Funding for the World Trade Center Health Program expired at midnight on Wednesday, leaving tens of thousands of its beneficiaries, who have health problems resulting from exposure to toxic chemicals at Ground Zero, wondering how they will continue their medical treatment.

The program was created as part of the James L. Zadroga 9/11 Health and Compensation Act of 2010 (PDF) to offer medical care to the survivors of the Sept. 11, 2001 attacks as well as first responders who worked at the site. More than 72,000 people have enrolled in the $4.2 billion fund.

To the dismay of those enrolled, Congress failed to approve an extension of the Zadroga Act. The law was named after James Zadroga, the first New York City police officer to die as a result of 9/11’s aftermath, from what medical examiners said were chemicals he was exposed to during the hundreds of hours he spent helping with rescue and recovery operations.

Zadroga was one of more than 1,700 people who died as a result of health conditions that are believed have been caused by toxic chemicals, including asbestos, lead and glass fibers, at the former WTC site. First responders and others who spent time in the area have contracted many kinds of unexplained illnesses. Often, they were respiratory in nature — from asthma and acid reflux disease to chronic obstructive pulmonary disease and a condition that became known as World Trade Center cough.

For many of the WTC Health Program's beneficiaries, their illnesses did not become apparent until years after their first exposure. More than 3,600 new members joined the program in the last year, according to the Centers for Disease Control and Prevention.

Without the program, many will lose health coverage. “Stress is not even the word. It’s beyond stress,” Nick Polisano, 37, a first responder who has sarcoidosis, a respiratory condition involving abnormal cell growth in the lungs, told The New York Daily News. He spends four entire days every month receiving treatment at the Robert Wood Johnson University Hospital in New Brunswick, N.J., one of seven treatment centers for first responders set up by the program.

The newspaper said Polisano’s treatments will end when funding runs out. “My life depends on this,” he said.

The program has enough funding for another year, but CDC director Tom Frieden has said that in 2016 it will face “significant operational challenges” without an extension.

Rep. Carolyn Maloney, a Democrat from New York, introduced a new version of the bill last spring that would permanently reauthorize the Zadroga Act, but Congress hasn’t passed it yet.

“If Congress doesn’t act now, how many more first responders and their families are going to suffer — medically and financially — because we didn’t do our job and reauthorize this program?” Sen. Kirsten Gillibrand, D-New York, said in a speech to her fellow senators on Tuesday. She added that more police officers have died in the aftermath of 9/11 than did in the attacks themselves.

New York City Mayor Bill De Blasio urged Congress on Wednesday to pass an extension for the program and blasted lawmakers for “putting politics ahead of our heroes’ health.”

“That is unacceptable,” he said in a release. “Our first responders were there for us on 9/11 and every day after—and we have a moral obligation to be there for them.”