A study released Tuesday found that nearly seven out of 10 workers who responded to Ground Zero have had or are still suffering from lung problems. The Mount Sinai Medical Center study examined 16,000 workers and volunteers who assisted in rescue and recovery efforts at the World Trade Center. It's the largest study so far on health effects from the recovery work and focused mostly on the so-called "World Trade Center cough." Doctors say it is conclusive proof of a link between recovery work and long-term respiratory problems. According to the study, 61 percent of responders who had no lung symptoms before September 11th developed lung problems while working at the site. It also found that illnesses were the worst for those who arrived first.