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The unborn baby: Healthy pregnant mothers exposed to air pollution from road traffic inhale toxic particles that may end up in the placenta

By Roberta Attanasio

According to a recently published study, carbon and metal particles from road traffic, once inhaled, reach one of the many places where we would rather not find them—the unborn baby’s life support system, best known as placenta.

Lead author Jonathan Grigg said: “Our study for the first time shows that inhaled carbon particulate matter in air pollution, travels in the blood stream, and is taken up by important cells in the placenta.” For the study, researchers analyzed placentas from 15 healthy non-smoking women, donated after the birth of their children. All women delivered healthy babies. However, they lived in an environment that exposed them to high levels of particulate matter originating from urban traffic. Indeed, the particles observed in the placental cells closely resemble—in size, shape and composition—those emitted by traffic-related sources or formed from them.  

Particulate matter (also called particle pollution) is a mixture of solid particles and liquid droplets found in the air, which come in many sizes and shapes and are made up of hundreds of different chemicals. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope. Some particles are emitted by construction sites, unpaved roads, fields, smokestacks or fires, but most form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries and automobiles.

The researchers found—within the placental cells—not only carbon particles, but also particles containing carbon with a mixture of chemicals found in vehicle exhaust, such as iron, phosphorus, calcium, silica, aluminum, titanium, chromium, and cerium, which arise from fuel and oil additives. How did these particles get into the placental cells? Particles present in air pollution are inhaled, and then from the lungs translocate to distant organs through the blood stream. Macrophages and trophoblasts— the primary resident phagocytes in the placenta—pick them up. Phagocytes are cells of the innate immune system also known as the “big eaters”—they engulf the particles with the aim of “cleaning up” the placenta.

Lisa Miyashita, a study co-author, said: “We have thought for a while that maternal inhalation could potentially result in pollution particles traveling to the placenta once inhaled. However, there are many defense mechanisms in the lung that prevent foreign particles from traveling elsewhere, so it was surprising to identify these particles in the placental cells from all 15 of our participants.”

Why is it worrisome to find particulate matter in placental cells? “The placenta is a distinctive and defining anatomical characteristic of mammals. Composed primarily of fetal tissue, it is the conduit through which maternally produced nutrients and oxygen enter the fetus, and metabolic waste products return to the mother for excretion. It also enables a developing baby to guide pregnancy, from assisting in embryo implantation to helping maintain the gravid state and instructing the mother’s body about what is needed for its well-being. Placental signaling can even calibrate the rate of fetal growth and influence the length of the pregnancy.”

Particulate matter could adversely affect the unborn baby, especially heart and brain, although more research is needed to confirm these concerns. Fiona Miller Smith, Chief Executive of Barts Charity in the UK, the organization that funded the study, said: “This is an incredibly important study and immensely relevant to mums-to-be in our local community, indeed in any urban community anywhere in the world.”

Photo by John Arano on Unsplash

These results are, unfortunately, not surprising, as another study showed last year that black carbon particles—a component of particulate matter derived from combustion—accumulate on the fetal side of the placenta. The study, which included 25 placentas from non-smoking women, also showed that the number of particles on the fetal side of the placenta correlated with the air pollution levels experienced by the mothers. The placentas of mothers who lived near main roads contained and average of 20,000 particles per cubic millimeter, whereas those from mothers who lived further away contained an average of 10,000 particles per cubic millimeter. Tim Nawrot, lead study author, told The Guardian: “This is the most vulnerable period of life. All the organ systems are in development. For the protection of future generations, we have to reduce exposure.” He said that while governments had the responsibility of cutting air pollution, people should avoid busy roads when possible.

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Author: Roberta Attanasio

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