Montreal implemented its long-planned ban on plastic bags on Monday, making it the first major Canadian city to do so. The ban covers the distribution of lightweight plastic bags with a thickness of less than 50 microns as well as biodegradable bags, which contain an additive that causes them to decompose in heat and light. …”We use roughly 2 billion of these bags annually and only 14 per cent are reintegrated in recycling plants,” said Jean-Francois Parenteau, the city council member responsible for the environment. …Thicker plastic bags, paper bags and cardboard boxes will also be allowed.