"The study included 12,781 workers...[and] notes that the event exposed the workers – as well as those living and working in the surrounding area – to a dense cloud of pulverized building materials and chemical byproducts, including pulverized glass and cement, insulation fibers including asbestos, and toxic chemicals."

http://www.mymeso.org/2010/04/08/study-reveals-persistent-significant-reduction-in-lung-function-for-911-responders-workers/

A study published today in The New England Journal of Medicine reveals that Fire Department of New York (FDNY) firefighters and emergency medical services (EMS) workers who responded to the 9/11 attacks at the World Trade Center have suffered significant, persistent declines in lung functions. According to the report, exposure to World Trade Center dust created when the towers collapsed led to “large declines” in lung functions for FDNY rescue workers during the first year, and that “the declines were persistent, without recovery over the next 6 years, leaving a substantial proportion of workers with abnormal lung function.”