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Wild Green

Former Utne Reader senior editor Keith Goetzman on environmental issues from climate change to composting.


‘Compostable’ Plastic Claims Break Down

 by Keith Goetzman


Tags: Environment, green living, sustainable business, composting, plastic, biodedegradable, bioplastics, compostable plastics, plastic bags, Mother Earth News, Terrain, Keith Goetzman,

Bioplastics chart“Compostable” plastics are being marketed as a green solution to waste and pollution—but our sister magazine Mother Earth News found in an independent test of “bioplastic” bags that many of them don’t live up to their claims. Of five bags tested, none of them were completely compostable in home composting conditions.

Mother Earth News commissioned the test from Woods End Laboratories, which specializes in evaluating composts, soils, and organic wastes. The lab found that some of the bags did break down under high under higher temperatures resembling commercial composting operations—but this is seldom spelled out in marketing claims. Writes editor Cheryl Long:

The bottom line: Most plastic packaging that claims to be “biodegradable” or “compostable” will only partially break down under the conditions typical of most home compost piles.

Check out the full bioplastic bag report online (pdf) and look for an article about it in the June-July issue of Mother Earth News, which goes on sale May 25.

Even though some bioplastics can break down in larger operations, cities that are pioneering municipal composting programs have had problems with the materials, reports the Northern California environmental magazine Terrain. In October 2009, a group touring Berkeley, California’s municipal food and yard waste composting site

... observed employees picking all plastic items—both petroleum– and plant-based—out of the dumped materials. Any smaller plastics that made it through the initial screening were removed later, as the material was sent through a trommel and a sorting station.

Here’s the reason: even if bioplastic items are suited to break down in a commercial facility, they look nearly identical to the petroleum-based plastic they are meant to replace, which makes it difficult for workers at the plant to distinguish between the two. Because of the quantity of waste they are sorting, and the difficulty of identifying the types of plastics that arrive at the facility, laborers remove all plastics, including most compostable bioplastics, which are then hauled off to the landfill along with the other contaminants.

Source: Mother Earth News, Terrain