Degradable, Biodegradable & Compostable Bags

DEGRADABLE, BIODEGRADABLE & COMPOSTABLE BAGS

Plastic bags are under the spotlight at the moment... they are endangering our oceans and the wildlife that live in them, littering our planet, they take hundreds of years to break down, and when they do, it is often into small pieces of micro-plastics. These micro-plastics are contaminating our environment, finding their way into the fish and animals that we eat, even into our drinking water, and therefore into our own stomachs and bodies. The ongoing effects of this plastic exposure, and the chemicals they introduce into our bodies, is yet to be determined, but it is unlikely to be good news...

There are lots of bags out there claiming to be "environmental" but what exactly to the claims of "degradable", "biodegradable" and "compostable" actually mean.

Degradable or 'oxo-degradable' plastic bags

Degradable bags are made from plastic with other chemicals added (this can even include heavy metals). These additives allow the plastic to break down and disintegrate over time when exposed to sunlight and heat, generally quicker than a standard plastic bag would. These bags break down into hundreds of tiny pieces of plastic (microplastics) which are released into the environment. Animals and marine life can consume the smaller pieces of plastic more readily than they would if the bags were still whole, they therefore enter the food chain, turning up in seafood and animals eaten by humans... microplastics are now everywhere, including our drinking water.

It is also much more difficult to remove the hundreds of tiny pieces of plastic from the environment.

A quick web search will reveal degradable bags still being sold under labels such as "green" or "environmental" and even "planet safe" or that the "protect the environment" when they may be worse for the environment.

Degradable bags should only be placed into your landfill / general waste bin. They cannot be recycled.

Biodegradable Bags

These are bags that are capable of being decomposed by bacteria, fungi or other living organisms, leading to the production of carbon dioxide, water, methane, biomass, and mineral salts. These plastic bags can be made by extracting sugar from plants like corn, cassava or sugarcane to convert into polylactic acids (PLAs) , or polyhydroxyalkanoates (PHAs) engineered from microorganisms.

But just because something is biodegradable does not mean it’ll break down immediately, or even quickly. The process takes time and depends on the conditions in which the biodegradable plastic ends up.
The conditions required for biodegradable bags to break down include higher temperatures of 50 degrees Celsius and exposure to UV light - conditions not found in marine environments nor landfill, and rarely met in the natural environment. They will therefore generally require high temperature industrial composting facilities to break them down. In the absence of oxygen (think landfill - an anaerobic environment) the bioplastics, deprived of oxygen, can release methane, a greenhouse gas 23 times more potent than carbon dioxide.

Biodegradable bags are not compostable – it will contaminate your green organics bin.
Biodegradable bags should be placed into your landfill / general waste bin.

COMPOSTABLE BAGS

A compostable material, can be broken down microbial digestion to create compost. Compostable bags are made of natural plant starch, and do not produce any toxic material. They break down readily in a composting system through microbial activity to form compost.

To claim a product is fully compostable it must meet the specifications which require that the products completely decompose in an industrial composting setting in a specific time frame, and leave behind no harmful residues.

The European Norm EN 13432
The US Standard ASTM D640
The Australian Standard for compostability AS 4736

Industrial composting generally takes place in industrial or municipal composting plants. Conditions are controlled, i.e. controlled temperatures, humidity, aeration, etc. for a quick and safe composting process.

Home compostable Bags
In Australia Bags marked with the AS 5810 symbol are compostable through your green waste bin, and can go in your home compost system (Home compostable).
In the European Union, bags marked with the EN1342 seedling logo can be put in your food and garden bin. These bags are made from potato starch so break down at the same rate as food and garden waste.

Landfill
Compostable materials don’t break down as easily in a landfill environment - there can be lower temperatures than required, less oxygen, and perhaps fewer microorganisms - so the breakdown of plant-based waste (which includes compostable bags) in landfill can take a lot longer and can lead to increased methane emissions. Thankfully, though, they do not break down into micro-plastics.

Recycling
Remember that if compostable packaging/bags get into the recycling stream, it can contaminate all the other materials, meaning that the whole batch cannot be recycled.

Buying Home COmpostable bags

Happily, there is a growing number of choices and range available for home compostable bags.
Always check that bags are "home compostable" (not just "industrial compostable" or "compostable") if they are going into green waste.