What are the problems with biodegradable plastic?


The dictionary definition of ‘biodegradable’ is “capable of being decomposed by bacteria or other living organisms”.

Plastic, being a man-made material, is not biodegradable. Bacteria that will happily munch through food, paper or wood, will ignore plastic because it does not recognise it as food.

Rather than biodegrade, plastic decays when exposed to sunlight, in a process called photodegradation. And it takes a long, long time.

When exposed to sunlight, plastic bags break into smaller and smaller pieces, until they are classed as microplastics.

Prolonged exposure to sunlight will cause the plastic to break into smaller and smaller pieces until you’d need a microscope to be able to see them. Plastic particles that are measured at 5 mm or under are known as microplastics.

Scientists are unsure as to whether plastic ever truly disappears. Estimates put the lifespan of plastic at around 1000 years, but nobody knows for sure. The molecular bonds of plastics are so strong that they may never truly completely separate.

Given the durability of plastic, it is perhaps unsurprising that the world is being suffocated by it. Each year, the world’s plastic production increases. Plastic has been found on a polar ice cap, at the summit of Mount Everest, and at the deepest part of the ocean. It has permeated every corner of Planet Earth.

What, then, is the solution to this environmental catastrophe?

In recent years, much has been made of the advent of ‘biodegradable plastic’ as a potential solution to the plastic pollution problem.

But is it all it’s cracked up to be? Could biodegradable plastic be the saviour we’ve all been waiting for? In this article, we take a look at the facts about biodegradable plastic.

The big problem with biodegradable plastics

Jacqueline McGlade, chief scientist at the UN Environment Programme called biodegradable plastics “well-intentioned but wrong”.

Biodegradable plastic will not decay in the ocean; there’s not enough heat or sunlight

Seeing the word ‘biodegradable’ on a piece of plastic might lead people to believe that it will just naturally decay over time, the same way as a banana might. Unfortunately, this is not the case. For this type of plastic to biodegrade takes exposure to high temperatures and sunlight.

Biodegradable plastic is designed to decay at temperatures above 50°C, which means it is not going to biodegrade if it enters the ocean. In fact, it’s not going to biodegrade anywhere other than in specialist facilities.

Another issue is the fact that the process requires sunlight to work properly. Biodegradable plastics are not buoyant, meaning the plastic will sink in the ocean and not be exposed to sunlight. It also means they won’t decay when buried in a landfill.

Perhaps a better label for these products would be ‘biodegradable, but only under certain strict conditions’.

Built to self-destruct

Concerns have been raised about the very concept of biodegradable plastics.

The European Plastics Recyclers Associated said recently: “Plastic bags take a lot of energy and oil to make so why waste them by creating bags that self-destruct?”

Biodegradable plastic encourages people to think of plastic as a disposable material and risks us going back to the ‘single-use’ mentality.

A better approach is to think of plastic as an incredibly valuable material, only to be used when absolutely necessary. Otherwise, we should all be following the mantra “recycle, reuse, reduce”.

The environmental cost of bioplastics

There is controversy surrounding the environmental cost involved in the production of bioplastics.

Large quantities of corn are needed to produce polylactic acid

To make 1 kg (2.2 lb) of polylactic acid (a commonly used bioplastic) requires 2.65 kg (5.8 lb) of corn.

Currently, around 270 million tonnes of plastic is produced every year. If this quantity of plastic came from corn-based sources, it would require around 715 million tonnes of corn. That’s a huge amount of the world’s food supply, particularly at a time when global warming is making farming more difficult in tropical areas.

Compostable, but…

Biodegradable plastics are often listed as ‘compostable’, giving the impression that you should be able to just toss them onto the compost pile like you would a banana peel, and it will disappear in a matter of weeks. Sounds great, right? Unfortunately, it’s a bit more complicated than that.

Biodegradable plastic requires an industrial composting facility to efficiently decay

As discussed previously, biodegradable plastics need very specific conditions to be able to decay as intended. For this reason, biodegradable plastic is intended to be processed at industrial composting facilities – not your backyard.

If you’re curious whether you have an industrial composting facility in your area, take a look at http://www.findacomposter.com/

If there are no industrial composting facilities in your area, then biodegradable plastics will be heading to landfill, where they won’t be subject to the conditions necessary for decay.

What is the difference between biodegradable plastics and bioplastics?

It is important to draw a distinction between ‘biodegradable plastics’ and ‘bioplastics’.


Bioplastics: the future of the plastics industry, or part of the problem?

Common plastics are made from petroleum or natural gas, whereas bioplastics are made from renewable biomass sources such as sugarcane, wheat, or corn.

The ‘bio’ in bioplastics refers to biology, as in they are derived from biological organisms.

In fact, the very first plastics were made from plants, using their own internal chemical synthesis. Rubber, for example, is derived from the rubber tree and is technically a plastic. The very first plastics were developed in an attempt to replicate existing, natural materials, such as rubber and tortoise shells.

Bioplastics largely took a back seat to petroleum-based plastics, due to the latter being less expensive and more efficient. However, due to growing concerns about global warming and the finite nature of fossil-fuels, bioplastics have made a comeback in recent years.

Biodegradable Plastics

Unlike bioplastics, which are made from biomass sources such as sugarcane, biodegradable plastics are made from the same source as conventional plastics: petrochemicals.

During the production of biodegradable plastics, chemicals are added that cause the plastic to break down quickly when exposed to air and sunlight.


The definition of greenwashing (according to Wikipedia) is “is a form of spin in which green PR or green marketing is deceptively used to promote the perception that an organization’s products, aims or policies are environmentally friendly.

That’s exactly what is happening in the case of biodegradable plastics. Yes, technically they are biodegradable, but the conditions under which the plastics will biodegrade are so specific that it is unrealistic to think of this as a viable solution to the plastic pollution problem.

What happens when biodegradable plastic enters the ocean?

Biodegradable plastics in the sea will behave very similarly to regular plastics because the conditions required for biodegradation are very unlikely to occur.

This seal was found with a plastic ring lodged firmly around its neck

Many different species of marine animal are adversely affected by plastic in the sea, including whales, sea turtles, seabirds, and fish. Plastic has been found inside the guts of many animals, and it is thought to result in the death of 100,000 marine animals every year.

As well as the dangers associated with ingesting plastic, marine life also faces the threat of becoming entangled in plastic, hindering their ability to swim, hunt, or fly. They either become easy targets for predators, or they lose the ability to feed themselves and die slowly from starvation.

The future

The science of biodegradable plastics is advancing at a rapid rate.

If scientists can figure out a way for plastics to decay under normal conditions, including in the ocean, it could be a breakthrough in the fight against plastic pollution. It would still be prudent to ‘recycle, reuse, reduce’, but to have plastic that we knew would not last for centuries could help avert the environmental catastrophe we find ourselves in.