The impact of air pollution on children’s health begins even before they are conceived. It starts by impairing the fertility of both men and women. Research shows that exposure to air pollution affects ovarian reserve in women. The study conducted on women in China showed that the level of anti-müllerian hormone—a predictor of ovarian reserve—changed by -8.8 per cent, -2.1 per cent, -1.9 per cent and -4.5 per cent per 10 μg/m3 increase in PM1, PM2.5, PM10 and nitrogen dioxide (NO2). “Theoretically, PM with smaller size and larger surface area volume ratio, e.g. PM with diameter ≤1 μm (PM1), is more likely to penetrate through the alveolar capillary barrier and then impact directly the ovarian function via blood circulation,” notes the paper published in Environmental Research on February 1, 2023. Though the underlying mechanism of female fertility decline caused by air pollutants remains unclear, limited evidence speculates that oxidative stress and inflammatory response caused by air pollution may be one crucial pathway, the researchers say.
Similarly, a study in China on 33,876 men showed that exposure to PM2.5 and PM10 decreased total and progressive sperm motility. The findings were published in JAMA Networks on February 17, 2022.
If the child is conceived against all odds, air pollution can hinder their development in the uterus as pollutants can cross the placenta into the baby’s blood. In the study published in the Journal of Family and Reproductive Health in June 2017, the researchers from Iran have found an inverse relationship between the exposure to air pollution in the first trimester of pregnancy and the weight of placenta, which sustains the development of the foetus.
A comprehensive review of studies, published in The Lancet Planetary Health reports the presence of black carbon particles in cord blood which enter foetal liver, lungs and brain. The presence of the pollutants continues to harm the growing foetus so much that it tends to increase the risk of preterm birth. This, in turn, can increase the chances of stillbirth, low birthweight, underdeveloped lungs in the baby, and death of the baby during or shortly after birth.
Sudhir Gupta, former chairperson of the department of gynaecology at Baba Raghav Das (BRD) Medical College, Gorakhpur, explains how air pollution affects the development of foetus, “Due to pollution, pregnant women cannot get enough oxygen from the ambient air, which affects the natural development of the foetus. Furthermore, the higher the sulphur contents in the air, the greater the risk of miscarriage,” he says. Bhupendra Sharma, chairperson of the paediatrics department of BRD Medical College, says, “Air pollution can also lead to anaemia in expectant mothers, which greatly reduces the chance of delivering a healthy baby.”
If the child survives the onslaught of pollutants in the utero, multiple studies show that the exposure before and after birth can impair their neurodevelopment skills, such as intellectual functioning, memory and learning, attention and executive functions, verbal language, numerical ability and motor and/or sensor motor functions. “The pollutants that seem to represent the greatest risk are PM2.5, NO2 and PAHs [polycyclic aromatic hydrocarbons],” states a review of 30 research papers, published in Neuroscience & Behavioral Reviews in May 2022.
Just like in adults, the child’s blood pressure is known to shoot up due to exposure to air pollution during pregnancy—higher the mean PM2.5 and black carbon exposure during the third trimester, higher the newborn’s systolic blood pressure.
Exposure to air pollution in utero can also lead to congenital heart defects in children, making survival difficult. Lungs, too, are not spared from the onslaught. It has been observed that higher the exposure to air pollution during infancy, lower the lung capacity. Acute respiratory infections too seem to affect children who are more exposed to PM2.5. A survey of under-five children indicates that a 10 μg/m3 increase in PM2.5 was associated with greater chances of contracting an infection.
Gut health too gets affected—pollutants inhaled during the first six months of life adversely affect the composition of gut microbes which could increase risk of allergies, obesity and diabetes, and even affect brain development. A 2020 study published in Gut Microbes states that these microbes and their by-products shape appetite, insulin sensitivity, immunity, mood and cognition, and a poor mix of microbes can leave the child prone to asthma, type 2 diabetes and other chronic illnesses.
Exposure to air pollution in the womb can also change the protein activity of the baby. For example, pollutants have been found to affect cell processes such as autophagy, “self-eating” of damaged cells that usually occurs in response to stress, according to a study presented at the European Respiratory Society International Congress in Milan, Italy, on September 12, 2023. Exposure to higher NO2 was linked to decreased levels of SIRT1, a protein that plays a protective role in stress resistance, inflammation and ageing.
Evidence is also mounting around the impact of pollution sources on health. Studies in Europe have investigated the impact of vehicular emissions on child health and impact on neuron development along the highways. In 2013, a study found correlation between early exposure to traffic pollution and several childhood cancers.
And as if to complete the circle of destruction, exposure to air pollution also impacts the reproductive health of adolescent girls. Higher exposure to particulate matter in utero and throughout childhood has been implicated in the early onset of menarche because these particles seem to have endocrine-disrupting properties.
This was first published as a part of a cover story on the impacts of air pollution on children in the 1-15 December, 2023 print edition of Down To Earth