The SNN200642 masks, which are made in China and sold and distributed by a Quebec-based company called Métallifer, had been part of Canada's public school reopening plan.

Students were told that they needed to wear them in the classroom to prevent the spread of the Wuhan coronavirus (Covid-19).

Health Canada, however, discovered during a preliminary risk assessment that the masks contain microscopic graphene particles that, when inhaled, could cause severe lung damage.

"Graphene is a strong, very thin material that is used in fabrication, but it can be harmful to lungs when inhaled and can cause long-term health problems," reported CBC News.