The long-term effects of the 9/11 attacks aren’t merely existential. Whether the collapse of the Twin Towers and exposure to the stew of dust and chemicals caused disease, and the emotional toll it took on witnesses, are scientific questions, too.

New estimates suggest that of the more than 400,000 people who were directly exposed to the strikes, 35,000- to- 70,000 developed post-traumatic stress disorder (PTSD), and 9,700-to-2,000 people experienced serious psychological distress. Some 3,800 to 12,600 people may have developed asthma, New York City epidemiologists report in this month's Journal of Urban Health.

Most of those people who developed asthma did so in the year following the attacks, but some may not have shown symptoms until as long as three years later, Deputy Health Commissioner Lorna Thorpe told the Associated Press. The city's newly published data from its World Trade Center Health Registry documents diagnoses within the first three years after 9/11; the estimates are based on surveys of more than 71,000 Ground Zero rescue and clean-up workers, residents, students and downtown building occupants.

Notable is the 3 percent incidence of new adult asthma cases since the attacks, which is two-to-four times higher than estimates of new adult cases nationally, scientists write in the study. The rate of PTSD symptoms among registrants is magnified by the same degree over national rates from various traumas.

How long will the trauma of 9/11 last? Victims of previous catastrophes such as the Holocaust, genocides in Cambodia and Rwanda and the 1995 bombing of the federal building in Oklahoma have shown trauma symptoms years or decades later.

But seven years later, controversy still swirls around  a link between exposure to the Pile and illnesses such as sarcoidosis that some rescue and recovery workers developed later.

Proving a connection between the environmental exposures and cancers, respiratory and digestive diseases remains a dicey — and highly political — proposition, doctors who are treating workers and city residents have found. A lung biopsy of the first of those workers to have his name added to the official list of those killed by 9/11 (James Zadroga) found no trace of World Trade Center dust, according to a piece in this week’s New Yorker. A lawyer for Zadroga's family told the New York Times that the police detective would still be alive if not for 9/11.

(Image from Joel Meyerowitz/Bureau of Educational and Cultural Affairs)