Oxo-biodegradable plastics might not cause harm as obvious as this, but they are by no means harmless.
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Frontline Online: Plastic not-so-fantastic
February 18th, 2013
by Lorna Howarth
Why Pakistan’s recent announcement of a ban of non-biodegradable plastics may not be beneficial for the environment. Lorna Howarth reports.....
After the recently published Frontline piece on Pakistan’s ban on non-biodegradable plastics, we’ve had a veritable avalanche of feedback and comment in the Ecologist offices. Obviously, a follow-up piece giving a more in-depth perspective was necessary. Thank you to all the independent scientists and experts who have given their advice and guidance on this piece.
Manufacturers of oxo-biodegradable plastics – the kind that Pakistan is now introducing for all disposable plastic products – claim the material initially breaks down into small pieces which eventually disappear when exposed to sunlight and oxygen over several months. But, when we look closer into how oxo-biodegradable plastics break down, it seems another story emerges.
Biodegradibility is the ability of a material to be utilized as a carbon source by living microorganisms and converted safely into carbon dioxide, biomass and water. The term ‘oxo-biodegradable’ suggests that the product may undergo biodegradation. However, the main effect of oxidation will be fragmentation of the material into small particles, which remain in the environment. Therefore the term ‘oxo-fragmentation’ may better describe the typical degradation process of this plastic.
Additives added to the plastic granules before extrusion are chemical catalysts containing transition metal salts such as cobalt, manganese and iron, which cause fragmentation as a result of a chemical oxidation of the plastics’ polymer chains, triggered by UV radiation or heat exposure. However, due to high costs of these metal salts and the need to keep the end products competitively priced, reduced quantities are being added to the plastic granules in the production process.
These reduced amounts mean there is a high probability that the complete dispersion of oxidizing ingredients throughout the polymer molecular chain is unlikely. The possible result being that partially micro-fragmented material may occur, and these will not be good for the environment.
The planned use of oxo-degradable additives in plastic films in a semi-tropical (hot and humid) country like Pakistan brings with it many associated shelf stability and storage risks, including the possibility of 'premature degradation’ (disintegrating or weakening the product before it is actually used). Ensuring that the correct amount of additive is used is a serious issue, and can add 3-5 % to the product price, meaning that some less ethical manufacturers may cut corners. The use of oxo-additives in thicker plastics is basically ineffective.
So, it is argued that fragmentation of oxo-biodegradable plastics may not result in a biodegradation process but rather a chemical reaction where the resulting fragments will remain in the environment. This fragmentation is not a solution to the waste problem, but rather the conversion of visible contaminants (the plastic waste) into invisible contaminants (the fragments).
What is more, oxo-fragmentable products can hamper the collection and subsequent recycling of post consumer plastics. In practice, oxo-fragmentable plastics are traditional plastics: the only difference is that they incorporate additives that will ultimately affect their chemical stability. Unless these plastics are identified and classified according to their chemical structure, both conventional and oxo plastics will finish up together in the recycling stream.
In this way, oxo-fragmentable plastics bring their degradation chemical additives to the recyclate feedstock. As a consequence the recyclates may be also become destabilized which hinders acceptance and leads to reduced value of the recyclate.
The European Plastics Recyclers Association (EuPR) and the Association of Postconsumer Plastic Recyclers (APR) therefore warn against oxo-degradable additives. The European Plastics Recyclers Association even went so far as to state that oxo-plastics have the potential to do the environment more harm than good. Some of the major international supermarkets like Tesco and Co-op have stopped using oxo-plastics altogether.
Much of the problem regarding plastic waste is the behavioural tendency to carelessly discard it rather than recycle it. The use of oxo-fragmentable plastics could even stimulate this tendency: after all, ‘out of sight, out of mind.’ The United Nations Environment Programme (UNEP) stresses that littering is a behavioural problem and must be resolved by raising environmental awareness and by the establishment of appropriate waste management systems. Oxo-biodegradable (fragmantable) plastics are not specified as a solution by UNEP.
If oxo-fragmentable plastics are littered and end up in the landscape they start to disintegrate due to the effect of the additives that trigger breakdown, but consequently, plastic fragments are spread throughout the surrounding area. As independent scientific review has not been demonstrated the ultimate biodegradability of this material beyond the micro fragmentation stage, there remains a substantial risk of accumulation of persistent substances in the environment.
Through the impact of wind or precipitation, the plastic fragments can drift into aquatic or marine habitats where they affect organisms and pose the risk of bio-accumulation. In addition, the US National Oceanic and Atmospheric Administration, amongst others, have shown that these degraded plastics can accumulate toxic chemicals such as PCBs, DDEs, as a transport medium in marine environments. Such persistent pollutants in the marine environment have negative effects on marine resources and creep into our food chain.
A recent statement from the Oxo-biodegradable Plastics Association contradicts these findings. It states;
“Oxo-additives, ‘are purported to accelerate the fragmentation of the film products.’ This is a misleading statement, which suggests that the additives do not work at all, or that they simply cause the plastic to break up into smaller pieces of plastic. They [detractors of the technology] know perfectly well that the process of oxidative degradation does work, and that it does not just break up the plastic but changes the molecular structure of the material so that it is no longer a polymer. At the end of that process the material is no longer a visual intrusion, it is no longer capable of blocking drains nor entangling wildlife, and it is not toxic. That is in itself a major environmental benefit, but in addition the material has become biodegradable, and will be bio-assimilated in the open environment by naturally-occurring bacteria and fungi.”
This is obviously a complex and highly contentious issue. The question remains, has Pakistan, with its ban on non oxo-biodegradable plastics, simply substituted one environmental problem with another one? The great irony is that there are more environmentally friendly, cost-effective, biodegradable cellulose plastic options available. Why not legislate for them?
References for this article are available on application.
Lorna Howarth is a writer and environmentalist. She is a contributing editor to Resurgence & Ecologist magazine and the founder of a small independent publishing agency:
The Write Factor www.thewritefactor.co.uk
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