Military veterans who say they were sickened by lingering amounts of the herbicide Agent Orange aboard repurposed airplanes after the Vietnam War now have some strong scientific support for their claims.

A study published on Friday refutes the U.S. Air Force and Department of Veteran Affairs' position that any dioxin or other components of Agent Orange contaminating its fleet of C-123 cargo planes would have been "dried residues" and therefore unlikely to pose any meaningful exposure risks.

That contention has been the basis for the VA's denial of benefits to sick veterans.

"It's a question of science and ethics," said Jeanne Stellman, an Agent Orange expert at Columbia University's Mailman School of Public Health and senior author of the paper, which found standard-exceeding exposures likely occurred after the war -- via skin contact, inhalation and ingestion.

"The VA has set up policy that is based on bad science," she added. "That's resulted in really inequitable treatment."

Veterans who sprayed or handled Agent Orange herbicide during the war, or who spent any time on the ground in Vietnam, are automatically eligible for health care and disability compensation under federal Agent Orange legislation. The government presumes that certain conditions such as prostate cancer, Parkinson's disease and Type 2 diabetes are a result of exposure to the chemical.

Linda Birnbaum, director of the National Institute of Environmental Health Sciences, told The Huffington Post that, in her opinion, the VA's presumption should be expanded to include those who flew in the post-war planes.

"We can't prove it, but everything in here is supportive of the fact that they were exposed and could have been quite highly exposed," said Birnbaum. "In fact, it would be reasonable to assume that those who flew in these planes after the war were more likely to be exposed than those servicemen who had boots on the ground in Vietnam."

Perhaps no one knows better than retired Lt. Col. John Harris the consequences of the VA's apparently arbitrary distinction between possible pre- and post-war exposures.

When HuffPost first covered the concerns of Harris and other veterans last July, he described how the VA initially denied him Agent Orange-related benefits for his diabetes, despite his 12 years of working, eating and sleeping onboard what he refers to as "noxious" C-123s after the war. But when he later found records of a one-hour refueling stop he'd made with a fighter jet in Vietnam during the war, the VA granted his refiled claim.

While Harris is happy to have coverage, he remains frustrated for his comrades.

"I'm absolutely positive that I was exposed to Agent Orange and dioxin in that 12-year period," he told HuffPost after hearing about the new study. "I think the VA is lying, cheating and stealing to prove a case that is unprovable."

In a statement to the HuffPost last July, a VA spokeswoman stated that "even though residual Agent Orange may be detected in C-123 aircraft by laboratory techniques years after Agent Orange use, any residual [dioxin] in the aircraft would have solidified and be unable to enter the human body in any significant amount."

VA spokeswoman Genevieve Billia told HuffPost in email on Friday that the agency "wants to ensure that all Veterans, including those who served on C123s, receive the benefits to which they are entitled under the law," and that it will "continue to review new scientific information on this issue as it becomes available."

"VA does not presume by regulation that these Veterans were exposed to Agent Orange," said Billia.

To show that such exposures likely did happen, Stellman said, her research team had to be "very clever."

After a decade of spraying more than 10 million gallons of Agent Orange to destroy enemy cover and crops, the C-123s underwent no testing -- or decontamination, for that matter -- prior to their new stateside assignments with the Air Force Reserve. Between 1971 and 1982, about 1,500 men and women served aboard 34 C-123s that were previously deployed in Operation Ranch Hand.

It wasn't until 1979, when crews complained about chemical smells, that officials took the first measures of potential contamination. Samples of wiped surfaces in 1994, and again in 2009, supplemented this 1979 air sample data. All but three of the planes have since been smelted.

Stellman, Richard Clapp of the Boston University School of Public Health, Fred Berman of Oregon Health and Science University and Peter Lurker, an environmental engineering consultant and former U.S. Air Force researcher, used this sparse data in three different models. All resulted in estimated exposure levels that exceeded health guidelines for the contaminants.

The team noted that their findings may be extremely conservative.

The levels of toxic chemicals -- measured years, even decades, after the veterans were aboard the C-123s -- were likely much higher immediately after the war, researchers said. Airborne levels may also have been particularly high while the planes were airborne, due to extreme temperatures, changes in pressure and vibrations.

One of the models that researchers used, which Stellman suggested was based on a "high school chemistry" concept, demonstrated how the old herbicide could have evaporated and attached to dust particles.

"The VA, whether out of ignorance or malice, has denied the entire existence of this entire branch of science," said Stellman. "They have this preposterous idea that somehow there is this other kind of state of matter -- a dried residue that is completely inert."

Clapp, one of the co-authors, emphasized how "exquisitely toxic" dioxin is at any dose. The chemical has been linked to a host of health effects including cancers, heart disease and diabetes.

"Exposure to even tiny quantities is not ignorable," he said.

"We do show plausible exposure," added Clapp. "These veterans should be compensated, too."

Retired Maj. Wes Carter, who himself served aboard C-123s after Vietnam, has been leading the effort on behalf of this group of post-war veterans. He said he knows of only one such comrade who has received Agent Orange benefits from the VA, his close friend retired Lt. Col. Paul Bailey.

Bailey was among those struggling to secure benefits for himself and his family last July, when he was gravely ill with cancer. He died of the disease in October.

Bailey expressed his frustrations to HuffPost back in July.

"We've proved over and over that we've been exposed to dioxin, but the VA is refusing to accept the evidence," said Bailey, who worked as an air medical technician and flight instructor aboard the C-123s. "They're just dragging their feet."

Weeks before Bailey's death, the VA reversed its initial denial of his claim.