Rescue workers and babies born to expectant mothers who were exposed to smoke, chemicals and dust from the September 11, 2001 terrorist attacks on the World Trade Center may suffer serious long-term health problems, according to a new medical study.

The collapse of New York City's Twin Towers thrust thousands of tons of construction dust, glass fibers, asbestos and lead into the air.

A new study by the National Institute of Health (NIH) found that dust from Ground Zero significantly increased cases of asthma, severe coughing and shortness of breath among firefighters and others who were close by when the World Trade Center buildings collapsed.

The report also found that pregnant women who were inside the towers or lived within a 10-block radius of the World Trade Center on September 11th were twice as likely to have low birth weight babies caused by pollutants in the air.

Dr. Stephen Levin of Mount Sinai's School of Medicine co-wrote the study. He said that those who were in or around the World Trade Center Buildings during the first 12 hours of the disaster experienced the worst effects.

"It was at that time that the amount of irritant material in the air was at its greatest," he said. "The fires were burning most intensely, the amount of dust, especially the pulverized concrete dust, that had resulted from the collapse of the towers was probably at their greatest concentration during that time. And so it is no surprise that just as with the firefighters, the most severe and most frequent respiratory problems that people developed were developed as a result of those early exposures. "

The study pointed to the potential longer-term health consequences of exposure to asbestos, a mineral fiber commonly used in building insulation. Tons of asbestos were blasted into the air when the twin towers fell.

Asbestos in the dust particles can lead to increased risk of Mesothelioma, a type of cancer, according to the report.

Dr. Levin said that cancers that are caused by asbestos may exist in the body for many years before being detected. "That's why it's so important that the population of people who had exposure to asbestos in their rescue and recovery work and in the cleanup of the surrounding buildings be followed for a long period of time," he added. "The real issue from a public health point of view is to detect these cancers at a time when you can treat them."

Some 11,000 rescue workers participated in the study. Of those who had some exposure at ground zero, 30% suffer from chronic respiratory problems and bronchial spasms. The report says that further study is needed to continue to assess the long-term effects of the World Trade Center attacks.