WASHINGTON (AP) — President Joe Biden saluted the nation's military veterans as "the spine of America" Thursday as he marked his first Veterans Day as president in a wreath-laying ceremony at Arlington National Cemetery.

"There's nothing low risk or low cost about war for the women and men who fight it," said Biden, whose administration earlier in the day, announced a federal effort to better understand, identify and treat medical conditions suffered by troops deployed to toxic environments.

That expanded effort centers on lung problems suffered by troops who breathe in toxins and the potential connection between rare cancers and time spent overseas breathing poor air, according to the White House. Federal officials plan to start by examining lung and breathing problems but say they will expand the effort as science identifies potential new connections.

Biden's son, Beau, served in Iraq, and the president has suggested a potential link between Beau's death from an aggressive brain cancer and his exposure to toxins in the air, particularly around massive pits where the military disposes of waste by burning. There's no scientific evidence to establish hat link.

This year's Veterans Day commemoration comes just two months after Biden ordered the withdrawal of U.S. troops from Afghanistan, a chaotic ending to America's longest war where 2,461 American service members were killed over the nearly 20-year conflict.

In his remarks at Arlington, Biden praised generations who have served, declaring they've "endured and survived challenges most Americans will never know."

He also paused to remember three high-profile veterans who recently died, Colin Powell, the former chairman of the Joint Chiefs of Staff and secretary of State; Gen. Ray Odierno, an Army chief of staff and top general in Iraq, and Sen. Max Cleland, a Georgia Democrat who lost three limbs while serving in Vietnam.

"You are the very spine of America," Biden said of the nation's veterans.

The new federal effort on toxic exposure is also designed to make it easier for veterans to make claims based on their symptoms, to collect more data from troops who are suffering and to give veterans more time to make medical claims after symptoms such as asthma and sinus problems develop.

"We're discovering there is a whole host of lung conditions related to deployment," said Dr. Richard Meehan, an immunologist and rheumatologist. The retired U.S. Naval Reserve officer, who served in the Mideast during the 1990s and again in 2008, is co-director of the Denver-based National Jewish Health Center of Excellence on Deployment-Related Lung Disease.

Beau Biden's death was a defining moment for Joe Biden, one he said affected his decision to sit out the 2016 presidential race. The younger Biden deployed from October 2008 until September 2009 as a captain in the Delaware Army National Guard. In 2013, he was diagnosed with a tumor, and he died two years later at age 46.

Meehan, who along with his colleagues is investigating the role of inhalation exposures among military personnel who were deployed to Southwest Asia, said it isn't only burn pits that are the issue — the air quality in some countries is so poor that troops would not be allowed to work there under civilian federal workplace guidelines. The center receives funding from the Department of Defense, along with private donors.

Meehan has worried that troops who came back with breathing problems are being compared with other Americans to determine whether there is a higher rate of lung illness. But those deployed with the U.S. military are in peak physical condition, stronger and more fit than average Americans. To come back unable to make it up stairs without getting winded or unable to lift anything without breathing heavily is highly unusual.

"When you compare them to another group, you have to compare them to another healthy, fit group," Meehan said. "That's one of the problems overlooked in surveys that have shown no higher incidence of cancer."

The new rules will allow veterans to make claims within 10 years of service, and the government has changed how it determines what symptoms count and why.

The U.S. military has been aware for years of health risks associated with open-air burn pits. In 2013, federal investigators found a military camp in Afghanistan was operating a pit for more than five years, nearly four times longer than Pentagon rules allowed. The Defense Department has said burn pits should be used only as a temporary last resort when no other alternative trash disposal method is feasible, still they have persisted for years.

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This story has been corrected to show that name of hospital is National Jewish 'Health' not National Jewish 'Hospital.'