Bags labeled “biodegradable” and “compostable” are available in 3, 13, and 96-gallon sizes from Amazon, product manufacturers, and your local grocery store. There are small to large compostable bags for everything from kitchen trash to leaf bags, even small pick-up bags to tidy up after your dog. Advertising on the packages claim that these bags degrade like apples or autumn leaves and disintegrate in landfills. But are these claims true? And are you really doing the earth a favor when you spend twice the money for a “green” bag? Well, maybe yes; maybe no.
Undefined Terms – What Is Biodegradable? Or Compostable?
Poly bags touted as “biodegradable” are petro plastic bags contain additives that cause the plastic to become brittle and then break into pieces. When exposed to air and light, these pieces get smaller and smaller until they cannot be seen. Did they biodegrade or is this a case of out-of-sight-out-of-mind? Are the bits becoming plastic dust, waiting for an opportunity to enter the food chain at a microbial level? Frankly, no one has studied the consequences of degraded poly bags and come up with a definitive answer.
The State of California has decided that the term “biodegradable” is essentially meaningless. On October 8, 2012, Governor Jerry Brown signed a bill that prohibits the sale of plastic bags labeled with the term “’biodegradable,’ ‘degradable,’ or ‘decomposable,’ or any form of those terms.” Furthermore, “…while scientific technical standards exist to verify that a product is ‘compostable,’ there are no such standards to verify if a product is ‘biodegradable’ because the conditions and timeframe inherent in the claim of ‘biodegradability’ are too vague.”
Compostable bags (American Society for Testing and Materials – ASTM D6400) are primarily made of small amounts of biodegradable polyester resins (made from petroleum products) added to renewable resources such as vegetation starch. It’s complicated, but suffice it to say that a bag made from corn is not all corn or it would not “hold together” as a useful film. Scientists have made a lot of progress developing these “bioglues” – biodegradable plasticizers – that give bioplastics the flexibility, stability and durability of petro plastics.
Low Demand, High Cost
Right now the demand for compostable bags is small; around one percent of plastic bag orders. Because these bags are niche products, biofilm resins are expensive and bag manufacturing is limited. This drives up the price of compostable bags. Economics 101 and bag manufacturers say that prices will fall as demand increases. But does this mean that we should use more compostable bags to boost production and lower cost? Would this have a positive effect on the environment? Again, it’s complicated.
At this point, the starch component in compostable bags is primarily corn, potatoes, beets, tapioca, or other food crops. Aren’t those things we should be eating…or distilling? Agriculture requires water, fertilizer and fossil fuels for cultivation. Companies are working on ways to manufacture bioplastics using biomass (such as switchgrass and corn stalks), algae, bacteria, and solid waste. But as with Marty McFly’s hoverboard, we’re not there yet.
“Green” Bags with No Place To Go
The biggest barrier to widespread use of compostable bags is lack of infrastructure for collecting and recycling organic waste. A 2013 study by Columbia University showed that the U.S. generated a total of 389 million tons of municipal solid waste (1.3 short tons per capita). Although food waste and yard trimmings make up 28% of this waste, only 6.3% is composted.
Many communities collect recyclables, including paper, plastic, cans and glass in bins separate from trash receptacles. But very few provide well-promoted organics recycling programs with distinct collection bins and lists of acceptable materials. Unless you do yard composting, you probably rely on an infrastructure that streams organics directly to local landfills.
Compostable bag manufacturers who don’t keep their fingers crossed behind their backs always disclose on the package that the product only fully degrades at a commercial composting facility. If the bag escapes into the natural world, it will trash up the landscape and come apart slowly or very, very slowly depending on climate. In a yard compost pile, it will come apart slowly or very, very slowly depending on climate and your due diligence. In a septic tank or other anaerobic digestor, it will degrade so slowly it will muck up the works. If the bag is sealed in a landfill without water, air, and robust microorganisms, it won’t degrade for centuries. And as it degrades, it will yield methane gas.
Recyclers complain bitterly when compostable bags are mixed with incoming plastic bags. A single compostable bag can contaminate a whole batch of petro plastic material. So if customers are careless with disposal, these bags can cause more trouble than they’re worth, eco-wise.
All of this begs the question: What’s the point of using compostable bags unless the material inside them is headed directly to a commercial composting facility? And the answer, of course, is that there is no point. The best you can do is re-use plastic bags or buy bags made of recycled plastic. Or go a step further and support public policies to develop a community composting infrastructure that will meet the challenge of sustainability.
Sources:
- Plastic: A Toxic Love Story, Chapter 8 “The Meaning of Green,” Susan Freinkel, Houghton Mifflin Harcourt, 2011
- State of Composting in the U.S., BioCycle, July 2014
- Calculating Tons to Composting in the U.S., BioCycle, February 2015
- Guides for the Use of Environmental Marketing Claims, IV Compostable – Federal Register
- SB-567 Recycling: plastic products – California Legislative Information
