Bioplastics offer chance to cut use of petroleum

CAMBRIDGE - Target offers shoppers an unusual message about its gift cards at some stores, advising that they are biodegradable. "Just make sure you spend them first," the displays conclude.

Plastics made from corn and other plants are are being touted as green alternatives for everything from bulk food containers to lipstick tubes and clothing fiber, as well as gift cards.

But their makers' green argument is complex, and environmentalists are cautious in their support. Manufacturing bioplastics produces carbon dioxide, which contributes to global warming. The materials are made from crops that require land and water to grow. Some sound alarms because genetically modified organisms are used to spur the fermentation that creates them. They also can cost three times more than conventional plastics, which gives businesses pause.

Bioplastics' main benefit would be to reduce the share of US petroleum consumption that goes into plastic, from its current 10 percent. The types that are biodegradable could help compensate for the country's slow progress in recycling; only about 6 percent of plastic made in the United States was recycled in 2005, says the US Environmental Protection Agency.

Bioplastics also lack toxins like polyvinyl chloride that have raised health concerns and led Governor Arnold Schwarzenegger of California to sign legislation this month banning chemicals called phthalates from toys and baby products.

The market's newest entrant is Mirel, from Cambridge-based Metabolix Inc. It more easily biodegrades than rival materials and, unlike others, can break down in a backyard compost bin. In July, Target Corp. began using it in gift cards at 129 stores. Metabolix is talking with potential clients about dozens more applications for Mirel, from razor blade handles to a coating for disposable coffee cups.

Agricultural processor Archer Daniels Midland Co. provides corn feedstock for making Mirel, which requires genetically engineered bacteria to aid in fermentation.

The most widely used bioplastic, NatureWorks - a product of a subsidiary of Minnesota-based Cargill Inc. - also is corn-based and biodegradable. It is made without genetically modified bacteria.