Air pollution: Not all toxins equal; worst afflict children with anaemia, low birth weight

All air pollution is bad—but some pollution is far more dangerous than others.

Exposure to fine particle pollution (PM2.5) has been found to increase the risk of anaemia, acute respiratory infection and low birth weight among children in India, according to a study published in the journal Nature Communications.

For every 10 micrograms per cubic metre (ug/m3) increase in exposure to fine particulate matter, the risk of anaemia, acute respiratory infection and low birth weight in children increased by 10, 11 and 5 per cent, respectively, the researchers found.

The team from The Energy and Resources Institute (TERI), the Indian Institute of Technology (IIT), Delhi, and other institutes also suggested that using 'total PM2.5 mass' to measure exposure to air pollution could "substantially underestimate" the true combined effect of different components of PM2.5 on children's health in India.

PM2.5 is a mixture made up of various components with different sources and toxicities, they said.

Each polluting source may produce different PM2.5 components such as organic carbon (OC), nitrates (NO₃-), chlorides, along with metallic, soil and water molecules, and likewise, each component of PM2.5 may come from various sources, they said.

The researchers analysed health data from the National Family Health Survey (NFHS)-4, a household survey conducted between 20 January 2015 and 4 December 2016 across all 640 districts of India.

They chose low birth weight, anaemia and acute respiratory infection to represent the health burden of children aged 5 years or younger (under-5, or U5) because these parameters are commonly reported public health morbidities in India, they said.

Analysing more than 1,77,000 observations in the NFHS-4 dataset, the researchers found that elemental and organic carbon (OC), NO₃- and ammonia (NH₄+ ) were more associated with the three health outcomes than other PM2.5 species, even as, they said, other PM2.5 components also indicated a consistent risk to child health.

The national prevalence of low birth weight in the observations analysed was 16.6 per cent, with the prevalence being higher in girls (17.8 per cent) than in boys (15.5 per cent).

Low birth weight prevalence was found to vary with mother's education, socioeconomic status, mother's body mass index (BMI), age, place of residence, and different levels of PM2.5.

Anaemia was found to be prevalent among 56.8 per cent of the U5 children, and was also associated with maternal education, religion, socioeconomic, place of residence, levels of PM2.5 exposure and maternal anaemia status.

Acute respiratory infection prevailed in 2.8 per cent of the children studied, with rural areas showing higher estimated levels than urban ones, the researchers said.

At the sample collection level, the yearly average PM2.5 was found to be 62 μg/m³, with the most dominant components being OC, NO₃-, NH₄+ and sulphates (SO₄), along with others like chlorides, sodium, magnesium, potassium, calcium, soil and water molecules.

The fine particle pollution can also be divided by source, as domestic, industrial, international, agricultural and transport sectors, the researchers said.

Analysing the impact of sectoral PM2.5 on all three child health outcomes, the researchers attributed exposure to emissions from various sources: road dust, transport, industry, agriculture, domestic, and others, as well as international sources (from neighbouring countries).

Any of these types of exposure was found to have an adverse effect on at least one health endpoint.

The researchers said that the study presented the first comprehensive assessment of the effects of PM2.5, its components and the sectors contributing to it, with impact on the health outcomes of under-5 children in India.