When you hear the word “biodegradable”, what’s the first thing you think about?
The tea bags and egg shells in your compost heap at the end of the garden? The soggy and rotting leaves from an autumn forest?
How about the plastic cutlery you eat your lunch with, or the lid on your coffee cup?
Biodegradable polymers are seen by many as the solution for the world’s throwaway society. These plastics are touted to break down in the environment, just the way leaves rot away after falling from the tree outside your house. In a culture obsessed with single-use plastic, these materials seem to be the solution- no guilt needed in forgetting your reusable coffee cup if the disposable one will just rot away, right?
When the term “plastic” in its modern context was first coined by Leo Baekeland in 1909, he never could have imagined the revolution that would take place. His industrial plastic Bakelite would take the world by storm, as the plastic that begun the Plastic Revolution.
Before Bakelite, no other material had been so fire-resistant and hard at such a low price. Nitrocellulose, an early polymer that built Hollywood’s tape reels, was so flammable it caused the deaths of 123 people in the November 1929 Cleveland Clinic Fire. An inert, cheap, customisable material like Bakelite was useful as electrical insulation, the body of a telephone or colourful jewellery.
From there, polyethylene (PE), polyethylene terephthalate (PET) and expanded polystyrene foam (PS) were discovered and commercialised, enabling a one-use culture. In 1955 Life Magazine published a now ominous editorial claiming that the items pictured thrown in the air “would take 40 hours to clean- except that no housewife would bother” since every single item was disposable. This lust for convenience has become ingrained in our culture to this day.
Modern day plastic bags and convenience culture
Before the introduction of Britain’s 5p plastic bag charge in October 2015, the public used eight and a half billion single-use plastic bags to take their shopping home in 2014. This weight of 68,600 tonnes is over 1kg of thin plastic bags per person in the entirety of the UK’s estimated 64.6 million people in a single year.
These plastic bags are usually made of polyethylene; made from a byproduct from crude oil, these small molecules join onto themselves end to end to create super-long carbon chains when at hundreds of atmospheric pressures.
When these chains reach thousands of chain links long and certain additives are melted into the polymer, the melt becomes plastic (or mouldable) and unreactive- perfect for a plastic bag that needs to stay in one piece while carrying all sorts of food or drink.
The PET that makes up your bottle of fizzy drink needs to be inert, or it will react with the water it contains and break down. It also must be strong enough to hold the pressure of the fizz without exploding.
The use of these plastics has enabled perishable food to last, cables to be covered in cheap insulation and hospitals to be super hygienic with one-use syringes and pill packaging. Plastics have enabled society to become more efficient and much faster, but these benefits always come with a cost.
Plastic’s effects on the planet
It wasn’t until recently that the issue of plastic pollution was fully realised in the public eye. When the BBC’s Blue Planet II aired an episode on the human race’s impact on the oceans, the world saw the real impact of single-use plastic. Heart-wrenching shots of turtles trapped in fishing nets and the stomachs of Wandering Albatrosses being filled with inedible plastic galvanised the nation to ditch one-use plastic straws.
Sir David Attenborough was very vocal about the observations of the Blue Planet II team around its launch, hoping everyone watching would see “that we have a responsibility” to tackle the plastic pollution in our oceans.
Mere months after the broadcast, in May 2018, the European Commission proposed a bill to eliminate single-use plastic from the entire EU. By this point, the five pence plastic bag charge had been law for around two and half years in the UK, reducing their usage by 83%10.
“It is one world. And it’s in our care. For the first time in the history of humanity, for the first time in 500 million years, one species has the future in the palm of its hands. I just hope he realises that that is the case.8”Sir David Attenborough to The Independent in October 2017
Growing economies in the east and their plastic consumption has far outpaced the west’s loss of appetite. The top 6 plastic waste polluters surround the South China Sea and between them release 2.75-7.35 million metric tons of plastic waste per year into the ocean, as of 2010. This was predicted to increase tenfold by 202511.
But what if this plastic degraded into simple compounds, like those tea bags in your compost heap?
“Biodegradable” as a label is so complex, the lack of definition is a very real issue through the plastics industry.
Terms like “fair-trade” see such intense regulation that rigorous background checks must be completed before the label can be applied to a product; the same cannot be said for “biodegradable”. No real regulatory bodies exist for this term, and as such several definitions are out there with a wide range of possible testing conditions.
Materials that degrade in the absence of oxygen, in environments like landfill or the deep sea, are very distinct from ones that degrade in the presence of oxygen in the way leaves do in the autumn.
Some regulations simply check the sample visually after some time; others measure the carbon dioxide released as the plastic breaks down. Temperatures of tests can range from 15-28°C in some saltwater tests and 55±5°C in freshwater ones.
The lack of independent verification allows manufacturers engineer the conditions of their degradation experiment, letting them grind plastic into a powder for a bigger surface area or select specific strains of bacteria in unnaturally high concentrations to give the best results.
This is a huge problem. Plastics can be called “biodegradable” due to a test that may be near-impossible to replicate in nature. The plastic bag you take your shopping home in may biodegrade with industrial composting, with constant aeration and temperature, but likely wouldn’t degrade in the ocean– where a large amount of mismanaged plastic waste ends up.
Many companies since the 1980s have been accused of “green-washing” or using environmentally-friendly buzzwords to appeal to a more conscious consumer. This influence is dangerous, and can result in wrong assumptions about a material- especially when based on bad science.
The British government has recognised this issue and has called for new official standards to be imposed.
Oxo-biodegradable plastics have been advertised as a quick-fix for the plastics crisis. These are made of materials that break down when subjected to heat or UV light, usually with additives that enhance this oxidative degradation. When these plastics fragment into smaller pieces they are much more biodegradable, and seemingly disappear to the naked eye.
These oxo-biodegradable materials are of great concern to many in the business of biodegradable polymers as there are- again- no official regulations safeguarding the term ‘oxo-biodegradable’. The additives used to promote oxidation are often toxic heavy metals, like cobalt or manganese, which become released into the environment as the material breaks down rapidly.
When the European Commission published its review of oxo-biodegradable plastics in January 2018, the conclusion was damning: oxo-biodegradable plastics should be banned in the EU.
Not only this, but the material will eventually break down into invisible fragments, or microplastics, identical to those in conventional plastics documented climbing the marine food chain when shrimp mistake the particles for plankton. We could end up eating the plastic bag we thought would disappear completely when we threw it away.
It’s not all doom-and-gloom though; plastics made from plants may serve useful in single-use packaging. Read about them here in a few weeks.