Although many people probably aren't even aware of them, the plastic recycling codes on the bottom of bottles and containers has been generating some controversy.

The formal name is "Resin Identification Code," and it refers to the numbers from one to seven found inside the triangular arrows recycling symbol found on the bottom of plastic products like one-liter cola bottles or gallon milk jugs.Each of the numbers refers to the type of plastic resin used in the container. For instance, No. 1 refers to polyethylene terephthalate, or PET, typically used in soft drink bottles; No. 3 is polyvinyl chloride, or PVC, used in cooking oil and water bottles; No. 6 is polystyrene, typically used in food service containers and coffee cups.

The code started as a voluntary effort in 1988 to help commercial recyclers sort plastics by type. It's use has gone far beyond that, however, leading to confusion and misconceptions on the part of the public, according to a report released a month ago by the National Recycling Coalition and the Society of the Plastics Industry Inc.

The code has become mandatory in 39 states and is being used in several other countries, including Europe, Canada, Brazil, Latin America and Japan.

The problems that the recycling coalition and the plastics industry see include:

Consumers spot the recycling symbol on a container and assume that it means the container can be recycled - although it may not be recycled in their community. Community curbside recycling programs differ widely on which plastics they accept for recycling. That leads to consumers putting inappropriate plastics in a collection program, adding to processing costs.

The seven numbers aren't specific enough. Plastics differ even when the same resin is used, and sometimes they can't be melted down together for recycling. The No. 2 designation, for instance, high-density polyethylene, includes both blow-molded bottles and injection-molded containers. They cannot be melted together, but consumers may put them both in a program designed only for the bottles.