Explained: Soot found in placenta, is foetus at risk?

The placenta is an organ attached to the wall of the uterus. It allows life-sustaining oxygen and nutrients to pass from the mother to the foetus. It lies on either end of the umbilical cord and has two sides, the maternal and foetal side. The study found tiny particles of black carbon accumulating on the side of the placenta that faces the foetus.

The particles were embedded in the placentas, implying that this had happened before the babies were born.

“We ruled out that our findings were just confounded by soot particles of the air which were on the surface of the placenta after birth,” environmental scientist Tim Nawhort of Hasselt University, Belgium, told The Indian Express in an email.

Black carbon particles are a key part of particulate matter. It is one of the byproducts from the burning of fossil fuels such as coal, oil, petrol and wood. Because of their small size, particulate matter, including black carbon particles, can be easily inhaled and can pass through the throat and into the rest of the body.

Previous studies have established a connection between prenatal exposure to ambient air pollution and impaired birth outcomes. None of the previous studies, however, had established that nanoparticles could cross the placental barrier as a result of inhalation in real-life settings.

How the study was conducted

The researchers chose 20 women in Northeast Belgium, 10 of whom were living in areas of high black carbon exposure and 10 in areas where exposure to black carbon was low. All the women were non-smokers. Additionally, five samples were taken from mothers who suffered miscarriages between 12 and 31 weeks of pregnancy.

For the first set of 20 women, the placentas were taken 10 minutes after the babies were born, and biopsies were carried out on both the maternal and the foetal sides. While black carbon particles were found in all samples, the amount varied by residential address — an average 9,500 particles per cubic mm for low-exposure areas and about 20,000 particles per cubic mm for high-exposure areas.

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Why it is a concern

The placenta is the sole point of contact between the mother and the foetus, carrying oxygen and nutrients from the mother’s blood supply to the foetus. Essentially, it is a temporary organ that keeps separate the mother’s and the baby’s blood supply, while also being a link between the two. The finding is a signal of the health effects that air pollution could have even before birth.

“Because the particles are at the foetal side of the placenta and this side interacts directly with the foetal blood flow, it is very reasonable to assume that the foetus is directly exposed,” Nawhort said. He added that soot particles may cause DNA damage and air pollution in general can impact cellular ageing, cognitive development and can lead to lower birth weight.

Lower exposure to air pollution is the only way that the foetus can be protected, he said.