What is the definition of ‘biodegradable’? Here are some definitions that I found:

• capable of being decomposed by e.g. bacteria
• capable of being reduced to water and carbon dioxide by the action of microorganisms
• capable of being broken down by air, water and bacteria

Up until now, ‘biodegradable’ used to mean to me that if I throw such material into the trash, with time it will sort of dissolve into the environment without harming it. In other words, the nature would accept it back as its own.

Plant based plastic manufactured by NatureWorks is labeled as ‘biodegradable’ and is used mainly as packaging by major companies like Newman’s Own, Wild Oats and Wal-Mart. In simple terms, lactic acid is extracted from corn and then chemically processed to create strong bonding between the molecules, so it becomes polylactic acid or PLA. Currently around 20% of all plastic is PLA and it is used in the form of containers and bags.

Here is the reason why the word ‘biodegradable’ makes me think twice about how such material actually decomposes. In theory PLA is biodegradable, but only in certain conditions. I can’t say it better than what’s already been said by the experts:

“PLA is said to decompose into carbon dioxide and water in a “controlled composting environment” in fewer than 90 days. What’s a controlled composting environment? Not your backyard bin, pit or tumbling barrel. It’s a large facility where compost—essentially, plant scraps being digested by microbes into fertilizer—reaches 140 degrees for ten consecutive days. So, yes, as PLA advocates say, corn plastic is “biodegradable.” But in reality very few consumers have access to the sort of composting facilities that can make that happen. NatureWorks has identified 113 such facilities nationwide—some handle industrial food-processing waste or yard trimmings, others are college or prison operations—but only about a quarter of them accept residential foodscraps collected by municipalities.”              “Corn Plastic to the Rescue” By Elizabeth Royte, Smithsonian magazine, August 2006

These plant-based plastics will break down to basic elements and minerals, usually in an industrial composter through the activity of heat, micro-organisms and enzymes. This decomposition has to be measured by standardized tests and must take place within a specified period of time–which varies according to the ‘disposal’ method. Unfortunately, the industrial composting facilities required are so rare that only a sliver of the biodegradable plastic produced actually makes it to them. Ingeo–a polylactic acid (PLA) bioplastic developed by Nature Works–is one so-called ‘compostable’ plastic that will not break down in home composters. NatureWorks also admits that PLA will not break down if left as litter in the countryside, in soils, seawater or even in landfill. Over a much longer period of time of course it will break down, probably faster than petrol-based plastics. But there are likely PLA fragments happily bobbing around in the world’s oceans already. NatureWorks insists that PLA can be recycled, but no system is yet set up to capture and re-use PLA resin. In appearance PLA can be confused with PET (polyethylene terephthalate) used for plastic bottles and so can actually hamper recycling efforts by contaminating existing recycling streams. In October 2004, a group of recycling advocates called on NatureWorks to stop selling PLA for plastic bottles until key questions were addressed. In January 2005 the company did stop selling ‘additional’ PLA for bottle production but broke that moratorium this past April. NatureWorks has yet to test recyclability of any post-consumer PLA”. Jim Thomas, New Internationalist, September 2008

So basically, if we throw the ‘biodegradable’ bags into the trash, they won’t decompose in the landfill of garbage. At least the vast portion of them.

More facts about PLA

PLA plastic takes one and a half times as much energy to manufacture when compared to it’s counterpart, the polyenthylene or PET plastic. Therefore more fossil fuel is used for production of PLA versus PET with more emissions from the power plant. To make it easily understood, making one pound of PLA equals to the same amount of energy as burning 118 60-watt light bulbs for one hour, and only 78 bulbs for PE.

Huge amounts of corn are required to make PLA,  therefore a lot of land and fertilizer is needed to grow it. Manufacturing of fertilizer involves energy as well, since it is made from separate chemical substances into granules. Granulation process alone requires a lot of energy. These numbers are probably not being accounted for in the above PLA energy consumption number.

Some companies in UK refused to use PLA and went back to PET plastics since they believe that their country’s waste management infrastructure is not set up for handling PLA as it was meant to be handled, so mixing PLA and PE makes it more confusing for the waste management companies and the consumers.

My Contribution

I started to use reusable bags when I go shopping. Wal-Mart and Publix, the two markets that I shop at regularly, offer reusable bags for a buck or less per bag.

In case I don’t have my bags on hand, I request paper bags instead of plastic when available.

I try to buy food that requires plastic containers in bulk. For example, instead of individually wrapped single-serving yogurt containers, I buy one big container.  A lot less plastic is used for the same amount of yogurt. And it’s cheaper too!