Plastics are used by just about every single person on earth at least once a day. Unfortunately for us that means the ingestion of some potentially deadly chemicals. For those of your wondering what is safe and what is not we're here to help. Use this guide by checking the number on the bottom of the plastic container you are using.
Number 1 - PET or PETE (polyethylene Terephthalate)
Safe and Recyclable
Number 2 (most common) - HDPE (high-density polyethylene)
Safe and Recyclable
Number 3 - Vinyl or PVC (polyvinyl chloride)
Avoid, Non-Recyclable
Number 4 - LDPE (Low-density polyethylene)
Safe and Recyclable:accepted at plastic bag recycling centers
Number 5 - PP (polypropylene)
Safe and Recyclable: check with your curbside-recycling program
Number 6 - PS (Polystyrene)
Avoid, Recyclable: check with your curbside-recycling program
Number 7 - (Miscellaneous)
PC - Questionable, not recyclable
PLA - Safe, not recyclable but compostable (made from natural products such as corn)

PLA
PLA is compostable in municiapl or commercial composts. Bags will compost in backyard composts, but containers will not as they do not have the required high heat or moisture.
As for safe for the world, PLA along with ethanol is responsible for the higher food costs and shortages according to the World Food Bank.Also the thought that it uses less fossil fuels than petroleum products is untrue. NatureWorks buys energy credits.
Please check out the article put out by Smithsonian Magazine about PLA August 2006. It's very informative as well as "How Green are Green Plastics" in Scientific American, Aug, 2000.
This corn has created a dead zone the size of New Jersey in the Gulf of Mexico due to the excessive nitrogen used. This corn is killing off insects such as the Monarch Butterfly that come in contact with them.