Smog hangs over a bridge on the Yamuna in Delhi. Photo: Midhun Vijayan / CSE

India’s capital Delhi was the worst-affected among all places that have a cancer registry in the country, according to the latest available data by the National Cancer Registry Programme from 2012 to 2016. In children between the ages of 0 and 14 years, the proportion of childhood cancers relative to cancers in all age groups varied between 0.7 per cent and 3.7 per cent.

Could air pollution be responsible? There is enough evidence to show that exposure to air pollution can lead to cancer in adults. But this correlation is not studied much in children.

Children would be more at risk considering that they breathe more rapidly than adults and absorb more pollutants. Also, they live closer to the ground, where pollutants tend to accumulate.

Generally, research studies across the world show that exposure to air pollution is linked to acute myeloid leukemia (AML) and non-Hodgkin lymphoma. Pollutants such as benzene, NOx and particulate matter have been identified as culprits in childhood non-Hodgkins lymphomas.

A study published in January 2023 in the journal Nature reported an association between exposure to PM2.5 level and risk of Acute lymphoblastic leukemia among children.

Delhi and north India 

The magnitude of the disease burden being carried by Delhi’s children is apparent when one compares it with Pasighat in Arunachal Pradesh. As many as 203.1 boys per million are affected by all the broad kinds of cancers in Delhi, compared to just 12.2 per million in Pasighat.

Other cities in north India — the country had 28 Population Based Cancer Registries between 2012 and 2016 — did not fare better. For instance, Patiala’s cancer registry reported 121.2 cases per million boys. Mumbai on India’s western shore, which too is currently reeling under pollution, stood at 10th place.

In case of girls between the ages of 0-14, the number is 125.4 per million in Delhi compared to 12.1 in East Khasi Hills District. Patiala stood at ninth position, with 74 cases per million.

The data shows that Delhi has a high number of leukemia cases too. As many as 84.2 boys per million, between the ages of 0-14 are affected, compared to just 7.3 per million in Meghalaya. For girls, this number stands at 47.2 cases per million, the second-highest after Manipur’s Imphal West District, compared to just 4.9 per million in Assam’s Cachar district.

In case of lymphomas, the number stands at 30.7 per million for boys in Delhi, much lower than the 2.3 per million cases seen in Meghalaya. For girls, Delhi has the third-highest cases of lymphomas which stand at 10 per million.

The report also shows that boys in Delhi have the highest cases of cancer per million, followed by China’s Jianmeng among Asian countries studied. In case of girls, the city has the sixth-highest number of cases.

For all countries included in the study, Delhi has the sixth-highest number of cancer cases for boys and tenth highest in case of girls.

In the womb

Researchers are also trying to understand the impact of air pollution on children exposed early to air pollution as unborn babies get everything they need to grow in their mother’s womb through the placenta.

In 2013, a study found a co-relation between early exposure to traffic pollution and several childhood cancers but suggested that more studies are needed to confirm the relation.

One such study is underway in the United Kingdom, where researchers are trying to study the impact of road traffic pollution on babies by studying placentas. They want to see if pollutants in the mother’s blood can cross the placenta into the baby’s blood. They will also study cord blood for the presence of chemicals and tiny particles which make up air pollution from road traffic.

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