The campaign headquarters of Democratic presidential candidate John Edwards reopened Thursday after authorities determined the white substance found in an envelope wasn't dangerous, campaign officials said.

"The test results of the white powdery substance received (Wednesday) have come back negative, and the authorities have informed us that it is safe to return to the office," Jonathan Prince, deputy campaign manager, said in a written statement.

The Chapel Hill, N.C., office was evacuated Wednesday after a campaign worker opened a legal-sized envelop containing the powder. The woman was interviewed by health officials and has shown no health problems, Chapel Hill police spokeswoman Jane Cousins said.

The worker tossed the envelope in a bin that contained other mail, Cousins said.

Police contacted the regional hazardous materials response team, the FBI and the fire department. The response team tested the mail bin for radiation and chemicals, then determined it was safe to transport it to a state health lab in Raleigh for testing.

Edwards, a former North Carolina senator who lives in Chapel Hill, was scheduled to be in New Hampshire on Thursday.

White powder found in letters has been associated with anthrax since five people died and 17 were sickened by the substance in 2001. Anthrax was mailed to lawmakers on Capitol Hill and members of the news media in New York and Florida just weeks after the Sept. 11, 2001, terrorist attacks.