THURSDAY, March 31 (HealthDay News) -- While the risks of gunfire and explosive devices to U.S. soldiers stationed in Iraq are obvious, new research suggests that high levels of air pollution in that country might pose a threat to their respiratory health.

Scientists have been collecting air samples in Baghdad since 2008, and they found that the Iraqi air often contains fine particulate matter made up of many elements, including silica, sulfates and heavy metals, such as lead, arsenic, cadmium and mercury. Fine particulate matter is of greater concern than large particulate matter because these tiny particles can travel deep into the lungs, where they can cause more damage.

Some air quality readings in Iraq found that the fine particulate matter was nearly 10 times higher than the levels generally considered acceptable in the United States.

"There is concern with the amount of the fine particles in the atmosphere that the soldiers, and the Iraqi citizens, are living in," said study co-author Jennifer Bell, a doctoral student in the department of chemistry and biochemistry at the Geophysical Institute at the University of Alaska in Fairbanks.

"Fine particulate matter is very, very small. If you think about the size of a hair follicle, these particles are smaller than a hair follicle," said Bell. "The natural defenses, like the hairs in the nose, normally trap coarse particles, but these particles are so small they bypass the body's natural defenses."

What's more, she said, in a place like Iraq, where it's extremely hot, it can be very difficult to breathe that hot air through the nose, and many people breathe through their mouth. This allows fine particles to travel even further, into the deepest part of the lungs, known as the alveoli.

The alveoli are the area in the lungs that allow oxygen to pass into the bloodstream. If you've inhaled fine particulate matter into your alveoli, these particulates can pass through the alveoli into your blood, according to Dr. Hormoz Ashtyani, director of the pulmonary division at Hackensack University Medical Center in New Jersey. Once these particles are in the bloodstream, the immune system sends out cells to destroy them. But, they just get absorbed into these cells, impairing their function.

"The [immune system cells] can't rid themselves of the particulate matter and their function suffers. Resistance to infection is reduced," he explained.

These particles are also of concern because they can scar the lung tissue and affect lung function, said Ashtyani.

He said that for most healthy people, their natural defense mechanisms will overcome this exposure. Bell agreed that healthy people can generally overcome this exposure, and said that it's people who may already have a sensitivity to these fine particles, such as those with preexisting lung or heart problems, who are most at risk. However, even some healthy people may be at risk of developing a chronic cough, she added.

Bell was to present the findings Wednesday at the American Chemical Society national meeting in Anaheim, Calif.

Bell said that there are two main sources of fine particulate matter -- nature and human activity. Iraq's environment naturally has more fine particulate matter because it's desert. "There's nothing breaking up the wind in the desert. Once the wind goes, it really starts going," she said, adding that there are many natural elements contained in the sand, such as silicate minerals, carbonates, sulfates, oxides and heavy metals.

The other main source of fine particulate matter is human activity. Activities such as driving kick up a lot of dust, and gasoline containing lead hasn't yet been banned in Iraq. So, fine particles may contain additional lead.

As would be expected, fine particulate matter readings were higher during dust storms in Iraq, which happen about twice a month, and can cause winds around 60 miles per hour, according to Bell. The dust storms can last for several days.

Soldiers are given masks to help them breathe easier during these dust storms. But, Bell noted, soldiers don't always wear the masks when they should. "A lot of them don't wear them because it's so hot. It can get up to 130 degrees on some days," she said.

Ashtyani said a mask is the most effective way to protect the lungs from fine particulate matter, but he understands why soldiers might not want to wear them all the time. "If physical activity increases, a mask interferes with air movement and may cause shortness of breath. Between the heat and the discomfort, soldiers probably can't perform as much with the mask on as without it," he said.

One thing that should come out of this study, said Ashtyani, is a greater awareness of the potential problems returning soldiers may face, such as a chronic cough. He said that doctors who treat people who've served in places like Iraq and Afghanistan should be "sensitive to the subtle, and perhaps not clear-cut, complaints that these soldiers may have when they come back."

More information

Learn more about the potential health effects of particulate matter pollution from the U.S. Environmental Protection Agency.