'Childhood cancers doubled in Delhi in 25 years, when city's air quality also became toxic'

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About 14 years ago, a group of scientists from Kolkata did an extensive analysis of the health impacts of vehicular pollution, particularly for children. The findings of the study were shocking and underlined the need for urgent measures to save the future of our progenies. The lead scientist of the study, Manas Ranjan Ray, former assistant director and head, department of experimental haematology, Chittaranjan National Cancer Institute (CNCI), Kolkata, talks to Down To Earth about the seminal work and what has changed since then.

Edited excerpts: 

Preetha Banerjee: Your research indicates that air pollution is a significant external threat to child health and development. Could you elaborate on how children, especially in regions like North India, are impacted by this threat?

Manas Ranjan Ray: About 93 per cent of the children of the world under the age of 15 years (1.8 billion) breathe toxic air that adversely affect their health and development. Sadly, many of them die. In 2016, for instance, 600,000 children died from acute lower respiratory infections caused by polluted air mostly in the developing nations (WHO 2018).

Air quality in north India and the Gangetic delta usually hovers from “poor” to “severe” category. The situation takes a more serious turn at the onset of monsoon as stubble burning adds more pollutant in air. Against this background, the first comprehensive epidemiological study on air pollution and children’s health in northern and Eastern India was conducted by Chittaranjan National Cancer Institute (CNCI), Kolkata. The findings were shocking: children’s health was found seriously impacted by airborne pollutants from mother’s womb to their adulthood.

Ambient air pollution mainly from vehicular traffic was found to increase the risk of smaller babies during pregnancy, pre-term birth that increases the risk of different health problems later in life, spontaneous abortion, stillbirths and low birth weight of the infant (less than 2.5 kg).

Traffic-related air pollution (TRAP) was found to increase the risk of several types of adverse health outcomes for school-age children. For example, it affects a child’s lung function and lung development. Gound-level ozone (O3), a secondary pollutant, along with nitrogen dioxide (NO2) and fine particles (PM 2.5) released from the tail pipes of the automobiles were the main offenders.

PM2.5 and oxides of nitrogen (NOx) including NO2 increase the risk of respiratory infections in children, resulting in acute lower respiratory infections including pneumonia that could be fatal, among others.

Almost every organ system of the body is affected. The CNCI study observed a link between traffic-related volatile organic compounds, mainly benzene, in Kolkata and Delhi’s air with increased risk of childhood leukaemia.

Studies have shown that children in urban and suburban areas had the highest exposures to UFPs in contrast to children in rural areas. UFPs can even break the blood brain barrier (a high security system to protect the brain from any external onslaughts) affecting children’s brain development, that may culminate into cognitive impairment (low IQ), behavioral problems (attention-deficit hyperactivity disorder, ADHD) and some types of Autistic Spectrum Disorders (ASD).

PB: Why are children more at risk to air pollution exposures?

MRR: In the womb, they are vulnerable to their mothers’ exposure to pollutants, both outdoors (ambient) and indoors (household). Thus, a child’s susceptibility to air pollution can begin as early as in utero when all the important organ systems like endocrine (hormonal), reproductive, immune, visual and nervous systems are developing. Exposures to pollutants and resultant injury during these “windows of susceptibility” can impact the child’s health later in life.
Children’s respiratory systems (lungs and the airways) are still developing, they are not yet mature enough to cope with the onslaught of oxidant-induced injury by toxic air pollutants. Coupled with this, they have an underdeveloped detoxification machinery with weak antioxidant defence that may result in permanent alterations in the lungs.

Children breathe faster than adults. Because of their growing age, their metabolic rate is higher than the adults. Their cells require more oxygen. Accordingly, they inhale relatively more air (ml/ kg body wt), than the adults. Thus, when the air is highly polluted, like that in Indian cities, it will be more injurious to children’s health.

Manas Ranjan Ray. Photo: @CBhattacharji / X (formerly Twitter)

The problem is compounded by the facts that children are more physically active, their metabolic rate is higher requiring more air per kilogram of body weight. Accordingly, their breathing rates are higher (20-30 breaths per minute compared with 12-16 breaths / min in adults), taking in more air and, with it, more air pollutants.

An additional handicap is their ineffective nasal filtering capacity to exclude a chunk of pollutants in the PM10 range.

They take in a larger fraction of air through their mouths than the adults. Due to this increased oral breathing, the pollution penetrates deep into the lower respiratory tract.

Due to their shorter height, children breathe air closer to the ground where some pollutants including PM10 and PM2.5 are present in highest concentrations.

Furthermore, children’s immune system is underdeveloped and not fully operational. The net result is that they became more vulnerable to airborne pollutants than the adults.

Inhaled ultrafine particles (PM0.1) are so small that they can enter the bloodstream and cause the degeneration of blood-brain barrier, leading to oxidative stress, neuroinflammation and brain damage. As the blood-brain barrier is still developing in children, they become more vulnerable to neurobehavioral disorders.

PB: Are there any specific pollutants that are more harmful for children?

MRR: For respiratory complications such as common cold, cough, rhinitis, asthma and lung function reductions, the most harmful pollutants are ground-level ozone (O3) and nitrogen dioxide (NO2) in short term and PM2.5 for long-term exposures.

For neurological complications, ultrafine particles (PM having a diameter of less than 0.1 mm or 100 nano meter) are most dangerous as they can reach the brain by invading blood-brain barrier.

For childhood cancers, the most harmful pollutants are benzene and benzo(a)pyrene released from vehicular traffic and burning of unprocessed biomass fuels.

PB: Tell us about your seminal 2010 study on the impact of air pollution on children in Delhi. What were some of the major observations?

MRR: We conducted an epidemiological study, with the help of Central Pollution Control Board, Delhi, on the impact of Delhi’s air pollution on children’ health. The four-year case-control study (2002-2006) included a total of 16,164 school-age children, 11,628 (boys 7,757 and girls 3,871) from Delhi and 4,536 from rural West Bengal and Uttarakhand as control. The median age of the children was 13 years (range 4-16 years).

Compared with controls, children in Delhi had significantly greater prevalences of both upper and lower respiratory symptoms (URS and LRS, respectively), asthma and reduced lung function. About one-third (32.1 per cent) of the children in Delhi complained of frequent sore throat, common cold with fever, sinusitis, runny nose and sneezing against 18.2 per cent in controls. Similarly, LRS like sputum-producing (wet) cough, dry cough, wheeze and chest pain or tightness were more prevalent in Delhi (17.0 vs 8.0 per cent in control). Asthma was present in 4.6 per cent children of Delhi against 2.5 per cent in control. In addition, Delhi’s school children suffered more from recurrent eye irritation (14.7 vs 4.2 per cent in control group), headache (27.4 vs 11.8 per cent), nausea (11.2 vs 5.6 per cent) and fatigue (12.9 vs 6.7 per cent).

The study documented remarkable negative impact of the city’s polluted air on children’s lung function. Overall, lung function was significantly reduced in 43.5 per cent children of Delhi compared with 25.7 per cent in control. Girl students of Delhi suffered more than the boys (51.0 vs 39.8 per cent). Microscopical examination of their sputum showed inflammation of the airways. A sizeable number of Delhi’s school children enrolled in this study were overweight (5.4 vs 2.4 per cent in control) and hypertension was 3-times more prevalent than the controls (6.2 vs 2.1 per cent).

Delhi’s air pollution was also found adversely affecting the behavior of the children as attention-deficit hyperactivity disorder (ADHD) was detected in 6.7 per cent children against 2.7 per cent in children of the control group. ADHD children are impulsive, overactive, inattentive, easily distracted and having poor academic interest.

The study was an eye-opener. It firmly established, for the first time, that Delhi’s air pollution is affecting both the physical and mental health of its children.

PB: How have things changed since that study was published, in terms of both policies and findings? What are your latest observations?

MRR: Delhi’s air pollution, after a short period of improvement following introduction of CNG for public transport vehicles, has remained a matter of concern. Also, several other cities in India are now competing with Delhi for the dubious distinction of number one position in nation’s pollution map.

Against this backdrop, epidemiological studies with sensitive health parameters in a large cross-sectional population, like we did, should have been carried out at regular intervals to get an idea of the current situation. It is also required to assess whether the various pollution-abatement schemes of the government and other agencies are giving the desired benefits to the people or not.

Unfortunately, I have not come across in the past decade any such large, field-based comprehensive study in Delhi or elsewhere in the country. Admittedly, there have been a handful of studies conducted either by the scientists or by some clinicians (not a team comprising of both!) with a relatively small sample size and even smaller goals (health end-points). The majority of the published studies in the past few years rarely portrayed the overall picture of public health problems, particularly that of children’s health, vis-à-vis current air pollution scenario of Delhi or any other highly polluted Indian cities in the Gangetic plains.

PB: Is our healthcare system equipped to deal with the health crises wrought by air pollution? What do you think should be done?

MRR: Polluted air is poisoning millions of children, adolescents and adults and ruining their lives. The high burden of deaths and diseases due to air pollution is also impacting India’s economy. Admittedly, the healthcare system of India has improved substantially in the past few decades. Now we have three-tier system of public health care centers in the villages, district hospitals, and tertiary care hospitals in the cities. However, the government expenditure in Indian health care system is inordinately low and, overall, the system is heavily dependent on out-of-pocket expenditure and private health care set ups. Thus, the affordability and accountability of the health care system for the low- and middle-income people are in question. Therefore, the entire health care set up of the country from the village level needs to be restructured in order to provide speedy, appropriate, adequate, and affordable care to the common people who are facing a severe threat to their life from air pollution.

PB: How has childhood cancer incidence changed over the years? What role does air pollution have to play in the trend?

MRR: In 2013, the International Agency for Research on Cancer (IARC) has classified ambient air pollution as a Group 1 carcinogen for humans. Cancer risk increases with increasing PM2.5 levels and VOCs such as benzene in breathing air.

Information on recent cancer statistics is important for planning, monitoring and evaluating cancer control activities. Unfortunately, current data on childhood cancer burden in India is lacking.

The data available from National Cancer Registry Programme Report 2020, documented the cancer incidence from 28 Population-Based Cancer Registries (PBCRs) for the years 2012-2016. This was used as the basis to calculate cancer estimates in India. However, PBCRs do not give us a comprehensive pan-India picture as they have a clear urban bias, since paediatric oncology services in India are predominantly located to a handful of tertiary care centres in major cities.

Also, the PBCRs covered only about 10 per cent of the population of India and data from some of the populous states like Uttar Pradesh and Bihar are presently unavailable for analysis. In essence, we hardly have any data on childhood cancer from rural and semi urban India. It is therefore needed that cancer registration be expanded to include a more representative population in each state of India for reliable projections and to strengthen cancer control activities.

The age-adjusted incidence rate of childhood cancers per million (AARpm) in different regions of the country, as reported in PBCR, varied significantly. Delhi showed the highest AARpm for all types of childhood cancers both in boys and girls. It was 235.3 in boys and 152.3 in girls, compared with 156.7 for boys and 85.6 for girls in Chennai and 136.1 for boys and 88.7 for girls in Aizawl.
The increase in childhood cancer in Delhi from 1990-2014 has been remarkable: 97 per cent rise in boys and 93 per cent in girls (Malhotra et al. 2021). In essence, the prevalence of childhood cancer has increased by nearly 100 per cent over these 25 years in Delhi. In these 25 years, 8,484 new cases were registered in boys, compared to 4,153 cases in girls.

PB: What are some of the biggest triggers of childhood cancer in the country?

MRR: Among the gaseous pollutants are volatile organic compounds (VOCs) such as benzene, toluene, and xylene. There is evidence that these compounds affect human health; for instance, benzene increases the risk of cancer in the bone marrow (leukemia) and lymphatics (lymphoma).

Although not currently regulated through air quality standards, they are the tiniest PM with aerodynamic diameter of less than 0.1 microns (below 100 nm).

They have high number concentrations, larger surface area/mass ratio, enhanced oxidative capacity and ability to translocate into systemic circulation. UFPs have high deposition efficiency in the innermost regions of the lungs (alveoli), can penetrate the alveolar epithelium to reach the pulmonary interstitium (space between the lungs and the adjoining blood vessels) and gain access to the blood. Now they can reach every part of the body, including the brain causing an array of health damages including the development of some malignancies.

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