Mexico City is Western Hemisphere 's second large metro area to ban the bags . Comment: The bag wasn't banned because it caused a problem, but rather because of how people used them and what they did with them. U.N. agency : Plastic bags are second-most common form of litter . Bags a major threat to ocean wildlife , U.N. agency says .
Mexico City is Western Hemisphere 's second large metro area to ban the bags . Move comes as leading environmentalists call for global ban . U.N. agency : Plastic bags are second-most common form of litter . Bags a major threat to ocean wildlife , U.N. agency says .