An envelope that tested positive for the deadly poison ricin was intercepted Tuesday afternoon at the U.S. Capitol's off-site mail facility in Washington, congressional and law enforcement sources reported.
After the envelope tested positive in a first routine test, it was retested two more times, each time coming up positive, the law enforcement source said. The package was then sent to a Maryland lab for further testing.
The envelope was addressed to a U.S. Sen. Roger Wicker, according to Majority Leader Harry Reid.
Ricin is a highly toxic substance derived from castor beans. As little as 500 micrograms, an amount the size of the head of a pin, can kill an adult if inhaled or ingested. There is no specific test for exposure and no antidote once exposed.
Ricin was used in the 1978 assassination of Bulgarian dissident Georgi Markov.