Placentas Are Caked in Soot from Car Exhaust. Could It Reach the Fetus?

Black soot spewn from cars and burning fossil fuels can find its way into the womb where a fetus is developing, according to a new study.

The researchers found that the amount of soot, also called black carbon, embedded in the fetus side of the placenta correlates to the estimated air pollution found near the expectant mother's home, they described online Sept. 17 in the journal Nature Communications. 

"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," said study co-author Tim Nawrot at Hasselt University in Belgium, in an interview with The Guardian. 

Even so, the researchers can't say whether those particles actually get into the fetus, they noted in the paper.

Toxic particles found floating in polluted air have been spotted in placentas before, and a study presented at a conference in 2018 revealed that inhaled black carbon — a component of soot — can enter the placenta through the mother's bloodstream. But previous research failed to confirm that the soot could then move from the maternal placenta, made from the mother's uterine tissue, to the part of the placenta made from tissues that form the developing child and so are accessible to the fetus. The new study supplies this evidence. 

The researchers gathered placental samples from more than 20 nonsmoking women in the Belgian town of Hasselt and exposed the tissue to ultrafast laser bursts, according to Science News. The technique excites negatively charged particles within each sample and causes different tissues to radiate colored light — red for collagen, green for placental cells and white for black carbon.

Related: 9 Uncommon Conditions That Pregnancy Could Bring

They found an average of 9,500 soot particles per cubic millimeter (about the volume of a grain of salt) in the placentas of women who lived a far distance from main roads and areas of high pollution, The Guardian reported. In comparison, women living in more polluted areas accumulated about 20,900 particles of black carbon per cubic millimeter on the fetal side of their placentas.

"There's no doubt that air pollution harms a developing baby," said Amy Kalkbrenner, an environmental epidemiologist at the University of Wisconsin-Milwaukee, who was not involved in the work, in an interview with Science News. A mother's exposure to air pollution has long been linked to heightened risk of preterm birth, low birth weight and miscarriage, but the dangers were attributed to inflammation in the mother herself, particularly in the uterus. The new study suggests "air pollution itself is getting into the developing baby," Kalkbrenner said. 

Metal contaminants, including lead, have been shown to cross the placental barrier and disrupt the development of the fetus and even lead to miscarriages and stillbirths, according to the National Institute for Occupational Safety and Health. Synthetic chemicals, including pesticides and flame retardants, can also transfer into the placenta and harm the fetus, scientists reported in 2016 in the journal Current Environmental Health Reports. 

"We should be protecting foetuses and this is another reminder that we need to get [air pollution] levels down," said Jonathan Grigg of Queen Mary University of London, whose lab conducted the 2018 black carbon study, in an interview with The Guardian. An estimated 91% of the world's population lives in regions where air pollution levels exceed the recommended World Health Organization maximums; this study highlights yet another risk of letting those levels go unchecked, he said. 

• 8 Ways That Air Pollution Can Harm Your Health 
• 5 Reasons Why Placentas are Awesome 
• Having a Baby: Stages of Pregnancy 

Originally published on Live Science.