Neil_H

The simple answer to this question is yes. But the fact is that there are various kinds of plastics. Plastics may be divided into two basic groups: ones that are oil-based and ones that are plant-based.
Since plant-based plastics, such as those made from corn, can be broken down by soil organisms, they are degraded much faster than plastics made from chemicals. Bottles made from such plastics have been shown to break down in a matter of months. However, you should know that plant-based plastics degrade best when they are treated as compost and not put into landfills where they may be cut off from the action of microbes.
How fast petroleum-based plastics degrade depends on how they are made and where they are disposed of. Polystyrene (like Styrofoam) decomposes rather quickly when exposed to sunlight. On the other hand, polyvinyl chloride (Teflon ™) hardly breaks down at all.