MONTREAL -- Montreal transit workers are the latest to learn they've been wearing -- for at least six months -- some of the millions of masks distributed in Quebec that have now been identified as potentially toxic.

After Quebec issued a mass recall for the masks on Friday, following a safety warning from Health Canada, a growing pool of workers has been identified as the exposed group.

The Société de Transport de Montreal told CTV News on Monday that the masks were handed out to STM employees for months. 

A representative from the union for STM maintenance workers said distribution began sometime around September, while a worker remembered it as July or August.

It "always felt like little hairs were getting stuck in our mouths and nose," said one diesel mechanic for the STM.

He said he "started getting some rashes and more pimples around the area the mask touches," and he's not sure now if they have "something to worry about," or how to learn more.

The masks were removed from circulation on Friday, immediately after the Health Canada warning, STM spokesman Philippe Dery confirmed.

"The health of our employees is a priority, and if we had heard of something we would have been investigating, but at the time that we acquired the masks they were in compliance with the regulations," he said.

"As soon as we got the preventive recall note we reacted promptly."

The grey and blue masks are labelled as SNN200642 and are from the supplier Metallifer, which said it imported them from China and that they conformed to all regulations at the time.

In a notice Thursday, a Health Canada director wrote of "a potential emerging risk" with face masks coated with nanoform graphene materials, the layer of miniscule carbon particles that coats the masks.

Breathing in this substance presents an "unacceptable" risk of toxicity to the lungs, Health Canada said.

The next day, Quebec recalled the Metallifer masks.

Teachers and daycare workers were the first groups to learn they'd been wearing the masks, with instant recalls at schools.

The province identified these groups, as well as health-care workers, as the recipients of the problematic masks, but didn't say who in the health-care system had been wearing them.

A spokesperson for Quebec's procurement agency said they don't have a full list yet of who's affected, but they're working on it: "We're already working to identify the places that may have received the masks," he said.

Over the weekend it became clear that transit workers were also affected. But the province wasn't involved in that distribution, said the STM. 

The transit agency bought the masks itself, STM spokesperson Philippe Dery told CTV News.

"Thousands” of employees had access to the masks, he said, and those were mostly maintenance workers and mechanics -- drivers and ticket booth operators work behind plexiglass and are not required to wear masks at all.

Overall, "hundreds of thousands” of the masks have been used by STM employees over the last few months, Dery confirmed. The STM took them out of circulation on Friday, after the Health Canada notice, he said.

Dery also said that while the STM has been giving free masks out in the metro to the public, these masks weren't distributed to the public at any point.

"At no time such masks were distributed to the clients," Dery said.

"We distributed some face coverings made of cloth for the clients, [and] also some masks that are individually wrapped that are available at some ticket booth stations in the metro stations, but those masks or those face coverings are perfectly safe."

As for what led to the decision to buy these masks, it was simple at the time: the agency issued an independent call for tenders, and Metallifer had the lowest bid at $662,256.

The STM issued a call for tenders in May 2020. Other companies also supplied masks to the STM, but Metallifer was one of the agency's main suppliers.

The diesel mechanic, who didn't want his name published because of potential job repercussions, said he and his colleagues were given the masks to wear every day, 40 to 60 hours per week, since what he recalled as July or August of 2020.

The Quebec recall notice asked all establishments with the masks in question to put them in boxes in an "isolated location."

On the weekend, an education union, the CSQ, called on Quebec to enforce the matter very stricly, closing down any establishments that hadn't followed the recall to the letter.

It also demanded answers from the province on who had authorized the masks.