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Biodegradable plastic bags. Plastic bags were previously made entirely from petroleum plastics, but poor degradability and excess environmental waste led manufacturers to use more environmentally friendly plastics. Biodegradable plastics are produced using plant-based starch, such as maize starch. These bioplastics break down much faster than petroleum plastics and can be easily composted with other household food and plant products. (KEYSTONE/SCIENCE PHOTO LIBRARY/SHEILA TERRY/SCIENCE PHOTO LIBRARY)