A new study, led by a team from The Stockholm Environment Institute (SEI) at the University of York, has found that in 2010, about 2.7 million preterm births globally—or 18% of all pre-term births—were associated with outdoor exposure to fine particulate matter (PM2.5).The open-access study is published in the journal Environment International.
There are many known risk factors for preterm birth—from the mother’s age, to illness, to poverty and other social factors. Recent research has suggested that exposure to air pollution could also be a risk factor. The researchers combined national, population-weighted, annual average ambient PM2.5 concentration, preterm birth rate and number of livebirths to calculate the number of PM2.5-associated preterm births in 2010 for 183 countries.
Uncertainty was quantified using Monte-Carlo simulations, and analyses were undertaken to investigate the sensitivity of PM2.5-associated preterm birth estimates to assumptions about the shape of the concentration-response function at low and high PM2.5 exposures, inclusion of provider-initiated preterm births, and exposure to indoor air pollution.
|Percentage of total preterm births which were associated with ambient PM2.5 in 2010 using a low concentration cut-off of a) 4.3 μg m−3, and b) 10 μg m−3. Malley et al. Click to enlarge.|
This study highlights that air pollution may not just harm people who are breathing the air directly—it may also seriously affect a baby in its mother’s womb. Preterm births associated with this exposure not only contribute to infant mortality, but can have life-long health effects in survivors.—Chris Malley, a researcher in SEI at York and lead author
When a baby is born preterm (at less than 37 weeks of gestation), there is an increased risk of death or long-term physical and neurological disabilities. In 2010, an estimated 14.9 million births were preterm—about 4–5% of the total in some European countries, but up to 15–18% in some African and South Asian countries.
The study revealed that while many other health impacts of air pollution have been documented—most notably through the Global Burden of Disease studies—the focus has been mainly on premature deaths from heart disease and respiratory problems.
The new study adds an important new consideration in measuring the health burden of air pollution and the benefits of mitigation measures, Malley said.
A pregnant woman’s exposure can vary greatly depending on where she lives—in a city in China or India, for instance, she might inhale more than 10 times as much pollution as she would in rural England or France. The study did not quantify the risk in specific locations, but rather used the average ambient PM2.5 level in each country, and analyzed the results by region.
India alone accounted for about 1 million of the total 2.7 million global estimate, and China for about another 500,000. Western sub-Saharan Africa and the North Africa/Middle East region also had particularly high numbers, with exposures in these regions having a large contribution from desert dust.
SEI is working to support more than 20 developing countries in Africa, Asia and Latin America to develop plans to reduce emissions leading to particulate air pollution.
It is important to realize that action needs to be taken on all the major sources. In a city, maybe only half the pollution comes from sources within the city itself—the rest will be transported there by the wind from other regions or even other countries. That means that often regional cooperation is needed to solve the problem.—Dr Johan C.I. Kuylenstierna, co-author of the study and SEI’s director of policy
The analysis grew out of SEI’s Initiative on Low Emission Development Pathways (LED-P), which includes the development of a “benefits calculator” to help policy-makers and planners assess the potential benefits of undertaking measures that reduce air pollution.
This work in LED-P is contributing to the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants (CCAC), where SEI is working with UNEP and other partners to support more than 20 developing countries in Africa, Asia and Latin America to develop plans to reduce emissions leading to particulate air pollution.
Global modelling and satellite data analysis were conducted by Daven Henze, co-author of the study from University of Colorado, Boulder, through his membership on the NASA Air Quality and Applied Sciences Team (AQAST).
PM2.5 particles include a variety of substances, such as black carbon (soot), sulphates, nitrates and ammonium, as well as dust from soil and from industrial processes such as cement production.
To reduce the PM2.5 problem, you need to control many different sources, but in many developing countries, certain emission sources dominate. This includes emissions from cooking with biomass fuels (which is also associated with very harmful indoor pollution), diesel vehicles and other transport, and particles emitted when agricultural residues are burned in fields. Forest fires also contribute to ‘regional haze’.—Dr Kuylenstierna
Christopher S. Malley, Johan C.I. Kuylenstierna, Harry W. Vallack, Daven K. Henze, Hannah Blencowe, Mike R. Ashmore (2017) “Preterm birth associated with maternal fine particulate matter exposure: A global, regional and national assessment,” doi: 10.1016/j.envint.2017.01.023