Most people in Australia will be aware of the Plastic Bag Ban which is in various states of effectiveness in South Australia, Northern Territory and the ACT. The Plastic Bag Ban makes exceptions for Compostable Bags which are compliant with Australian Standard AS4736 – 2006. This standard is for “Biodegradable plastics suitable for composting“. This means that Compostable Bags are allowed, where Degradable Bags are not. The question that many people ask is WHY ??? Well, for the answer to this – we need to look at the AS4736 – 2006 standard, to see how they define compostability. In order for a something to be “compostable”, the following 4 criteria must be met: 

  1. Disintegration:  The material must be able to fragment into small pieces below 2mm. This is tested after 12 weeks, and any residue remaining above 2mm must be less than 10% of the original test material’s mass.
  2. Biodegradation: 90% of material must be biodegraded over a period of 180 days. This is measured by the metabolic conversion of carbon to carbon dioxide.
  3. Safety: There must be no evidence of any eco-toxicity or negative effects in the final compost. This can be tested with chemical analysis and plant growth.
  4. Toxicity: The presence of heavy metals must be kept at acceptable levels. This is measured with chemical analysis.

Now the only difference between Compostable Bags and Degradable Bags is with criteria number 2. A Degradable Bag will biodegrade slower than a Compostable Bag in a commercial composting environment. But is the rapid degradation speed in the standard fair? Biodegradation in 180 days is pretty fast. Even some natural items such as leaves can take as long as 1 -2 years to break down! Even a leaf isn’t considered “compostable” by the standard – how appropriate can the standard really be? If the objective of the plastic bag ban is to reduce plastic bag litter, then the exemption of AS4736 – 2006 Compostable bags – at the exclusion of degradable bags is actually counter intuitive and wrong.