Anthony Hardie spent years arguing that American troops who fought in the Persian Gulf in 1991 suffered from exposure to toxic chemicals.

Now, he is suffering from a bout of déjà vu.

The U.S. military says that more than 600 American service members, who served in Iraq after the 2003 invasion, have reported possible exposure to chemical agents abandoned by the Iraqi military — remnants of the arsenal Saddam Hussein unleashed against Iranian troops and his rebellious Kurdish population in the 1980s.

"The DOD has a terrible track record of troops exposed to chemicals in the 1991 Gulf War and clearly the same thing again from 2003 forward," Hardie told VICE News.

Iraq's chemical weapons consisted largely of mustard gas — a weapon used with horrific consequences in World War I — and the nerve gas sarin.

Lt. Col. Matthew Clark, who co-wrote an Army medical text on the long-term effects of chemical warfare, said any health problems Iraq veterans may face will depend on what kind of agent they were exposed to and in what quantity.

"If it's a low-level exposure, it's probably not going to have any sort of enduring effect," said Clark, who teaches at West Point, the U.S. military academy. But he added: "The literature on that is fairly unclear with regard to what the impacts are."

Matthew Meselson, a Harvard University biologist and chemical weapons expert, said veterans who say they were exposed to chemical weapons should be checked by a dermatologist for burns, by an ophthalmologist for eye damage, and by a neurologist to test for nerve damage. Mustard gas burns the skin, eyes and lungs, and scars left by exposure to it are likely to still be visible, he told VICE News.

"If it was mustard — and the Iraqis had used mustard against the Iranians — there would be blisters," Meselson said. "But if they've been cured and they don't have any eyesight problem, it's passed away."

'Having people call into a phone number and tell somebody behind a desk that they were exposed to something, that's not effective.'

If exposure to a nerve agent was limited, he told VICE News, "recovery should be essentially complete."

The United States invaded Iraq in 2003 after accusing Baghdad of harboring a secret, ongoing chemical weapons program, along with biological weapons stockpiles, and making efforts to produce a nuclear bomb. No active weapons programs were found, though an American-led survey reported in 2004 that it had found "a small number of old, abandoned chemical munitions."

Those munitions were scattered across a country littered with old weapons, some of which were soon turned against U.S. troops by opposition Iraqis. In at least two cases in 2004, Iraqi fighters, who aren't believed to have known what they contained, used chemical shells as roadside bombs against American forces.

In October, The New York Times reported that the number of abandoned shells and bombs found scattered across Iraq topped 5,000 — and that at least 17 American veterans had been hurt by their exposure to them. It reported Thursday that the number had risen to more than two-dozen and that the Pentagon was looking into more than 600 other reports of exposure to chemical weapons.

Army Medical Command spokeswoman Maria Tolleson told VICE News that 629 troops potentially were exposed to chemicals in Iraq. The Pentagon has set up a toll-free number — 1-800-497-6261 — for veterans to call if they worry that they, too, were exposed and it's stepping up efforts to find others, she said.

The veterans already identified by the Times will be interviewed and may get medical exams, Tolleson said, adding that the military will reach out to troops from the same units as service members who report their exposures.

Hardie served on an advisory committee that found evidence of chronic, persistent illnesses in U.S. troops who served in that conflict. He told VICE News the Pentagon's announcement was "a nice step in the right direction."

But, he added, the Defense Department had reached out to veterans of the 1991 conflict in a similar fashion, then "meticulously, one after another, denied all these claims."

"I don't have confidence yet," he told VICE News.

He said veterans should be offered the chance to come into a military or Veterans Affairs hospital to be tested, "and if they actually test positive and get treatment, that's how we'll know."

"Having people call into a phone number and tell somebody behind a desk that they were exposed to something, that's not effective," Hardie told VICE News.