A young police detective who spent nearly 500 hours sifting through rubble at Ground Zero has died of a lung disease connected to his cleanup efforts, police union officials said yesterday. James Zadroga, 34, who died Thursday at his parents' New Jersey home, retired from the NYPD in July 2004 because of his deteriorating health. He is the first emergency worker to die from constant exposure to the Sept. 11 wreckage at the World Trade Center, said Michael Palladino, president of the Detectives' Endowment Association. A high-ranking police source said the department does not have the medical authority to link...