A white powder found in Senate Majority Leader Bill Frist's office tested Tuesday as an "active" form of the deadly poison ricin, forcing cancellation of most Senate business in the second such scare from a lethal toxin to hit the capital.
Officials have found no evidence that anyone was significantly exposed to the poison enough "to make them sick, said Dr. John Eisold, the Capitol physician however, he urged employees to be alert for symptoms over the next 48 to 72 hours.
Nebraska Senators Chuck Hagel and Ben Nelson were temporarily displaced from their offices Tuesday after the discovery of the powder.
Sixteen people were on the floor of the Dirksen Senate Office Building where the white powder was discovered on mail. Police say they were being decontaminated and were allowed to go home.
The discovery, however, also prompted closure of all Senate buildings Tuesday. That includes the Russell office building -- where Hagel has his offices -- and the Hart building -- where Nelson has his offices.
Frist said that tests confirmed that the powder was ricin: "It is active, how active we don't know." He said he was confident that everyone who was at risk has been identified.
U.S. Capitol police chief Terrance Gainer said everything that was in the 4th floor mailroom in Frist's Dirksen Senate Office Building office has been seized, but that authorities have not yet analyzed all of the mail.
Senator Tom Daschle, the Democratic leader, likened the events to the 2001 incident in which his office received letters containing potentially deadly anthrax.
"Terrorists acts, criminal attacks of this kind, will not stop the work of the Senate or the Congress," Daschle said at a briefing.
"We remain vigilant," he said. "People should err on the caution side. If there is a question they should see us."