Since returning home from Iraq and Afghanistan, an untold number of soldiers have come down with puzzling health problems. Chronic bronchitis. Neurological defects. Even cancer. Many of them are pointing the finger at a single culprit: The open-air "burn pits" that incinerated trash – from human waste to computer parts – on military bases overseas.

Pentagon officials have consistently reassured personnel that there was no "specific evidence" connecting the two. But now, only days after Danger Room uncovered a memo suggesting that Army officials knew how dangerous the pits were, an animal study is offering up new scientific evidence that links burn pits to depleted immune systems.

"The dust doesn't only appear to cause lung inflammation," says Dr. Anthony Szema, an assistant professor at Stony Brook School of Medicine who specializes in pulmonology and allergies, and the researcher who led this latest study. "It also destroys the body's own T-cells." Those cells are at the core of the body's immune system, "like a bulletproof vest against illnesses," Szema tells Danger Room. When they're depleted, an individual is much more prone to myriad conditions.

For scientists, trying to establish a definitive connection between those diffuse health problems and the pits has been exceedingly difficult to do. Most notably because the Department of Defense, as a report issued by the Institutes of Medicine noted last year, didn't collect adequate evidence – like what the pits burned and which soldiers were exposed – for researchers to draw any meaningful conclusions about the impact of the open-air incinerators. Szema's study is only on 15 mice, so it's by no means definitive. But it is an important first step.

Regardless, it's becoming increasingly clear that Pentagon officials were aware of the risk posed by the pits. Another memo (.pdf), written by Lt. Col. Darrin Curtis in 2006 and obtained by Danger Room, warned of "an acute health hazard" to personnel stationed at Iraq's Balad air base. "It is amazing," he noted, "that the burn pit has been able to operate ... without significant engineering controls being put in place."

But as recently as yesterday, when asked about the leaked Army memo obtained by Danger Room (which cited a risk of "long-term adverse health conditions" from the pits), Pentagon spokesperson George Little told reporters that "we do not have specific evidence that ties these kinds of disposal facilities to health issues."

Perhaps not. But researchers just got way, way closer. A team, led by Dr. Szema at Stony Brook University, this week revealed to Danger Room the results of their ongoing investigations that are trying to directly link health problems to the air emitted by burn pits. And the results should cause those who served near the pits – which burned trash at most major bases in Iraq and Afghanistan during at least some period over the last decade – to be concerned.

Dr. Szema's team used dust samples taken from around the burn pits at Camp Victory, Iraq (provided to them by the Army Corps of Engineers). That environs, according to Army Officer Daniel Tijerina (who blames the pits for his own chronic health problems), was rife with the fumes of incinerated "animal carcasses, asbestos insulation ... lithium batteries, paints and paint strippers ... copiers, printers, monitors, glues [and] styrofoam," among other equipment, waste and chemical products.

The dust from Camp Victory was inserted into the airways of mice, and researchers tracked their subjects' responses using two metrics: A pathologist examined tissue samples from the lungs for signs of inflammation, and the team used flow cytometry to count the T-cells in each subject's spleen. The researchers found that the mice exhibited lung inflammation and suppressed immune cell counts within a period of two hours after exposure. More specifically, their T-cell counts dropped by one-third. Two weeks later, their T-cell counts had plummeted again, leaving the mice with 30 percent of the T-cells they'd had before the dust exposure.

All of the mice also exhibited inflammation in their airways, often alongside interstitial inflammation – swelling in the tissue network that extends throughout the lungs and facilitates the exchange of gas and air between the lungs and blood.

"I can't even imagine what this data shows when you think about someone coming back from Iraq," Szema says. "These guys weren't inhaling this air once. They were working in it, sleeping in it, exercising in it. For days and days on end."

Although Dr. Szema's research relied on animal models, he says he's confident the results "are highly applicable when you consider a human case." They certainly seem to match the symptoms popping up among thousands of soldiers, many of whom have logged their ailments on a database at BurnPits360, a website dedicated to the topic. And his findings regarding immune-system suppression might help explain why soldiers exposed to the same fumes are now afflicted with vastly different illnesses.

This study is also the first to examine current exposure and the onset of symptoms. Earlier research has been less comprehensive. The IOM study, for example, simply studied a host of air samples taken from Iraq. Other, epidemiological, investigations have evaluated the current health metrics of soldiers who'd served near the burn pits. None have actually tested the air samples on living subjects and then tracked the results.

Certainly, the research adds more heft to that earlier work. But even Dr. Szema, who is also conducting an analysis that uses the BurnPits360 database to compare soldier symptoms with their likely exposures, acknowledges that his results shouldn't exactly be surprising. "Based on the patients I've seen, this is a no-brainer," he says. "If anyone tries to say, 'Oh, dust is just dust,' I can tell them that's simply not true."