Air Carrier Captain reported a passenger had an unknown white powder fall from overhead binds on to the passenger's hair. Medical service determined passenger unfit to fly resulting in removal from flight.

Narrative

Prior to cabin door closure a passenger stated white powder fell from an overhead bin onto her hair and demanded that the powder be tested for safety. Flight Attendants requested cleaners remove the powder. Cleaners removed visible powder from the overhead bin. Flight Attendant reported the incident to the Captain and stated the passenger took photos of Flight Attendant and her name tag. Captain requested GSC (Ground Security Coordinator) board the aircraft. Dispatch was contacted and Chief Pilot) directed flight crew to notify GSC to request the Hazmat Team handle the disposition of the white powder. GSC stated there is no Hazmat Team at ZZZ. Passenger expressed concern for her safety; but refused to move to another seat and refused assessment from EMTs. CS (Customer Service) offered passenger the option to take another flight and passenger declined. CS Manager contacted medical services; which determined the passenger was not fit to fly. CS Manager escorted passenger off of the aircraft.