By David Shukman
BBC News science correspondent
The number of people with medical problems linked to the 9/11 attacks on New York has risen to at least 15,000.
The figure, put together for the BBC, counts those receiving treatment for problems related to breathing in dust.
Many of the victims say the government offered false reassurances that the Manhattan air was safe and are now pursuing a class-action lawsuit.
On Tuesday, a coroner said the death of a policeman who developed a respiratory disease was "directly linked" to 9/11.
James Zadroga - who worked at Ground Zero - died in January. The New Jersey coroner's ruling was the first of its kind.
Jeff Endean used to be the macho leader of a police Swat firearms team. Now, he has trouble breathing and survives on the cocktail of drugs he takes every day.
Kelly Colangelo, an IT specialist, used to have good health but now endures a range of problems including allergies and sinus pain.
"It worried me that I've been damaging my health just being in my home," she told the BBC News website. "It also worries me that I see the health impact on the [the emergency crews at the scene]. We were also exposed and I wonder if in 10-15 years from now, am I going to be another victim?"
Both are victims of what used to be called "World Trade Center cough", an innocuous sounding condition that many thought would pass once the dust that rose from the attacks of 9/11 had blown away.
But the medical problems have not merely intensified; the list of victims has grown alarmingly at the same time.
The apparent cause? The long line of contaminants carried by the dust into the lungs of many of those at, or near, the scene on that fateful day.
One list of sufferers has been compiled at the Mount Sinai Medical Center. Its World Trade Center Screening Programme has 16,000 people on its books, of whom about half - 8,000 - require treatment.
A further 7,000 firefighters are recorded as having a wide range of medical problems, producing a total of 15,000. But the overall numbers affected could easily be far higher.
Workers were allowed back into lower Manhattan soon afterwards
As the US government's newly appointed "health czar" John Howard confirmed to the BBC, there were between 30,000 and 50,000 people at or near Ground Zero who might have been exposed to the hazardous dust and no one really knows how many are suffering problems now.
Consisting of billions of microscopic particles, the dust was especially toxic because of its contents.
A grim list includes lead from 50,000 computers, asbestos from the twin towers' structures and dangerously high levels of alkalinity from the concrete.
Many of the people now suffering were sent to Ground Zero to help search for survivors. Others volunteered. Still more just happened to be living or working in the area.
The latter feel particularly aggrieved, even betrayed.
In the days following the attacks, the head of the US Environmental Protection Agency (EPA) declared that monitoring operations had proved the "air was safe to breathe". And with that reassurance, the authorities reopened the globally important financial hub of Wall Street.
At the time it was seen as a critical morale-booster to a wounded nation.
However, in the months and years that have followed, community groups, the labour movement and local politicians have fought to raise awareness of the hazards and to lift the profile of the problem.
Now the federal courts have allowed a class-action lawsuit to be filed against those very authorities.
Last month, a judge described the EPA's reassurances as "misleading" and "shocking the conscience". The legal process could last years.
A special report on the dust fallout from the 9/11 attacks will be featured on BBC World starting on Wednesday 3 May at 1930 GMT. The documentary will also be carried on BBC News 24.