Air pollution particles inhaled by pregnant mothers can make their way into the tissues and organs of developing fetuses, according to a new study. Although the health consequences are not yet known, the findings are sparking concern that ambient air pollution from things like burning fossil fuels and vehicle emissions can affect fetuses before they even leave the womb.
Previous studies had found evidence of “black carbon” particles in the placenta, but for the first time researchers showed that these particles could cross the placenta and enter the fetal circulation system, eventually ending up in a fetus's organs.
Black carbon particles were detected in the maternal blood, cord blood, placenta, and first and second trimester fetal tissues, including the liver, lungs and brain, the study authors wrote.
The groundbreaking findings from researchers at the University of Aberdeen in Scotland and Hasselt University in Belgium were published in The Lancet Planetary Health.
Black carbon or soot particles are produced by incomplete combustion from things like fossil fuel engines, coal-fired power plants, incineration and wood-burning stoves, according to Paul Fowler, Ph.D., chair in translational medical sciences at the University of Aberdeen in Scotland. "Lack of environmental controls on emissions can (also) affect and contribute to air pollution," Fowler added.
These tiny nanoparticles accumulate and, along with others, create "particulate air pollution," according to the study authors.
When the polluted air is inhaled, the nanoparticles enter the lungs and become absorbed into the bloodstream, said Fowler, who co-led the study. “We know that these actual particles can be taken up by cells. … Basically the cell forms a little pocket and takes the particle on board in a process called phagocytosis,” said Fowler.
These black carbon particles are also coated with chemicals, metal, or organic pollutants, said Fowler. “If these particles are getting into the cells, they will carry those molecules into the cell, as well … so you’re getting double exposure to the particles themselves and the chemicals that are stuck on the particles,” Fowler added.
Inhaling black carbon particles has been associated with a number of health problems, including respiratory disease, cardiovascular disease, cancer, and birth defects, according to the U.S. Environmental Protection Agency.
“It’s pretty well established that (maternal) exposure to high levels of air pollution are associated with a lot of adverse outcomes, both for the mother and for the pregnancy,” said Fowler. These include a higher risk of a miscarriage, potential cognitive defects, and lower birth weight, he added.
How did the study work?
The findings of the new study may help explain the developmental impairments that have been observed after exposure to particulate air pollution. Previous research had shown the presence of black carbon particles in placenta, said Fowler, but it was unclear whether these particles could enter the fetus or its organs during gestation.
“We had the possibility of (using) a technique to visualize these black carbon particles, first in the placenta, and ... we really wanted to know whether they can reach the fetus,” said Tim Nawrot, Sc.D., professor of environmental epidemiology at Hasselt University in Belgium and study co-author.
The study included cohorts from two independent studies: 60 mother-newborn pairs from the ENVIRONAGE (ENVIRonmental Influences ON AGEing in Early Life) study in Belgium and 36 fetuses from the SAFeR (Scottish Advanced Fetal Research) in Scotland. (Cigarette smoke is a source of black carbon particles, so the study only included non-smoking mothers.)
A team of researchers led by Nawrot in Belgium observed the levels of black carbon particles using samples of maternal blood, placenta, and umbilical cord blood taken immediately after birth from the mothers and newborn infants, said Fowler. Researchers found evidence of the black carbon particles in the cord blood, which confirms that these particles are able to "cross the placenta and enter the fetal circulation system,” the study authors wrote.
“They found the levels were highest in the mother’s blood, and they were still pretty high in the cord blood and the placenta, but proportionately so,” said Fowler, adding that, at this stage in the research, it was still unclear whether the fetus was protected. “The placenta does a lot of protecting, but it’s not an impermeable barrier by any means."
This is where Fowler’s team came in. Researchers in Scotland studied 36 normally progressing, electively terminated fetuses with a gestational age of 7 to 20 weeks, according to the study. These included samples from the fetuses' placenta, lungs, liver and brain. “We found that every single tissue section and every single organ from every single fetus had black carbon deposits in it, quite similar in levels to those we saw in the placenta,” said Fowler.
Researchers found a “considerable number of particles,” or around 6,000 per cubic millimeter, said Nawrot. “Now, we have proof of direct exposure before the child even leaves the womb and breathes in air pollution."
These findings are “especially concerning” because this window of exposure during the first and second trimester is “key to organ development,” the study authors wrote. “This is a very susceptible period,” said Nawrot.
Fowler said that “what’s even more worrying" is that the fetal brain had black carbon deposits, meaning it's directly exposed to not only the black carbon particles but also the chemicals they are coated in.
What are the health effects?
Further research is needed to understand whether "translocation of the particles into the fetus and black carbon accumulation in fetal organs could be directly responsible for observed adverse health effects during early life," the study authors wrote.
“There is lab evidence that these particles can affect cell death, can affect immune cells, and can affect the mitochondria of cells. … If this is happening in human fetuses, that may well contribute to explaining the adverse consequences that we see associated with air pollution,” said Fowler. "It's worrying, but have we proved that it’s definitely the cause? No."
Another important takeaway is that neither Scotland nor Belgium have particularly poor air quality or high concentrations of black carbon particles, said Nawrot. “It’s just very normal values for Western Europe, (or) quite low concentrations, and even then, these particles still end up in fetuses."
What, if anything, can expecting mothers do?
There aren’t many individual actions to combat ambient air pollution, the experts noted. However, people can ensure they are not adding to air pollution in their homes by not using wood-burning stoves, said Fowler.
More particles accumulate in the air close to major roads, Nawrot noted, so avoiding those is another option. “The particles are so teeny that even masks will not sufficiently prevent inhaling them,” he added.
It's a problem that requires government-level action, said Fowler. “This is absolutely not the time to talk about cutting air-quality regulations,” said Fowler. “Air pollution ... doesn’t sit on the border, waiting for its passport to be stamped. It goes where the wind takes it, so this is an international issue.”