Public safety responders found a 2-year-old girl unconscious in Roxbury Tuesday afternoon, authorities said. Boston police, fire, and Emergency Medical Services workers responding to a report of a cardiac arrest at 1833 Washington St. at 4:41 p.m. found the girl unresponsive, said Officer David Estrada, a police spokesman. EMS took the girl, whose identity was not released, to Boston Medical Center, where she was treated for a life-threatening condition, Estrada said. It was not immediately clear what happened to the child or if foul play is suspected. No other details were available Tuesday night.Nicholas Jacques can be reached at email@example.com.