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Air pollution particles can cross to fetal side of the placenta, study finds

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Researchers found that the placentas of the women with the higher air pollution exposure were embedded with significantly more black carbon particles than the women with the lower exposure.

When air pollution particles — the sooty black carbon that’s emitted during the burning of fossil fuels such as gasoline and coal — are breathed in by pregnant women, they eventually reach and cross the placenta, according to a study published online Tuesday in the journal Nature Communications.

The study’s authors — a team of researchers from Hasselt University in Belgium — believe this disturbing finding may be the mechanism that explains the links that previous studies have found between pregnant women’s exposure to air pollution and a higher risk of poor birth outcomes, especially low birth weights and babies being born preterm.

“The key finding is that soot particles can enter the fetal part of the placenta, which means that during one of the most vulnerable stages of life, [when] organ systems are under full development, translocation of particles from the mother’s lungs to the fetus is possible,” said Tim Nawrot, the study’s senior author and a professor of environmental epidemiology at Hasselt University, in an interview with IFLScience.

“These particles cause inflammatory responses and might also react with the DNA,” he added.


The findings come as the Trump administration continues to roll back environmental regulations designed to protect against air pollution. Just this week, the administration announced plans to revoke California’s longstanding authority to set stricter air pollution standards for cars and light trucks.

How the study was done

The placenta is a temporary organ that develops in the uterus during pregnancy to provide nutrients and oxygen to the growing baby. It forms a protective barrier between the mother and the baby. Although the placenta was once believed to be impenetrable to chemical substances, research has shown that environmental pollutants, such as alcohol and drugs, can cross it.

In recent years, laboratory and animal studies have also suggested that tiny particles — such as black carbon — can also breach the placental barrier.

To see if they could find real-world evidence of this, Nawrot and his colleagues examined placenta from 28 women who were enrolled in the ongoing ENVIRONAGE birth cohort study. Women enrolled in that study have volunteered to donate their placentas for research after they give birth.

Ten of the women in the study lived during their pregnancies in areas of Belgium with relatively high levels of black carbon pollution, while 10 others lived in areas with relatively low levels.

Using a special high-resolution imaging technique, the researchers looked for and measured the amount of black carbon particles on the fetal side of the placentas. They found that the placentas of the women with the higher air pollution exposure were embedded with significantly more black carbon particles (an average particle count of 20,900 per cubic millimeter) than the women with the lower exposure (an average particle count of 9,500 per cubic millimeter).

Furthermore, the amount of carbon detected matched the women’s exposure. In other words, the higher a woman’s exposure, the higher the amount of black carbon particles found in her placenta.

Limitations and implications

This was a small study. The results will need to be confirmed among larger groups of pregnant women.


And although the study found that the black carbon particles had crossed the placenta, this study does not prove that the presence of such particles directly harms pregnancies or babies.

“Further research will have to show whether the particles can cross the placenta and reach the fetus, and if particle translocation is responsible for the observed adverse health effects during early life,” Nawrot and his colleagues point out in their paper.

Still, the study’s finding that black carbon particles can breach the placenta is troubling.

“It strengthens the hypothesis that direct effects induced by the presence of ambient combustion-related particulates are at least partially responsible for observed detrimental health effects from early life onward,” the researchers write.

It also underscores the need for stricter laws regarding air pollution.

“We need to develop air pollution standards which protect the most vulnerable of the population,” Nawrot told IFLScience.

FMI:  You can read the study in full on the Nature Communications website.

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