Plastic confusion: All you need to know about biodegradable and compostable plastics

Thursday, 12 July 2018

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When Simon Upton came back down to New Zealand last after a long stint overseas, he was gobsmacked by the amount of plastic we use.

The country's new Parliamentary Commissioner for the Environment went to a supermarket and the first bag he picked up was labelled biodegradable.

'I thought 'What does that mean?'' Upton said.

So the man with powers to investigate environmental concerns thought if he didn't know, other people probably didn't either.

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Upton was also 'gobsmacked' by the amount of plastic used in New Zealand - he'd been working for the OECD in Paris as Environment Director since 2010.

Given the confusion around biodegradable and compostable plastics and growing concerns about the scale and lifetime of plastics, Upton has gone out to clear the air.

In a letter to Associate Minister for the Environment Eugenie Sage and Minister for the Environment David Parker, Upton said the combination of widespread single-use plastic in the retail sector and growing public concern were 'a fertile climate for the promotion of plastics that are said to be biodegradable, degradable or compostable'.

He said the terms 'can become a serious source of confusion and even lead to worse environmental outcomes'.

'The results of my enquiry suggest that both businesses and consumers face a bewildering array of claims about plastic that can lead to misunderstandings on the part of even the most environmentally conscious citizens.'

Upton also highlighted four areas regarding biodegradable plastics that needed 'urgent attention': Sorting out the terminology, standards and labelling, end of life infrastructure - including recycling, composting, and landfill facilities, and clarity of environmental goals.

In order to avoid confusion on the issue, in his latest report he's laid out the details of biodegradability and compostability and how they work.

It's a lengthy document in Q&A format, so we'll summarise them.

While the original document is long, it is a one-stop shop for what you need to know.

What does it mean to say that a plastic is biodegradable?

Biodegradable means that an item can be broken down by the action of living organisms, typically microbes. In the case of biodegradable plastics, this process is enabled by enzymes that are produced by microbes that use the plastic as a source of energy – the microbes are essentially eating the plastic for food.

Plastic piled up at the Huntly Transfer Station in early May.

New Zealand does not have a standard for biodegradable or compostable plastics. However, some plastic manufacturers have voluntarily sought certification using some of the existing international standards so that they can label their products accordingly. An industry working group has been set up to consider whether adoption of a standard in New Zealand would be useful.

What do biodegradable plastics break down into?

Ultimately, a biodegradable plastic will break down into small molecules, such as carbon dioxide, methane and water, as well as waste from microbial activity.

Plastics, including biodegradable ones, often have other components mixed in as 'additives' for various reasons. These additives may be released when the plastics degrade.

What does it mean to say that a plastic is compostable?

Parliamentary Commissioner for the Environment Simon Upton.

Composting involves the breakdown of biological material such as green waste from garden clippings or food scraps into humus.6 Industrial compost facilities are designed to accelerate microbial growth by controlling moisture, airflow, microbial activity and the proportions of different organic wastes. As the microbes consume the waste, they generate heat, which accelerates the breakdown. The resulting product, compost, is then used to return organic matter to the soil.

Home composting involves a similar process but on a much smaller scale, so it may not generate as much heat and will likely result in a slower breakdown process

What does it mean to say that a plastic is certified as biodegradable?

A product that is certified biodegradable should meet a robust international standard. Examples of such standards include those that apply in Europe and Australia.

These standards include a range of tests for biodegradability that consider different receiving environments, such as wastewater treatment plants, freshwater or marine environments.

What does it mean to say a plastic is certified as compostable?

Products that are certified compostable will usually have been tested in commercial composting conditions. They will not necessarily biodegrade in a home compost heap.

Standards for home composting are very different in respect of the length of time over which products are tested for and the temperatures required. Few home composting standards exist.

A product that is certified as compostable should meet a robust international standard.

Do plastics have to be bio-based to be biodegradable or compostable?

No. These plastics can be made from biological sources, such as plants or microbes, or fossil sources. Biodegradability and compostability is a matter of chemistry, the disposal environment and time.

What types of plastics are biodegradable or compostable?

Biodegradable bio-based plastics - Polylactic acid (PLA), Poly(hydroxyalkanoates) (PHAs), Thermoplastic starch (TPS). Biodegradable fossil-based plastics - Polybutylene adipate terephthalate (PBAT), Polycaprolactone (PCL).

What types of plastics are not?

Non-biodegradable fossil-based plastics, Oxo-degradable plastics and Non-biodegradable bio-based plastics - PET is partially bio-based but not biodegradable.

What happens when biodegradable or compostable plastics end up as litter?

While some certified biodegradable or compostable products can be completely broken down into benign molecules within a reasonable timeframe, this will only occur under the right conditions. The presence of heat, moisture, and microbes would help create favourable conditions.

For example, while a biodegradable coffee cup may break down within several weeks in a carefully controlled commercial compost facility, the same cup may take decades to break down in the ocean.

Which plastics can I compost?

Some plastic products have been tested and are certified to break down in home compost bins. However, there are currently no guidelines or recommended methods for home composting. Most certified compostable products are designed to be processed in industrial composting facilities at the end of their usable life, where the temperature, moisture and oxygen levels can be carefully controlled.

Can I recycle biodegradable plastics?

Some types of biodegradable plastics can be recycled, others cannot. Biodegradable plastics can cause problems for recyclers if they get mixed up with plastics destined for recycling because they can render these unrecyclable. It all depends on the type and amount of biodegradable plastic.

Some challenges for recycling include PLA, oxo-degradable plastics and starch-based plastics.

What happens if biodegradable or compostable plastics end up in a landfill?

In New Zealand, municipal general waste landfills receive the bulk of domestic waste, including many types of plastics.

Because composting and recycling biodegradable products can be challenging and demanding, much of this packaging currently ends up in landfills. The extent to which a biodegradable compostable plastic will break down in a landfill depends on the amount of air, water and microbial activity. Digestion occurs at highly variable rates and sometimes not at all.

So am I making a difference by putting biodegradable or compostable products in the right bin?

The bin you choose matters. However, how much you help the environment depends on how good the disposal services that will deal with your rubbish are.

Are biodegradable or compostable plastics better for the environment than conventional plastics?

It depends. Biodegradation means that the plastic will not persist in the environment for as long.

However, it should not be viewed as a way of dealing with litter. If littered, even certified biodegradable plastics may not break down in the way expected.

Composting may be a way of diverting waste from landfill, but the ability to deal with compostable plastics depends on the availability of facilities to process this waste. Compostable or biodegradable plastics may contain additives.

If additives are present, ultimate biodegradation into small molecules may not be possible within timeframes that reduce or remove their environmental impact.

There are also questions around the climate change implications of breakdown of biodegradable and compostable plastics.

Are bio-based plastics better for the environment than fossil-based plastics?

There is no simple answer to the question of whether bio-based plastics are better than fossil-based plastics, as the entire 'life-cycle' of any alternative must be considered and contrasted.

Are there any solutions to the problem presented by single-use plastics?

Use less of it!

What can I do if I think a business is making a false, misleading, or unsubstantiated claim about a product?

You can ask the business to provide evidence for its claim – it must be able to back up its claims.

If you are still concerned that a claim being made is potentially misleading or false, you can complain to the Commerce Commission.

What are the climate change implications of biodegradable and compostable plastics?

There is a fundamental difference between fossil-based and bio-based plastics in terms of the production of greenhouse gases. Even when a fossil-based plastic completely biodegrades, it will be adding new carbon dioxide to the atmosphere.

By contrast, a bio-based plastic that completely biodegrades will effectively simply cycle the carbon that was removed from the atmosphere when the plant grew – i.e. this is a carbon-neutral process that does not add any more carbon dioxide to the atmosphere.

Both types of biodegradable plastics could produce methane, a potent greenhouse gas, if they decompose under anaerobic conditions.