Police spokeswoman Jane Cousins said the packages, which were delivered through the mail, were two of 10 suspicious packages reported to the department since Oct. 11.
Cousins said the department sends all suspicious materials to the health department only after human contact is made with the questionable substance.
The first sample tested was received by a Chapel Hill man Oct. 12.
Upon opening the envelope containing the mysterious powder, the man immediately called 911. He sealed the envelope and its contents in a plastic bag.
A similar envelope was received at the Triangle Women's Health Center on Oct. 15. Local police officials treated the substance as a biohazard material before sending it to a laboratory for testing.
A third envelope was received Oct. 15 by Chapel Hill's Planned Parenthood office, a reproductive health and family planning center.
But Cousins said the substance was not tested because no one was exposed and Chapel Hill police policy was followed.
Paige Johnson, Planned Parenthood's director of public affairs, said the clinic was adequately prepared to handle the situation due to warnings received from its other facilities nationwide. "Over 100 (envelopes) were sent to affiliates throughout the country," Johnson said. "But everything has turned out to be negative."
She said the envelopes had return addresses of either the U.S. Marshals or the Secret Service, and were marked "Urgent." The envelope sent to the Chapel Hill Planned Parenthood clinic was similarly marked, and employees, who recognized it as suspicious, called 911.