According to the Associated Press, a source said an envelope addressed to the White House contained the poison Ricin.
According to the Mayo Clinic, Ricin is a poison that is made from the waste left over from processing castor beans. Castor beans are used to make oil.
According to the Mayo Clinic, Ricin can potentially be used as a biological weapon. The poison can be turned into an aerosol or put into food or water.
