Scientists have found the first evidence that particles of air pollution travel through the lungs of pregnant women and settle in their placentas.
Toxic air is already heavily associated with damage to fetuses, but how the damage happens is unknown. The new study, which involved mothers living in London, UK, showed sooty particles in the placentas of each of their babies, and researchers say that it is quite possible that the particles also enter the fetuses.
"It's a worrying problem – there's a massive link between the air pollution a mother breathes and the effect she has on the fetus," Dr. Lisa Miyashita from Queen Mary University in London, one of the researchers. "It's always good to take as little as possible dirty routes when you're pregnant – or even when you're not pregnant – I avoid busy roads when I go to the train station."
A number of previous studies have shown that air pollution significantly increases the risk of premature delivery and low birth weight, leading to life-long damage to health. A large study of more than 500,000 births in London released in December confirmed the connection and led doctors to say that the consequences for many millions of women in polluted cities around the world are "a public health disaster".
Scientists are increasingly finding that air pollution leads to health problems far beyond the lungs. In August, the study found that air pollution causes a "huge" reduction in intelligence, whereas in 2016, toxic nanoparticles from air pollution were detected in the human brain.
The new study examined the placentas of five non-smoking women, all of whom delivered healthy babies. The researchers isolated macrophage cells, which are part of the body's immune system and devour harmful particles such as bacteria and air pollution.
Using an optical microscope, they found 72 dark particles under 3,500 cells and then examined the shape of some particles with a powerful electron microscope. They looked very much like the sooty particles found in macrophages in the lungs, and many, but not all, of the particles.
While further analysis is needed for final confirmation, Dr. Miyashita: "We can not think of anything else they could be – it is very obvious to us that they are black soot particles." Earlier experiments have shown that particles inhaled from pregnant animals pass through the bloodstream into placentas.
"We do not know if the particles we found could also pass into the fetus, but our evidence suggests that this is indeed possible," Dr. Norrice Liu, also at Queen Mary University of London and part of the team. "We also know that the particles do not have to enter the baby's body to have a detrimental effect, because if they affect the placenta, it will directly affect the fetus."
The research will be presented on Sunday at the European Respiratory Society (ERS) International Congress in Paris. "This research suggests a possible mechanism of how infants are affected by pollution while theoretically protected in the womb," said Prof. Mina Gaga, president of ERS and Athens Chest Hospital in Greece.
"This should sensitize physicians and the public to the harmful effects of air pollution in pregnant women," she said, noting that fetal damage may even be below current European Union limits. "We need stricter cleaner air guidelines to reduce the global health impact of pollution, as we already see a new population of young adults with health problems."
Unicef's director, Anthony Lake, recently warned of the risk of air pollution for babies: "Contaminants not only harm babies' developing lungs, they can also permanently damage their developing brains and their future."
A separate study, also presented at the ERS Congress, found that children with early-onset and persistent asthma performed far less well in education than those without the disease. Asthma in children has long been associated with air pollution.
The study, conducted in Sweden for over 20 years, showed that children with asthma three and a half times more often leave school at the age of 16 with only primary education and twice as likely to drop out of university.
Dr. Christian Schyllert from the Karolinska University Hospital in Stockholm said: "This study suggests [these] Children have worse life chances when it comes to their education and their future jobs. "He said that one possible reason could be that children with asthma are known to have a low school attendance.