Two tests were done to confirm the presence of ricin. All mail for the White House is sorted and screened at an offsite facility before reaching the White House.
A US law enforcement official told CNN that investigators are looking into the possibility the ricin package sent to Trump came from Canada.
Mary-Liz Power, chief spokeswoman for Canada's Minister of Public Safety Bill Blair, said in a statement, "We are aware of the concerning reports of packages containing ricin directed toward US federal government sites. Canadian law enforcement is working closely with their US counterparts. As this is an active investigation we cannot comment further."
The FBI and Secret Service are investigating the matter.
Authorities are investigating additional similar packages mailed to addresses in Texas that may be connected to the same sender in Canada, a US law enforcement official said.
Ricin is a highly toxic compound extracted from castor beans that has been used in terror plots. It can be used in powder, pellet, mist or acid form. If ingested, it causes nausea, vomiting and internal bleeding of the stomach and intestines, followed by failure of the liver, spleen and kidneys, and death by collapse of the circulatory system.
"The FBI and our U.S. Secret Service and U.S. Postal Inspection Service partners are investigating a suspicious letter received at a U.S. government mail facility. At this time, there is no known threat to public safety," the FBI's Washington field office said in a statement to CNN.
CNN has reached out to the Secret Service for comment.
This story has been updated with further developments.