Preliminary tests on suspicious white powder in two envelopes discovered Wednesday at the Portland International Airport and a downtown Portland Hilton Hotel have come back negative for toxic substances, according to emergency officials.

Beth Anne Steele, an FBI spokeswoman, said the substances have been transported to the Oregon State Public Health Lab for additional analysis. The source of the two envelopes, as well as others found in a Lloyd Center Mall mailroom on Tuesday and the Mark O. Hatfield Federal Courthouse on April 26, is still under investigation, she added.

An envelope with suspicious white powder was reported found in the Port of Portland Headquarters Building around 5 p.m. The building was evacuated and no airline service was affected, said Port of Portland spokesman Josh Thomas.

Another letter with suspicious white powder was discovered at the Hilton Hotel on Southwest 6th Avenue a little before 5:30 p.m., said Portland Police Spokesman Lt. Robert King.

He said some people were isolated because of possible contamination concerns. The area deemed cleared around 7:30 p.m.

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