Toxic carbon particles from air pollution can travel to placentas putting lives of unborn babies at risk: Study
Soot or tiny particles of black carbon have been found on the fetal side of the placenta of women exposed to air pollution during pregnancy, according to an observational study involving 28 women.
The toxic particles—released every day into the air, mainly due to the burning of fossil fuels—are able to travel through the lungs of pregnant women and reach the fetal side of the placenta, according to evidence from the study, indicating that unborn babies could be directly exposed to them.
According to the researchers led by Professor Tim Narwot from Hasselt University, Belgium, the results demonstrate that the human placental barrier is not impenetrable for particles. The findings have been published in Nature Communications. "Our study provides compelling evidence for the presence of black carbon particles originating from ambient air pollution in human placenta and suggests the direct fetal exposure to those particles during the most susceptible period of life," says the research team.
While the toxic particles have been linked with pre-term births or low birth weights, understanding how they affect pregnancy—through direct effects on the fetus or indirect effects through the mother—is critical to improving pregnancy care in polluted areas, says the research team.
Using high-resolution imaging, the researchers were able to detect black carbon particles in placentae collected from five pre-term and 23 full-term births. The team found that 10 mothers who lived closest to major/busy roads (less than or equal to 500m) and had been exposed to high levels of black carbon particles (2.42 micrograms per m3) during pregnancy had higher levels of particles in the placenta, as compared to 10 pregnant women who had been exposed to low levels of residential black carbon (0.63 micrograms per m3), and lived more than 500m away from a major road.
"The presence of black carbon particles could be identified in all screened placentae, and a positive association has been found between the placental black carbon load and the mothers' residential black carbon exposure averaged over the entire pregnancy," says the study.
The placenta is an organ that develops in the uterus during pregnancy. The placenta attaches to the wall of the uterus and is connected to the baby by the umbilical cord. Blood from the mother passes through the placenta, filtering oxygen, glucose, and other nutrients to the baby via the umbilical cord. It also removes waste products from the baby's blood.
The new study adds to existing evidence on the dangers of pollution for unborn babies and suggests that when pregnant women breathe polluted air, sooty particles are able to reach the placenta via the bloodstream.
Last year, research presented at the European Respiratory Society International Congress showed evidence that soot, typically created by burning fossil fuels, has been found in placentas. The team studied a total of 3,500 placental macrophage cells from the placentas of five pregnant women and examined them under a high-powered microscope. They found 60 cells that between them contained 72 small black areas that researchers believe were carbon particles. On average, each placenta contained around five square micrometers of this black substance.
"We do not know whether the particles we found could also move across into the fetus, but our evidence suggests that this is indeed possible. We also know that the particles do not need to get into the baby's body to have an adverse effect, because if they have an effect on the placenta, this will have a direct impact on the foetus," stated Dr Norrice Liu - a paediatrician and clinical research fellow, and a member of Professor Jonathan Grigg's research group at Queen Mary University of London - in her presentation.
Previous research has also indicated links between pregnant mothers' exposure to air pollution and premature birth, low birth weight, infant mortality, and childhood respiratory problems. In a 2016 study, researchers from the Johns Hopkins Bloomberg School of Public Health had said that even small amounts of air pollution appear to raise the risk of a condition in pregnant women linked to premature births and lifelong neurological and respiratory disorders in their children.
In the latest study, the researchers suggest that the black carbon particles travel from the mother's lungs to the placenta. They say further studies are needed to determine whether the particles can cross the placenta and reach the fetus.
The new research, say experts, suggests a possible mechanism of how babies could be affected by pollution while being theoretically protected in the womb. This should raise awareness amongst clinicians and the public regarding the harmful effects of air pollution in pregnant women, say researchers.
According to the researchers, additional research is required to understand whether the accumulation of black carbon particles in placental tissue may be responsible for the adverse effects associated with air pollution exposure during pregnancy.
"Our finding that black carbon particles accumulate on the fetal side of the placenta suggests that ambient particulates could be transported towards the fetus and represents a potential mechanism explaining the detrimental health effects of pollution from early life onwards. The evidence of particle translocation to the placenta might be a plausible explanation for the observed detrimental effects of ambient particulate air pollution on fetal development," says the study.