Air Pollution,  Health,  Science,  Toxic Exposure,  Urbanization

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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2 Comments

  • Hayley Matthews

    I was not aware that simply living in the world today could put my future child at risk. It is upsetting to know that the pollution most would consider as a minute can reach the placenta; A place that is supposed to nourish and benefit a future child. Knowing that there is particulate matter in the placenta of healthy mothers is alarming, especially when you consider mothers who partake in certain risky habits such as smoking cigarettes. It would be interesting to know how the infant’s immune system is affected by prenatal cigarette exposure.

    In a research article that determined the effect of cigarette use on the infant immune system, it was determined that there was an increase in activity of mucosal immunity and health problems associated with IgA levels. In this study, the infant’s saliva and meconium were tested for SIgA levels. Children who were exposed to cigarette smoke had a higher level of IgA when compared to children who were not exposed to cigarette smoke.

    The results seem to show that the immune system function was overstimulated due to the pollutants, resulting in an immune system that never turned off. Although this may sound good in theory, an overactive immune system can lead to a variety of autoimmune diseases that are often hard to treat. Based on this information, it is clear that exposure to extreme pollutants such as cigarette smoke can have detrimental effects on children of all ages. Although all pollutants aren’t unavoidable, it is best to stay away from very harsh known pollutants such as cigarette smoke, industrial plants, and factories.

    https://pubmed.ncbi.nlm.nih.gov/29597003/

  • Ray Kinney

    City environments are typically highly polluted with the toxic metal lead, which is legacy from leaded paint degradation, leaded gasoline dispersal, and abrasion of lost vehicular lead wheel weights on pavement. Much of this lead contaminated dust becomes air borne to have greatly increased body uptake through the lung route, in addition to the ingestion and even the skin penetration dermal routes. Yes, escaping to cleaner environments can be very important for public health, but sadly, not even a financial possibility for millions of people that are then continuing to accumulate pollution and suffer devastating harm accumulating over time.

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