Now that San Francisco’s supervisors have banned plastic bags in supermarkets, the city is looking to prohibit the use of plastic bags to keep newspapers from getting soaked by rain. The Chronicle reports today that Supervisor Ross Mirkarimi wants to ban the use of plastic newspaper bags unless they’re biodegradable. Biodegradable bags are also more expensive. Mirkarimi said that in the coming months, he will study how many plastic bags are generated by newspapers, restaurants and other sources to determine their impact on the environment. He could not say when legislation on those bags might be introduced.