Biodegradable Plastic Bags Shouldn’t Be Confused With Compostable Bags

by Nicola Temple on September 29, 2011

Plastic bags are the urban environmentalist’s nemesis. Constructed from fossil fuels, these convenient carriers often end up in the environment, contributing to litter in our streets and travelling down our waterways to become dangerous debris in our oceans. The introduction of biodegradable plastic bags seemed hopeful in the battle against this plastic plague; however, all was not as it seemed.

Some biodegradable bags aren’t truly biodegradable. For a plastic bag to be considered biodegradable it must degrade to a point where microorganisms can then metabolise what’s left.

Biodegradable plastics include bioplastics, which are made from renewable crops such as corn, and can be starch-based or cellulose-based.

However, there are also petroleum-based plastics that are labelled biodegradable. They have additives that help them degrade into smaller pieces of plastic, but it doesn’t necessarily mean they are biodegradable.

How to tell your biodegradable plastic bags apart

Bioplastics are completely compostable and are usually sold as compostable plastic bags. They are not dependent on fossil fuels and although they release CO2 into the atmosphere when they degrade, the crops used to produce them sequestered carbon while they were growing. Therefore, they are considered to be relatively carbon neutral. However, like biofuels, concerns have been raised about using important agricultural land for growing crops intended to support consumptive habits of developed countries.

Oxo-biodegradable plastics are petroleum based. Metals, such as cobalt, iron, and manganese, are added to the plastic and when these metals are exposed to sun and oxygen, they will become oxidized and cause the fragmentation of the polyethylene. This degrades the bag into very small pieces in an infinitely shorter time frame than would otherwise occur. As the degradation process is dependent on oxygen, these bags will NOT degrade in an anoxic environment like a landfill. Also, because they are petroleum based, they remain dependent on fossil fuels.

In 2010, Loughborough University, in the United Kingdom, conducted a study that examined the effects of oxo-degradable plastics.  The report spurred concerns about whether the minute pieces of plastic could be consumed by insects and other small animals. The plastic would then enter the food chain and potentially bioaccumulate causing toxicity issues in animals. Another major concern was that these types of plastic are not suitable for conventional recycling due to the additives used to speed up the degradation process; however, they are also not suitable for composting.

biodegradable plastic bags

Biodegradable plastic bags need to be disposed of properly otherwise they end up as unsightly tree ornaments like this...or worse. CC image courtesy of Eric on Flickr.

Proper disposal of plastic bags

Non-degradable plastic bags should be recycled. If grocery stores supply plastic bags, they usually have a collection program as well, so be sure to use it. They will then be transferred to a recycling facility capable of dealing with this type of plastic.

Bioplastics need specific moisture, oxygen and light conditions to compost properly. They are usually not suitable for home composts as they take longer to biodegrade, however, they can usually be disposed of in municipal composting facilities.

Most importantly, biodegradable and compostable plastics have to be separated out from non-degradable plastics as they can interfere with recycling facilities. Keep this in mind if you are dropping plastic bags off to the grocery store for recycling and don’t include any bags labelled as compostable or biodegradable.

There has been such confusion about the labelling of biodegradable plastic bags that in 2008 California prohibited the sale of bags labelled as biodegradable, degradable or decomposable. They released a compostable plastics fact sheet that stated that plastics can be labelled as compostable or marine degradable “but must meet the requirements of the appropriate American Society for Testing and Materials.”

Biodegradable plastic bags that are compostable are an opportunity to reduce our dependency on fossil fuels and reduce the amount of persistent plastics in our environment. However, their production and their disposal still carry some environmental challenges. Reducing or eliminating the use of plastic bags is not an insurmountable task. There are lots of alternative carrier bags that make the plastic carrier bag obsolete. Perhaps this mockumentary will detail the life of an endangered species…let’s hope so!


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