Time to ban biodegradable plastic?

Colin Williamson explains his plea to stop using biodegradable plastic: ‘Please don’t use them, don’t recycle them and don’t tell me how wonderful they are.’

In the 21st Century drive for sustainability, the concept of biodegradable plastics seems fantastic. The iconic man-made product reverting to nature seems too good to be true. And, of course, like anything that seems too good to be true, it probably is.

Biodegradable plastics do exist, of course, made from agricultural materials or made by modifying conventional petrochemical based materials. Now, for the sake of simplicity I have ignored the degradable plastics based on oil, as they use more energy than normal products as well as exhibiting the other problems mentioned below. But, rest assured, any claims of biodegradable plastic eco-efficiency are based more on politics and economics than mathematics. So let's look at the big picture.


Most scientists accept global warming is the biggest environmental threat to human life. We measure this by the carbon footprint over the lifecycle of a product or system. So, let's consider the carbon footprint of some plastics products by comparing the lifecycle of a biodegradable plastic bag or bottle with one made from 'traditional' oil based plastics.


Oil is pumped from the ground, refined into plastic and made into a product. It uses energy to make the transformation of course and this can be added to the energy embedded in the oil itself. Alternatively, corn is grown by a farmer who uses energy to drive his tractors and chemicals to spray the plants. After

harvesting the corn is converted to a plastic product by an industrial process, which itself uses more energy.

We can calculate the total amount of energy expended in making a bottle or bag. If the packaging is oil based it probably weighs less than the biodegradable alternative so an allowance has to be made for this.

Few independent eco-audits have been conducted on biodegradable plastic products though, and we still have yet to discover

the true eco-footprint made by agro-sourced plastics. Some bio-sourced plastics are based on a waste product from the agricultural industries, such as bagasse, and claim a zero carbon footprint, others are made from foodstuffs.

When the packaging has fulfilled its primary function it becomes waste, and that's where it gets interesting. Most waste in the UK ends up in landfill site, so let's consider what happens once the stuff gets buried. Oil based plastics may take centuries to degrade but until then they stay inert, just like a lump of rock or stainless steel. In other words they have no further effect on the environment.

The biodegradable bag or bottle on the other hand starts to degrade relatively quickly (although nowhere near as quickly as the manufacturers claim – just try it if you don't believe me). It biodegrades, not just to carbon dioxide (CO2) and water as there is little oxygen in a landfill site, but to other chemicals that escape as complex molecules and gases, normally methane.


Methane is one of the powerful 'global warming' gases, about 24 times more damaging than CO2. Recent EU directives relating to landfill sites acknowledge this by limiting and restricting the amount of biodegradables (especially garden refuse) going to landfill. There are other significant issues with biodegradables in landfills including land instability and leachates into the water table.

So which is better, a bottle in a landfill site that has no further influence on the environment or one that biodegrades to a harmful global warming gas?

What about recycling?
And as we recycle more and more waste, including plastics bottles and bags, one of the well-established uses of old polyethylene bags and film is to be recycled in to black builders' film to be used as damp-proofing. Imagine what would happen if biodegradable bags get mixed into this recycling stream.

The recycler can't differentiate between the biodegradable bag and the standard one so he makes and sells the sheets that then gets used under a floor in a new building. This is the ideal situation for degradation to start and the film develops a hole and no longer is a water barrier, the house gets a damp patch and no-one knows why. So the presence of biodegradable plastic carrier bags in the recycling waste stream is seriously impacting the recycling industry.

In some countries where biodegradable bottles have already been introduced, major problems are being encountered by the recyclers who have already taken billions of bottles out of the waste stream for recycling.

"Hang-on", I hear you say, "these biodegradable bottles can be put in the green waste collection bins to be composted?!" Well, yes, they can, but the guys doing the composting remove any plastic and discard it for landfill as they cannot differentiate biodegradable from traditional plastic.

Biodegradable plastics sound wonderful, but are largely a brilliant marketing concept. If landfilled they contribute greatly to global warming, if recycled they are a major hindrance to existing recycling schemes we have battled so hard to encourage.

Biodegradable plastics will have their uses, of course, but only when their end uses are clearly identified. One is as the bags for local authorities to collect garden refuse for composting. Ordinary polythene bags are normally used, but as they don't biodegrade, they have to be emptied of their contents, either by the collectors or at the composting facility. Biodegradable bags would be excellent for this application, able to be properly composted and unlikely to enter the recycling stream.

If you can think of any other suitable uses, please let me know, but until then: please don't use them, don't recycle them and don't tell me how wonderful they are.

About the author: Colin Williamson is technical consultant at Smile Plastics, a dedicated plastics recycler.

Author
Justin Cunningham

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Do you have any comments about this article?
As much as the author claim s the danger of biodegradable plastics, the problem we are currently facing in regard with the protection of the enviroment, wildlife and marine life is not oroperly adressed just plasti ad plastic before we even go to the after-effects, plastic recyclers should stress more emphasis on educating people and get involved in school programs all the more.

Comment Thulani, 14/09/2017
Are you guys saying plastic is good? and compostable products that can be broken down bacteria or microbes bad? Nature is perfect, god made it that way and man's interference screws it up. If we want to fix this we have to mimic nature.

Comment Batman, 19/03/2016
How can you say that a regular plastic bottle has "no further influence on the environment"? The effects of plastic pollution and how it's poisoning the earth are well documented.

Comment Ari Einbinder, 13/03/2015
There are 3 types of biodegradable plastics- plant based, oxo or oxy degradables, and landfill-degradables. The first 2 cannot be recycled with main stream plastics, where the third can be. In the US, we use natural gas to make a lot of our plastics, not oil.Plant based plastics need commercial and municipal composting if they are ASTM 6400 so I personally do not like them as the corn based ones are driving up the cost of food.Landfill biodegradable plastics do produce methane which can be captured and converted into electricity. There is a BMW plant in SC that has a pipe line from a landfill to the plant delivering methane which they use to run 60% of the plant. This is also being done in Europe (Sweden, and Germany). So please don't include landfill biodegradable plastics in the "do not use" column. They are a source of renewable energy that is cheaper than solar, wind, and most other energies, can be safely recycled, and can break down anaerobically to produce methane that can be captured. In the US, we are converting more and more landfills to do this as well as composting centers.

Comment Leslie Harty, 06/03/2015
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