Exposure to severe air pollution can cause birth defects and even fatalities during pregnancy, new research has found.

According to the World Health Organization, nine out of 10 people worldwide breathe air containing a high level of pollutants, and one of every 9 global deaths can be attributed to exposure to air pollution, totalling over 7 million premature deaths a year. The research, published in the journal Proceedings of the National Academy of Sciences, showed definitive proof of decreased fetal survival rates, and also shortened gestation rates that can result in smaller body weight, in addition to damage to brains, hearts and other organs in the adult rat models.

The research team used female rats and examined the adverse health effects of exposure to fine particulate matter consisting of ammonium sulfate commonly found in many locations around the world. During winter months in India and China, where severe haze occurs frequently, fine particulate matter levels were especially high at several hundred micrograms per cubic meter, said the researchers.

"People typically believe that ammonium sulfate may not be terribly toxic, but our results show large impacts on female pregnant rats," said Renyi Zhang, Professor at Texas A&M University in the US.

"It is unclear yet what is causing these profound effects, but we speculate that the size of nanoparticles or even the acidity may be the culprit," Zhang said.

Sulfate is mainly produced from coal burning, which is a major energy source for much of the world in both developed and developing countries. Ammonium is derived from ammonia, which is produced from agricultural, automobile and animal emissions. "So this certainly represents a major problem worldwide," Zhang added.