"DANANG, Vietnam (AP) ??? The United States began a landmark project Thursday to clean up a dangerous chemical left from the defoliant Agent Orange ??? 50 years after American planes first sprayed it on Vietnam's jungles to destroy enemy cover.Dioxin, which has been linked to cancer, birth defects and other disabilities, will be removed from the site of a former U.S. air base in Danang in central V" . . . .