People exposed to the terror and dust of the 2001 attacks on the World Trade Center have higher rates of asthma and post-traumatic stress than those who were further away from Ground Zero. But they also have high rates of a less obvious health problem: heartburn.A new study of more than 37,000 adults who worked at Ground Zero or lived near the site found that one-fifth experienced heartburn, indigestion, or acid reflux for the first time ever in the three years following the 9/11 attacks.