Plastic is synthetic and pretty new, very few bacteria have the ability to biodegrade the plastic polymers into smaller molecules. There are at least one known bacteria that is able to break down the plastic, but this is not normally found in the places we tend to throw away our plastic.Trash Travels estimates that plastic bags can take 20 years to decompose, plastic bottles up to 450 years, and fishing line, 600 years; but in fact, no one really knows how long plastics will remain in the ocean. With exposure to UV rays and the ocean environment, plastic breaks down into smaller and smaller fragments.