How biodegradable are biodegradable plastics?

Illuminating answers to environmental questions.
May 12 2009 11:31 AM

Breaking Down Is Hard To Do

How biodegradable are biodegradable plastics?

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Do biodegradable products really break down in landfills?

My fraternity is about to throw a massive party to celebrate the end of finals. Every year, we wind up with trash bags full of Dixie cups, so we've been considering greening up our debauchery by switching to biodegradable ones. What are our options?

You could always switch to uncoated cups made from a natural fiber like bagasse, which comes from sugar cane pulp. These can be reliably biodegraded in a compost pile, if your frat house or university has one. The only problem is, you'd need to shred all those cups into small pieces to make sure they broke down properly—an unlikely scenario, unless you have a bunch of recruits who need some hazing.

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These days, you can also find a number of plastic products—not just cups but also plates, bowls, and straws—that trumpet their biodegradability. But because the federal government doesn't regulate "biodegradable" as a marketing term (as it does for, say, "organic"), manufacturers can sometimes get away with being a little squirrely in their advertising. In fact, none of these products will magically disappear wherever you happen to toss them. Not all biodegradable cups break down at the same rate, or to the same extent, or in the same environment. (The Federal Trade Commission can take action after the fact when environmental claims aren't backed up by "competent and reliable scientific evidence," but it doesn't pre-approve labeling.)

The best means we have to assess biodegradable products is by subjecting them to the standard tests of the American Society for Testing and Materials—an independent organization that has established various methods for measuring how plastics decompose in different environments, including soil, oceans, active landfills, and industrial composters. If you're really, really dedicated, you might call up a cup manufacturer and ask if it has lab results from ASTM biodegradability tests or comparable tests from the International Standards Organization or the European Committee for Standardization.

Even these would be of limited use for most consumers, though. There's not much reason to be concerned about what happens when your empties end up in the soil (since you know better than to litter, right?) or the ocean (unless you're planning a booze cruise). The more important question is what happens in the landfill, where most of the disposable party paraphernalia ends up. But the corresponding ASTM data assume conditions in a "biologically active" landfill—one in which, say, the liquid that oozes out of the garbage pilegets recirculated to make the trash moist and hospitable to hungry microbes. In fact, modern landfills are generally designed to keep garbage as inert as possible, to reduce greenhouse gas emissions and the amount of potentially toxic liquids that might seep out and contaminate groundwater. Trash is compacted tightly and covered daily with dirt and clay to reduce odor. While this approach may have some environmental benefits, it tends to retard the breakdown of virtually all biodegradables—even vegetable scraps. In a famous series of landfill excavations that began in the 1970s, University of Arizona "garbologist" William Rathje uncovered five-year-old heads of lettuce that were still in good condition.

Then there's the fact that biodegradability may not be a worthy goal in the first place! The tomblike conditions in most landfills mean that any biodegradation that occurs is going to be anaerobic. In the absence of oxygen, the process produces methane, a greenhouse gas that's 21 times more effective at trapping heat than carbon dioxide. So your biodegradable party-ware might end up warming the planet more than a standard plastic cup—which would at least sequester its carbon for a long, long time.

All of this means that, if you want to go with a biodegradable product, you have to do your homework. Look for plastic cups that make clear, precise disclosures about where and how they should be disposed of and the amount of biodegradation that can reasonably be expected. To be sure of yourself, get cups that have been certified as compostable by the Biodegradable Products Institute and the U.S. Composting Council—they'll be marked with a circular tree-and-leaf logo. But these aren't a perfect solution to the waste problem either, since they're only guaranteed to biodegrade in a professionally managed composting facility. (You can use findacomposter.com to find the one closest to you.) Keep in mind that if you have to make a special trip to dump your cups, the exhaust from your car might negate all your good intentions.

If all that sounds complicated, that's because it is. The bottom line is that disposable cups are never going to be any good for the environment, and until there's a better infrastructure for properly collecting and composting them, it's not clear whether using the biodegradable versions will help very much at all. For your party, then, the Lantern suggests reusable beer steins, or, better yet, the trusty keg stand—no cups required.

Is there an environmental quandary that's been keeping you up at night? Send it to ask.the.lantern@gmail.com, and check this space every Tuesday.

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