Additive Accelerates Decomposition

`WE really think this can change the world,'' says Martin Andreas, senior vice-president of Archer Daniels Midland, an agricultural products manufacturer in Decatur, Ill. ``Polyclean'' is ADM's proprietary additive that makes plastics both chemically and biologically degradable. It has two components: a natural metal salt that acts without air, water, or light on carbon molecules in the polymer chain, breaking them into smaller and smaller pieces; and cornstarch, which can be consumed by microbes in the soil. The additive is being used by several companies across the United States and in Canada, where St. Lawrence Starch of Toronto has a patent on a similar additive.

So far the application is available only in plastic film, like that used in grocery bags. If enough is added to constitute 15 percent of the plastic, the bag should break down into small bits within six months to two years, depending on conditions. Within five years the residue will be completely gone, says Mr. Andreas - into carbon dioxide, water, and humic matter.

A regular plastic bag, he says, will take three to five centuries to degrade in a closed landfill.

But Rebecca Falkenberry, professor of international and urban environmental issues at the University of Alabama in Birmingham, isn't convinced that cornstarch should be used to make products degradable. First, she notes, corn is harsh on non-renewable topsoil, stripping it of nutrients and promoting erosion.

Second is the issue of world food supply. Says Ms. Falkenberry, ``We have to ask ourselves, `Is that the best use for food products?'''