Ten years after two jets crashed into the World Trade Center in the Sept. 11 attacks, scientists are still learning about the long-term health effects of the disaster.

Researchers led by a team from the Mount Sinai School of Medicine in New York City have reported anew that physical and mental illnesses were very common across a large group of 9/11 emergency responders — and remained persistent for 10 percent to 30 percent of them a full nine years after the disaster.

The study, which followed 27,449 emergency workers, was released recently by the journal Lancet.

More than 50,000 people are believed to have worked in rescue, recovery and cleanup operations at the World Trade Center site. The workers, which included police officers, firefighters, construction workers and municipal workers, were exposed to toxic smoke generated by burning jet fuel, and a thick cloud of dangerous dust — a pulverized mix of glass fibers, asbestos, lead and other dangerous particles and chemicals — produced when the towers collapsed. The workers were also placed under intense stress. The research team divided the volunteers who participated in the study into four groups, based on their exposure to the site and its debris. Eighty-six percent were men, 57 percent were white and their median age on the day of the attacks was 38.

Over the nine years the scientists studied, 27.6 percent of the subjects were diagnosed with asthma (compared with a baseline before 9/11 of 10.5 percent), 42.3 percent with sinusitis (baseline 10.7 percent) and 39.3 percent with gastroesophageal reflux disease (baseline 5.8 percent).

Among rescue and recovery workers, 27.5 percent had been diagnosed with depression (versus a 3 percent baseline) and 31.9 percent had been diagnosed with post-traumatic stress disorder (versus a 1 percent baseline). The authors reported that police officers were at lower risk for mental illness than other responders, perhaps because their training and experience better equipped them for dealing with traumatic situations.

Workers with the greatest exposure at ground zero had the highest incidence of multiple disorders. Almost 10 percent of the rescue and recovery workers had asthma, sinusitis and gastroesophageal reflux disease; 18 percent had two out of the three ailments. Sixty-nine percent of rescue workers with post-traumatic stress disorder had a physical condition as well, as did 70 percent of those with depression and 72 percent of those with panic disorder.

"We now know that, in one of the largest WTC rescue and recovery cohorts, health effects have persisted for almost a decade," wrote Matthew P. Mauer of the New York State Department of Health, in an accompanying editorial.

"These latest findings leave no doubt about the necessity of continuing health monitoring, treatment and research for WTC rescue and recovery workers ... (and) emphasize the critical importance of including the study of long-term health effects in any future disaster response plan."