Officer Tom Waterman spent weeks amid the smoldering rubble of the World Trade Center, assisting with the recovery and cleanup after the September 11th attacks. 

He remembers the air being thick with dust and chemicals. 

"I don't know how to describe it. Gray, you know," Waterman said.

Waterman felt fine during the years that followed. But in January, his health took a terrifying turn. He was diagnosed with stage three esophageal cancer that doctors believe could be the result of contact with toxins unleashed by the towers' collapse.

"It's pretty scary," Waterman said.

More than 2,600 people died when hijackers flew two planes into the Trade Center, and the Twin Towers came down.

Since then, a second tragedy has been unfolding, in slow motion: A growing number of 9/11 first responders and survivors falling ill and dying from diseases that could be caused by contact with the poisonous dust and air, which contained asbestos, benzene, PCBs, and more than 400 chemicals.

"We had a witches brew. It was mix like no other," said Dr. Michael Crane, Medical Director at Mount Sinai's World Trade Center Health Program.

The federal World Trade Center Health Program says the number of first responders and survivors who are enrolled for monitoring or treatment has climbed to more than 89,000.

More than 10,000 of them have cancer. Most of those who have fallen ill were first responders. 

"It's crazy. Guys are dropping," Waterman said.

The toll at the police department is startling. At least 156 NYPD members have died from illnesses that could be linked to 9/11.

That's more than six times the 23 officers who died on that day. 

The fire department lost 343 members on 9/11. 

But the number of FDNY deaths that could be caused by 9/11 toxins keeps climbing - 17 members this year alone, 182 overall - more than a hundred of them from cancer.

"What constantly surprises me is that we're seeing these cancers at an earlier time than we would have expected," said Dr. David Prezant, Chief FDNY Medical Officer.

According to a recent study, the risk of developing cancer among 9/11 first responders is up to 30 percent higher than the general public.

Researchers say more studies are needed to conclusively prove a link between the toxins and the illnesses. Experts expect the deaths will keep climbing but they are unsure how many there will ultimately be.

"We're certainly in the water. That's for sure. I think iceberg is going to emerge. I don't know when, though," Crane added.

Tom Waterman was not in that program prior to this year. Now, he's recovering from radiation and chemotherapy and surgery that removed part of his stomach and esophagus. 

"I lost a lot of strength. Hopefully everything will return, and I'll get back to normal," Waterman said.

Waterman continues to go for treatments, and says he prays his cancer does not come back.