase one’s risk of heart attack and stroke.
Fine particulate matter is a mixture of solid particles and liquid droplets present in the air. These particles are formed when different chemicals or pollutants (typically released from power plants, industries and vehicles) react with each other. Some of this matter like dust, dirt, soot, or smoke is large and noticeable. But some ultrafine particles (PM 2.5) in the air are so small that they can get into the lungs, cardiovascular system and even the brain, causing inflammation in the tissues.
What makes matter worse is that these contaminants in our air interact with other environmental factors such as diet, allergens and viruses – which further compounds the ill effects of the pollutants and snowballs into both known and unknown health problems.
Besides respiratory troubles, researchers are now realizing another ill-effect of air pollution on children. Studies show that this exposure may also impact their developing brain. This may manifest into a number of problems related to memory, learning, emotional development and mental health. This is scary, especially as many schools are located near busy roads, where children are constantly exposed to traffic related, and other source of, air pollution.
What makes young children more vulnerable to air pollution (and other toxins)?
Early childhood is a critical time when a child’s body is undergoing rapid growth and development. All major systems such as the brain, lungs and immune system are still in the process of maturation. If a child is exposed to toxins in air (or through any other environmental source), it can impair immunity, lung function and healthy brain development. This is bound to pose both short-term and long-term negative effects on aspects of health – including respiratory health, immune health and as we are now realizing, brain related health as well.
In addition, children breathe more air per unit of body weight than adults and spend more time outdoors, which means they end up inhaling more toxins. All of these factors mean that our children are more susceptible to the adverse effects of all-pervasive air pollution.
The effects of air pollution on brain development
Many studies have linked exposure to air pollution with adverse cognitive outcomes. The UNICEF report explains that the first 1,000 days of life are extremely critical for brain growth. This is the time when the brain forms neural connections that lay strong foundation for forming future neural connections. Healthy, functioning neural connections are important for developing healthy thinking, learning, memory, linguistic skills and motor skills in children. Contact with air toxins during this crucial time can impair this crucial development.
The report further explains that pollutants in the air can affect a child’s brain through many mechanisms; for example, through triggering inflammation in the brain and causing white matter in the brain to shrink.
Inflammation in the brain: Ultrafine particulate matters easily enter the bloodstream and can even cross the blood-brain barrier (BBB). It is a thin membrane that protects the brain from toxins. These ultra-small particles in the air we breathe can damage the integrity of the blood-brain barrier and cause inflammation in the brain.
The children and young adults exposed to fine particulate matter are shown to experience early neuro-inflammation, DNA damage, oxidative stress and immune changes (formation of neural antibodies that trigger auto immune responses and inflammation in the brain). As a result, children residing in polluted ‘megacity’ environments may develop inflammatory, degenerative changes in the brain that are typically associated with Alzheimer’s and Parkinson’s disease. This may result in a population more prone to develop neuro-degenerative disease early on in life.  
White matter damage: Polycyclic aromatic hydrocarbons (PAHs) belong to a class of air pollutants that are formed during incomplete combustion of organic materials. Exhaust from diesel powered vehicles, emissions from burning of oil and coal to generate heat and electricity, tobacco smoke, and space heaters all release and add PAHs into our environment.
A 2015 study found that prenatal exposure to PAHs can cause reduction in white matter of a child’s brain.  White matter fills up more than half of your brain. It contains millions of nerve fibres that connect neurons across different parts of the brain, creating neural connections responsible for cognitive abilities in early childhood and later years.
The changes in white matter were found to be related with slower cognitive processing and behavioural problems in children, and accompanied with their tendency to be fidgety, hyperactive and impulsive. The study found that damage to white matter is not limited to prenatal PAH exposure. Young children, when exposed to PAHs, also experienced similar outcomes.
The group has previously reported that exposure during pregnancy to airborne PAHs interfered with brain development of children in many ways – including “developmental delay at age 3 years, reduced full-scale and verbal IQ at age 5 years, and symptoms of anxiety, depression, and inattention on the Child Behavior Checklist (CBCL) at age 7 years, as well as slower processing speed on the Wechsler Intelligence Scale for Children IV (WISC-IV) at age 7 years”
Air pollution is affecting learning abilities in school kids
A 2018 study surveyed 90,000 schools across the Unites States and found that air pollution is putting school children at risks related to cognitive problems; affecting their ability to learn. The analysis also found that black, Hispanic and poor children bear the maximum brunt of these neurotoxins in the air.  The study author Dr Sara Grineski said, “We’re only now realizing how toxins don’t just affect the lungs but influence things like emotional development, autism, ADHD and mental health.” 
These results were consistent with other findings that also related exposure to contaminants in the air with impaired brain development, reduced working memory and other effects on cognitive functions.   
Prenatal exposure to air pollution
There is robust evidence that exposure during pregnancy can affect the developing brain of a foetus, which can result in potentially adverse outcomes in terms of preterm birth, birth defects, developmental delays and behavioural problems in later years (ADHD and autism).
A new study published in The Journal of Pediatrics found that women exposed to higher levels of fine particulate matter (PM 2.5), especially during the month before or after conception, were more likely to give birth to babies with congenital birth defects. 
The study concluded, “The most susceptible time of exposure appears to be the 1 month before and after conception. Although the increased risk with PM 2.5 exposure is modest, the potential impact on a population basis is noteworthy because all pregnant women have some degree of exposure.”
In a nutshell, exposure to higher levels of air pollution can impair healthy development of a child’s brain in many ways. This is known to cause developmental delays, behaviour problems linked with autism and ADHD; and impaired neural connections affecting optimal learning, memory and thinking.
- Nicholas Rees. Dangers in the Air. UNICEF. 2017 (A report by Division of Data, Research and Policy.
- LC Garciduenas et al. Air Pollution and Children: Neural and Tight Junction Antibodies and Combustion Metals, the Role of Barrier Breakdown and Brain Immunity in Neurodegeneration. Journal of Alzheimer's Disease, vol. 43, no. 3, pp. 1039-1058, 2015
- LC Garciduenas et al. Air pollution and children: barrier breakdown, inflammation, brain immunity and neurodegeneration. Journal of the Neurological Sciences 357(1):e509 · October 2015
- Peterson, Bradley S., et al. ‘Effects of Prenatal Exposure to Air Pollutants (Polycyclic Aromatic Hydrocarbons) on the Development of Brain White Matter, Cognition, and Behavior in Later Childhood’. The Journal of the American Medical Association Psychiatry, vol. 72, no. 6, 25 May 2015.
- Sara E.Grineski and Timothy W.Collins. Geographic and social disparities in exposure to air neurotoxicants at U.S. public schools. Environmental Research. 2018.
- Oliver Milman. Air pollution: black, Hispanic and poor students most at risk from toxins – study. The Guardian. 2018.
- Alvarez-Pedrerol et al. Impact of commuting exposure to traffic-related air pollution on cognitive development in children walking to school. Environ Pollut. 2017
- Sunyer J et al. Traffic-related Air Pollution and Attention in Primary School Children. Epidemiology. 2017
- Sunyer J et al. Association between traffic-related air pollution in schools and cognitive development in primary school children: a prospective cohort study. PLoS Med. 2015
- S Ren et al. Periconception Exposure to Air Pollution and Risk of Congenital Malformations. The Journal of Pediatrics. 2018.