Early-Life Exposure to Ambient Fine Particulate Air Pollution and Infant Mortality: Pooled Evidence from 43 Low- and Middle-Income Countries

Each year, over 2.5 million children die within the first 28 days of birth, with three out of four of these neonatal deaths occurring in Southern Asia and sub-Saharan Africa. At the same time, many low- and middle-income countries are becoming increasingly exposed to adverse environmental stresses such as ambient fine particulate air pollution, which refers to pollution in outdoor environments. Given estimates from the World Health Organization (WHO) that over 4.2 million deaths worldwide can be attributed to ambient air pollution, rising pollution is likely contributing to the high rates of neonatal and child mortality in low- and middle-income countries.

Due to the scarcity of studies in low-income settings where ambient air pollution is very high, most previous studies estimate global mortality due to ambient air pollution using data on active smoking and second-hand smoke in high-income countries. In a new International Journal of Epidemiology article, Mahesh Karra, Nihit Goyal and David Canning improve on this evidence by compiling a global sample of individual-level child data from a wide range of low- and middle-income settings. They then match child mortality data to the local ambient pollution level when the children were in utero and in their first year after birth.

Main findings:

• The results show early-life exposure to overall ambient air pollution does not have a strong association with infant mortality.
• However, the association changes when pollution is disaggregated by source: the association between early-life pollution exposure in the form of dust and sea-salt, which make up over half of all fine particulates, and mortality is weak. However, other types of fine particulates created by human activity are strongly associated with neonatal mortality, even at low levels of exposure.

The study does not identify the biological mechanism through which exposure to pollution may affect child mortality. Nevertheless, policies that aim to reduce ambient air pollution in low- and middle-income countries could contribute significantly to reducing neonatal mortality from the level of 28 per 1,000 births observed in the sample and meeting the Sustainable Development Goal of lowering global neonatal mortality below 12 per 1,000 children by 2030. Furthermore, the study results suggest that the current WHO guideline of limiting the overall ambient pollution level should be augmented with a lower limit for harmful human-caused carbonaceous pollution.