It turns out that air pollution is worse on us than we may have previously known, especially for those not yet born. According to the findings of a new study, pollution can be so pervasive that it can penetrate a pregnant woman's placenta and may threaten the health of a developing fetus.

The study reviewed and analyzed high-resolution images taken of placenta tissue retrieved from 28 women who had given birth at East-Limburg Hospital in Genk, Belgium. Of these, five gave birth prematurely. The remainder carried their babies to term. In either case, placenta tissue was retrieved within 10 minutes after each child's delivery.

The research team found black carbon particles produced by fossil fuel combustion in the placenta of all the participating mothers. The mothers studied who were living in relatively polluted areas showed much higher levels of carbon particulates in the placenta than those from less polluted areas.

This first-of-its-kind study shows that pollution particles can reach the fetal side of the placenta, said study author Hannelore Bove, a postdoctoral researcher with the Centre for Environmental Sciences and Biomedical Research Institute at Hasselt University in Diepenbeek, Belgium.

Whether those particles harm fetal development is not yet clear, but one might think any outside environmental pollutant entering a woman's placenta is not a good thing.

The study set out to determine whether pollution was present in the placenta. What’s the takeaway? That the placenta is not entirely protected from the outside world.

“This matches previous findings and proves that more than was previously thought can cross the placenta," said Bove.

In the 1960s, the so-called thalidomide crisis first showed us this, she said. The sleeping pill drug's ingredients were in the placenta in pregnant women, triggering birth defects.

Since then, other substances, including alcohol, drugs and now fossil fuel pollution, were found to cross over. "Black carbon particles are thought to be especially toxic since they can absorb toxic compounds like heavy metals and benzene," said Bove.

These cancer-causing agents can mix with the oxygen and nutrients that feed a developing fetus.

What can be done to avoid pollution? Not much, researchers said.

However, air pollution’s impacts don’t stop there. In a separate, unrelated study by researchers from Monash University in Australia, exposure to toxic air pollutants showed a link to increased cardiovascular and respiratory death rates.

The study, led by Dr. Haidong Kan from Fudan University in China, analyzed air pollution and mortality data collected from 652 cities in 24 countries and found increases in total deaths linked to exposure to inhalable particles and fine particles.

Published in the New England Journal of Medicine, the international study investigated the short-term impacts of air pollution on death, conducted over 30 years.

Associate Professor Yuming Guo from Monash University's School of Public Health and Preventive Medicine in Australia said there's no threshold between particulate matter and mortality, but that even low levels of air pollution can increase the risk of death.

"The adverse health effects of short-term exposure to air pollution have been well documented, and known to raise public health concerns of its toxicity and widespread exposure," Professor Guo said. "The smaller the airborne particles, the more easily they can penetrate deep into the lungs and absorb more toxic components causing death."