You're trying to do the right thing by the earth, but when you get to the shelf in the supermarket to buy bin liners, it can get confusing.
Plant-based sounds like it should be good, but then there's also degradable, biodegradable and compostible. What's the difference?
Warwick Hall from the Australasian Bioplastics Association (ABA) provided these answers to help you choose the right bin liner for you.
- Please explain the difference between plant-based, degradable, biodegradable and compostable.
Bioplastics can be renewable resource based, organically recyclable including compostable, or both. So there are products which are made from renewable (plant) based resources that are organically recyclable and there are those made using fossil fuel resources that are also organically recyclable. However there are products made from renewable resources that are not designed to be organically recyclable. Most organically recyclable bioplastics are made using a combination of renewable and fossil resources with the renewable content increasing as time goes by.
Degradable does not mean anything. It is difficult to think of anything that is not degradable. Even steel oxidises and degrades. Most often with plastic films or bags, it is used to describe conventional plastics, usually polyethylene, which include additives to cause fragmentation under some circumstances. The resulting fragments are not biodegradable, will persist in the environment for many years and add to the well-known marine and terrestrial plastics pollution problems.
Biodegradable also means little without qualification of conditions, time, extent of biodegradation and products of biodegradation. It could be that an item will biodegrade to an extent, leaving a residue that is toxic to some life forms. It may biodegrade only to a small extent over a very long time. For that reason, standards have been developed that prescribe conditions, extent, products of biodegradation and toxicity for materials or products to be tested against and have their performance verified.
- Can you put compostable bin liners in your home compost?
Home composting conditions vary much more than do industrial composting conditions. Even though bags and liners which carry the AS4736 industrial compostability logo are by definition biodegradable and will biodegrade in home composting conditions, the preferred product is a liner that carries the AS5810 home compostability logo, which demonstrate that the product has been tested and verified to meet the requirements of the standard.
Bear in mind that because home composing conditions vary so much from someone throwing everything into a corner to well-run home composting conditions and everything in between, the rate at which the home compostable liner will biodegrade will vary, just as it does for the tomato or other organic matter.
- What standards apply to manufacturers using these terms?
In Australia, the relevant ones are AS4736-2006, Biodegradable Plastics - Biodegradable plastics suitable for composting and other microbial treatment addressing industrial organics recycling including composting, and AS5810 - 2010 Biodegradable Plastics - Biodegradable Plastics suitable for home composting addressing home organics recycling or compostability.
The ABA runs verification programmes to the requirements of both AS4736 and AS5810 and provide licensing opportunities for logos to be applied to products. The Australian Organics Recycling Association (AORA) endorses plastics so labelled as acceptable inputs into their organics recycling processes. Many local governments demand certification to AS4736 or AS5810 for suppliers of organics waste collection liners and bags, for example the liners in ventilated food waste collection kitchen caddies and larger bags.
- What do you think is the most sustainable option?
It is easier to explain what is not sustainable and that is degradable or oxo-biodegradable bags. As noted above, these are not biodegradable and add to the environmental plastics pollution problems. Further, they are not an acceptable input into conventional plastics recycling and have been listed for banning in the EU.
On the other hand, organically recyclable or compostable bioplastics are more often that made using an increasingly high level of renewable resources, biodegrade in industrial and home composting, breaking down to carbon dioxide, water and residual biomass, just the same as a tomato or lettuce. The resultant compost can be applied to the soil in large scale to agricultural land or smaller scale to the home garden, recirculating the carbon and adding to the quality of the soil.