Air Pollution Particles Can Reach the Placenta, Study Finds

Every time a pregnant person inhales a breath of polluted air, tiny particles may move through her body, lodging in the lungs, heart, or brain. Now, scientists know these pollutant particles can land in her placenta, and possibly the fetus.

In a September study published in Science of the Total Environment, researchers found evidence of particulate matter from traffic-related air pollution in the placentas of 15 healthy, pregnant women in London. 

The research, which was led by a team at Queen Mary University of London, indicates that particulate matter inhaled from the air can travel through the lungs to distant organs, reaching the placenta. 

“We suspected we would find some external particles in placental cells, but we didn’t expect to see them in all samples, so I guess that was the most unexpected,” Norrice Liu, MD, a pediatrician and clinical research fellow at Queen Mary University, who co-authored the study, tells Verywell via email. 

The study included women with exposure above the World Health Organization’s limit for particulate matter—2.5 PM. In an analysis of their placentas, researchers found black particles in an average of 1% of the cells. 

Adverse Health Effects

Most of these particles are carbon-based, but there were also traces of metals including silica, phosphorus, calcium, iron, chromium, and even titanium and zinc. Many of these materials can originate from the combustion of fossil fuels and additives in fuel and oil. Exposure to these particles can have negative health effects, including brain, heart, and lung damage. For expecting mothers, exposure to even low levels of air pollution during pregnancy could cause preterm birth or health defects in the child. 

This study did not verify whether the particulate matter can move to the fetus. However, Liu says if the placenta is damaged, it is likely that the fetus will be indirectly impacted as well.

"There is an established link between maternal exposure to air pollution and adverse fetal and birth outcomes such as preterm delivery and low birth weight at term,” Liu says. “This study suggests a potential underlying mechanism of how these are linked.”

The lungs and airways contain cells called phagocytes that patrol their environment for unwanted substances, and either destroy them or die with them. The research team found the pollutant particles embedded in phagocytes in the placenta. Liu says that it is possible that some of these particles escaped the placental phagocytes, which could allow them to move through the placenta and cause harm to the fetus. 

“An impaired placenta could result in less transport of nutrients and oxygen and removal of waste from the child and it could restrict the growth, cause preterm birth and preeclampsia,” Marie Pedersen, an associate professor of public health at the University of Copenhagen, tells Verywell via email. 

“Both prenatal development and pregnancy are life-stages of heightened vulnerability towards toxic exposures,” Pedersen, who was not affiliated with the study, says. “Factors such as exposure to ambient air pollution can have long-term effects on child and maternal health. If a child is born too light or too early, it may impact the function and health of the child throughout life, impacting the child, its family, and our society. Prevention of adverse pregnancy and birth outcomes is therefore very important.”

Source of Pollution

While combustion of fossil fuels makes up the majority of air pollution in the U.S., sources such as agriculture, residential buildings, and wildfires are also significant.

“The study is limited by its small size and it makes it difficult to accurately study correlations,” Pedersen says. “Although residential exposure to ambient air pollution reflects an important part of the external exposure, exposure during transportation, inside the home, and at other locations probably also contribute to the measured internal dose.”

Rebecca Schmidt, PhD, is leading a study called Bio-Specimen Assessment of Fire Effects (B-SAFE)—a several year-long investigation into how wildfires in Northern California impact the health of survivors. As part of the project, Schmidt, who is an assistant professor and molecular epidemiologist at the University of California, Davis, hopes to learn more about how exposure to smoke can affect pregnancy. 

“Is chronic air pollution—like traffic air pollution all year round because you live near a freeway—different than if you’re exposed to a brush fire or wildfire for a few weeks, or maybe nowadays, a couple months?” Schmidt asks Verywell. 

In the past few years, California has experienced wildfires that burn urban spaces as well as brush and trees. The smoke created by these fires can have different amounts and kinds of particulate matter, depending on what burns and at what temperature. Even when scientists only consider traffic-related air pollution, there can be significant differences in the composition of pollutants in cities around the world. 

“It’s hard to tease out the factors because people who are exposed to severe air pollution are also exposed to other environmental problems or injustices or stress,” Schmidt says. 

Regardless of the source many people who are exposed to high levels of air pollution experience inflammation—especially in the lungs—and elevated risk of cardiovascular disease. The bottom line, Schmidt says, is that air pollution can have clear adverse effects on one’s health, even if the exact particulate matter is unknown. 

In the U.S., people living along the west coast are likely to continue living with high exposure to smoke as wildfire season continues this month. In cities around the world, the particulates in air pollution from traffic and myriad other sources will continue to find their way into our bloodstream and organs.

Protecting Yourself From Pollution

In addition to finding methods to reduce the amount of pollutants in the air we breathe, scientists say it’s important to consider other solutions to protect our health. 

“Since it is unlikely that we can reduce all sources of ambient air pollution, more studies demonstrating protective effects of a diet rich in nutrients and other preventive measures, like use of air cleaning in the homes, are needed,” Pedersen says. 

Schmidt, who fears that annual wide-spread wildfires may be the new normal in California, says she is hopeful that researchers will find ways that the body is adapting to resist the harms of pollution. 

Although some studies suggest that exposures to high particulate matter may be associated with poor brain development, there's a lot scientists still don’t know about how environmental factors shape health outcomes for children. In the early stages of pregnancy, the epigenome—the collection of chemicals and proteins that help determine how genes are expressed—is wiped clean. During this period, the fetus has the opportunity to adapt to the environment it will be born into.

If the fetus is exposed to lots of particulate matter during that stage of its development, Schmidt says it’s possible its gene expression will be more adapted to an environment with high amounts of air pollution. While more research is needed to determine if this process works, she says this and other processes may be examples of how the body can protect itself from an early age.

“There is evidence out there, and it keeps building, about why we should be concerned and should look at this more,” Schmidt says. “But I also like to flip it and say, ‘there’s so much we don’t know yet, and we might find ways that people are resilient and there are benefits to learning that.”