Analysis of the substance sent to Infrastructure Minister Denis Lebel's office in Roberval revealed it was harmless, said provincial police spokesman Richard Gagne.
There was no immediate word on the substances found in the offices of Christian Paradis, Maxime Bernier and Steven Blaney.
Gagne said three people — one each from the offices of Lebel, Paradis and Bernier — were looked at by ambulance officials but that nobody "was indisposed in any way whatsover."
He did not want to comment on certain media reports that the envelopes also contained threatening messages.
Speaking in Roberval later in the day, Lebel confirmed the envelope at his office did contain a note. Asked whether it said "Conservatives, You Will Be Annihilated," — as had been reported by other media — he replied he did not know what was written.
"We won't be intimidated and the office will be open tomorrow (Friday)," Lebel said.
The incident in Roberval, about 250 kilometres north of Quebec City, prompted authorities to quarantine two people as firefighters analyzed the scene, said Richard Cote, head of the region's emergency services.
An envelope containing white powder was later found in the riding office of Paradis, the international development minister, in Thetford Mines, south of Quebec City.
Police said a person who came into contact with the substance was transported to hospital as a precautionary measure.
The chief of staff for Bernier, the minister of state for small business, said a suspicious envelope was found in his office in Saint-Georges, south of Quebec City.
That envelope was placed in a plastic bag and handed over to provincial police without being opened after an employee saw traces of a white substance.
While nobody at the Levis office of Blaney, the public safety minister, was in contact with mail, police removed a suspicious envelope, Gagne said.
The Conservatives' only other MP in Quebec, Jacques Gourde, received no such mail, said an employee at his office near Quebec City.
Earlier, Lebel released a statement saying provincial police had taken charge of the situation and alerted the RCMP.
"These actions are taken very seriously," it read. "The safety of Canadians is a priority for our government. There can be no doubt that we will not be intimidated."
Also on HuffPost