A new corn-based plastic disappears into the dirt

When you next buy a tub of potato salad, the container it comes in may be made from another vegetable - corn.

A new line of corn-based plastics, called polylactides or PLA, has begun to land on supermarket shelves. Its strongest selling points are that it fully degrades in 47 days, doesn't emit toxic fumes when incinerated, and requires 20 to 50 percent less fossil fuel to manufacture than regular plastics.

In May, 11 Wild Oats Markets on the West Coast became the first grocery stores in North America to switch from conventional plastics to the new corn-based product, with plans to roll them out nationally into all 90 stores later this year.

As part of the roll-out, Wild Oats has installed in-store bins where customers can return their empty containers. "We then take them to an industrial composting facility and they turn the containers into compost, which we then sell in our stores to people who buy it for their gardens," says Sonja Tuitele, communications director of Wild Oats.

A European retailer has also been selling the new plastic products. IPER, a 21-store chain in Italy, has been using the packaging for a year and has expanded its use from deli departments to dairy and bakery areas.

The new plastic has a few quirks, however. The biodegradable materials won't break down in regular landfills; they have to be taken to special industrial sites and treated like compost. Nor will they decompose in home compost bins: Temperatures there don't reach the required 284 degrees F. Yet the containers will melt if filled with hot food, or placed in the dishwasher or microwave.

Cargill, an international agriculture corporation, and Dow Chemical, have a joint venture making one line of PLA. Within 10 years, says Cargill spokesman Michael O'Brian, the company expects to be making 1 billion pounds of corn-derived plastics each year. That would mean 10 percent of the nation's annual corn supply would be converted into plastics and fiber.

PLA can also be used as an alternative for molded foam products, electronic packaging, and cups. For instance, the Coca-Cola Company used 500,000 cups made from corn at the 2002 Olympic Winter Games in Salt Lake City. And instead of creating a huge trash problem, the used cups were composted and turned into dirt.

What separates biodegradable plastics from their more long-lived cousins are polymers. Plastics based on natural plant polymers, derived from wheat or corn starches, have molecules that are easily broken down by microbes; traditional plastics have polymer molecules too large and too tightly bonded together to be broken apart by decomposer organisms.

Most biodegradable plastics currently on the market are between two and 10 times more expensive than traditional plastics. Yet plastics constitute 9 percent of the 156 million tons of trash Americans generate each year, and many consumers would be willing to pay the extra costs for a replacement product that biodegrades. According to a recent survey from market research firm RoperASW, 51 percent of respondents would pay a premium of up to 10 percent for environmentally safer versions of plastic packaging.