Photos: Plastic by the numbers

Companies large and small are starting to turn to plastics made of plants rather than petroleum. However, most plastics are still made from fossil fuels.

Chemists have spun hundreds of kinds of plastics, but most common containers fall in one of seven categories. To help recycling centers sort landfill-bound plastics from those than can find life in new products, the Society of the Plastics Industry developed the numeric system to identify the type of plastic resins used.

One of the most common types of plastic is polyethylene terephthalate (PET or PETE), commonly found in bottles of soda, juice, water, and cough syrup, and jars of peanut butter. The bottoms of these containers are usually stamped with the chasing arrows symbol and the number 1, a code for PET.

An urban legend circulating over e-mail has warned people of cancer-causing chemicals leaching from water bottles left in hot cars, although PET is understood to be one of the least toxic forms of plastic.

The EPA no longer lists DEHA, a chemical used in PET, as a carcinogen. PET plastics do not contain softeners, found in vinyl, which studies increasingly link to cancer and infertility. Studies do show that PET bottles can leach toxic antimony, although at levels deemed safe (PDF) by the World Health Organization. Lead oxide has also been used to make PET. And doctors advise against reusing disposable plastic water bottles because they are hard to clean and can trap bacteria.