GWEN IFILL: Brain injury and post-traumatic stress disorder are two well-known signature wounds of the wars in Iraq and Afghanistan. But there is another injury, lung disease, that afflicts tens of thousands of veterans. Many blame a single defense contractor and have filed a class action lawsuit, a case that has now made its way to the Supreme Court.

NewsHour producer Dan Sagalyn has been covering this, and Hari Sreenivasan has the story.

MAN: We have a burn pit down here.

HARI SREENIVASAN: This shaky video of smoke from burning garbage was shot by an American soldier in Iraq in 2008. Throughout most of the wars in Iraq and Afghanistan, the military used so-called burn pits to dispose of virtually all waste.

MAN: That is what we leave next to. Luckily, the wind is not blowing our way today.

HARI SREENIVASAN: All kinds of things went up in smoke, from batteries, paint, solvents and tires, to newspapers, plastic water bottles, styrofoam, electronic equipment, and shipping materials such as plastic wrap. Even whole vehicles were burned.

At large bases, 30 to 40 of tons garbage were burned every day. At the gigantic logistical hubs, three to five times that amount was burned. Sometimes, jet fuel was even used to ignite the trash. According to the veterans we spoke to, the smoke from the burn pits permeated the living quarters and work spaces on base.

SGT. 1ST CLASS STEVEN GARDNER, (RET), U.S. Army: There was really no place to escape. The smoke would blow across you, you would turn your back to it, and hope that the wind would change.

LT. COL. RICK LAMBERTH, (RET.), U.S. Army: You have to breath, or you die. And, sometimes, even the soot would fly out of the burn pits and get on your uniform or on your vehicle.

LT. COL. BRIAN BOWER (RET.), U.S. Marine Corps: At night, when the winds dropped, that's when you didn't want to the burn pits to be operating because it would blanket the base.

HARI SREENIVASAN: These three officers, Army Sergeant 1st Class Steven Gardner, Army Lieutenant Colonel Rick Lamberth, and Marine Corps Lieutenant Colonel Brian Bower, were medically retired from the military. They say the burn pit smoke was toxic and made them sick.

SGT. 1ST CLASS STEVEN GARDNER: I used to run five-minute miles. Now I can't walk down the block without breathing real heavy. I can't carry objects without getting out of breath. I have a tightness constantly in my chest.

LT. COL. RICK LAMBERTH: I no longer can hold out to run. I don't have the stamina. At one time, I could go run five or 6.6 miles at a time, a 10k at a time.

A lot of times even during the day, I cough and people look at me like I'm a smoker. Sometimes it's embarrassing.

LT. COL. BRIAN BOWER: I believe that I have lung cancer as a result of exposure to the burn pits. I'm not a smoker. I was diagnosed within a year after leaving active duty. And the diagnosis came from the Veterans Administration. It was diagnosed as exposure to burn pits, and I had part of my lung removed.

HARI SREENIVASAN: These men are part of a class action lawsuit which has 250 named plaintiffs. But they represent a group of potentially up to 100,000 veterans and civilian contractors who could join suit.

They're suing Kellogg Brown & Root, or KBR, the company that used to be a subsidiary of Halliburton and was contracted to provide logistical support to the military in Iraq and Afghanistan. It was KBR's job to truck in supplies, feed troops, and get rid of the garbage.

SUSAN BURKE, Lead Attorney: We have outlawed burning of waste in this country for decades. You cannot go in your backyard and burn all your trash in a bucket. And the reason why is that it's known to be harmful to human health.

HARI SREENIVASAN: Susan Burke is the lead attorney for the class action lawsuit. She says KBR was negligent and made the service members sick.

SUSAN BURKE: One of the things that they promised to do was to take care of the waste, to dispose of the waste in a manner that wasn't harmful to the troops. They didn't do that. So, the complaint alleges that that open air burning, which violated the terms of the contract, caused these injuries.

ROBERT MATTHEWS, Attorney, KBR: That's completely false. We exactly lived up to our contractual promise.

HARI SREENIVASAN: Robert Matthews is the lead counsel for KBR. He points to a letter from the commander of coalition forces in Iraq, General David Petraeus, to Congress written in 2008.

The letter says — quote — "There is and will continue to be a need for burn pits during contingency operations."

The Government Accountability Office issued a report confirming that the top military commanders approved the use of these open air fires.

ROBERT MATTHEWS: The decisions to use burn pits were made by senior military rank across these war theaters.

HARI SREENIVASAN: Matthews says other alternatives were not feasible. Burying the refuse off base was too risky. Burying it on base, well, there wasn't enough space. There was no recycling in Iraq and Afghanistan. And it was up to the military to decide if it wanted to bring in incinerators which burn cleanly. He says historically the Army always burned its garbage in war zones because it's the least bad option.

ROBERT MATTHEWS: More than 50 percent of the burn pits that are in play around Iraq and Afghanistan through that 10-year period were operated by the military itself, not by KBR or other contractors.

HARI SREENIVASAN: The class action lawsuit has been in the courts since 2008. Just earlier this year, the Fourth Circuit Court of Appeals ruled the case should go forward. But KBR has asked the Supreme Court to intervene. The company asserts that, just like the government, it should be immune from lawsuits.

ROBERT MATTHEWS: Where the United States is at war on a battlefield engaged in combatant activities, the companies like KBR who are embedded with the forces, who are performing mission-critical services shouldn't be subject to the kind of claims that have been made here. If the United States is immune from such claims, so too should KBR and those other contractor companies.

HARI SREENIVASAN: Susan Burke disagrees.

SUSAN BURKE: What they're trying to say is that simply because they work for the government, they are the government. We know that's not the case. This is a private company that's making a huge profit margin. They are not the government and they don't deserve the government immunities.

HARI SREENIVASAN: By 2010, the military eventually shipped in nearly 40 incinerators to Iraq and 20 to Afghanistan, although the veterans we spoke to said they often were not used.

MAN: We don't know if we're receiving fire, but that's exploding paint cans.

HARI SREENIVASAN: Besides these legal issues, there is debate over how much burn pits contributed to people's illnesses.

Craig Postlewaite is a top official in the Defense Department's Public Health Division. He says it's possible some soldiers got sick from inhaling burn pit smoke, but not likely that many were affected.

CRAIG POSTLEWAITE, Department of Defense: It would be plausible for a specific individual maybe to acquire some kind of condition related to burn pit smoke depending on how close they were to the burn pit, how much smoke they breathed, individual susceptibilities and even exposure to other airborne particulates. We feel that if there are people who have been harmed by burn pit emissions, the numbers are fairly low.

HARI SREENIVASAN: Postlewaite points to many other pollutants in the air that could have caused veterans' respiratory problems.

CRAIG POSTLEWAITE: It's a very, very dusty environment. Plus, the urban pollutants aren't regulated well. The cars and trucks are not regulated, so there's a lot of airborne material in the air that could be contributory towards long-term health effects.

HARI SREENIVASAN: But Dr. Anthony Szema sees a direct connection between sick veterans and the burn pits. At Stony Brook School of Medicine in New York, where he does research, he's exposed mice to dust from military bases in Iraq that had burn pits.

DR. ANTHONY SZEMA, Stony Brook School of Medicine: And this healthy mouse, we then gave dust from Camp Victory Iraq collected in 2007 at the time they had burn pits, and the dust induces a lung injury.

HARI SREENIVASAN: Szema has a private practice and is also a doctor at Northport Veterans Affairs Medical Center, although the views he expresses here are his own.

DR. ANTHONY SZEMA: Humans exposed to particulate matter air pollution have a higher risk of death, premature death. They have higher risks of lung disease such as premature emphysema, chronic obstructive pulmonary disease, even in the absence of smoking, as well as asthma. Benzene is a carcinogen, so if you burn your trash with jet fuel called JP-8, when you burn in a burn pit, it's burning at low heat. At low heat, it generates more particles and has products of incomplete combustion.

These products are dangerous. In addition, if you burn plastic water bottles, among the chemicals you can release include a neurotoxin called n-Hexane.

HARI SREENIVASAN: While the lawyers and the health professionals debate the legal and medical issues, the veterans we spoke to compare their experiences to soldiers exposed to Agent Orange in Vietnam. That's the defoliant the Army used which caused cancer, nerve damage and respiratory injury in hundreds of thousands of soldiers.

Marine Corps Lieutenant Colonel Brian Bower:

LT. COL. BRIAN BOWER: Nobody went out to purposefully hurt, again, soldiers, airmen, sailors and Marines. And so — but people are suffering from exposure to it afterwards. And the military response is very similar probably to Agent Orange, which was at first denial, assessment, acceptance of culpability, and treatment. We seem to be going through those same phases now.

HARI SREENIVASAN: The veterans we spoke to say while they wish they weren't sick, they'd still serve in Iraq and Afghanistan all over again.

SGT. 1ST CLASS STEVEN GARDNER: I'm proud of my military service. I'm proud of what the military has done over there. If I had known that this would be my outcome, I still would have continued and done exactly the same thing.

HARI SREENIVASAN: Meanwhile, KBR says if they and other battlefield defense contractors are allowed to be sued, it's unlikely they would deploy with the military in the next war.

ROBERT MATTHEWS: If they are exposed to these lawsuits for decades of litigation and potentially tens, if not hundreds of millions of dollars in liabilities, then it's very likely that these companies are going to think twice about stepping forward the next time this country goes to war.

HARI SREENIVASAN: The Supreme Court is now in the process of deciding whether or not to hear this case or send it back to a lower court, where it can go to trial.

For the "PBS NewsHour," I'm Hari Sreenivasan.

JUDY WOODRUFF: If you would like more on this story, go to our Web site for extended interviews and a slide show of burn pit photos submitted to us by those who served in Iraq and Afghanistan.