Written by: Rose Rattenbury
Growing consumer awareness of plastic pollution combined with high demand for single-use packaging has seen development and availability of biodegradable plastics. Biodegradable plastics can be derived from both petrochemical (non-renewable) sources and renewable sources . The range of biodegradable plastics is large and diverse, represented in Figure 1.
What is biodegradable plastic?
A biodegradable plastic is a material that can break down by natural processes leaving no toxic discharge . Materials are bio-deteriorated, fragmented or assimilated by microorganisms, where enzymes attack bonds in the materials  . When a material biodegrades it produces CO2, H2O, biomass and methane (in the absence of oxygen)   . Microorganisms are specific to the material type . Biodegradation depends on the materials’ size, time and environmental conditions .
The most common and commercialised biodegradable plastics are PLA, PHA, PHB, PHBV, PHV and Thermoplastic starches . These materials are all developed to degrade in industrial compost facilities . PLA, Polylactide is one of the most popular biodegradable plastics and is used as a waterproof lining in paper coffee cups and disposable lids. Despite best efforts to reduce plastic pollution, PLA cannot be recycled, and many commercial composters do not accept it, see Figure 2. If compostable plastic is accepted, then there is usually a business-to-business arrangement whereby the waste supplier includes some decontamination and sorting step before it arrives at the composting facility . Otherwise sorting and decontamination biodegradable plastics is not economically viable for commercial composters .
Biodegradation ≠ Compostable
Many materials biodegrade however, not all biodegradable materials can be composted. For a material to be commercially compostable it needs to leave no toxic residue in the soil . It also needs to breakdown to a specific state within a certain timeframe which is less than 180 days . Biodegradable plastics can contain fillers, plasticisers and dyes which will affect the quality of compost, this is largely unresearched. A study by Scion and Agresearch is looking into whether compostable products certified by European Standard EN 13432 can be composted in New Zealand facilities with no negative effect on soil quality. The study is due to be finished in May 2021.
Figure 2, Diagram showing common plastics and biodegradable plastics and their correct disposal 
According to WasteMINZ  as of 2019 there are 19 commercial compost facilities in New Zealand that are accepting compostable packaging materials. However, these facilities will only accept materials that are certifiably biodegradable and/or compostable; usually under these standards; AS 4736, EN 13432 and ASTM D 6400 / 6868 .
Points to Highlight
- Overall there is a lot of R&D of new biodegradable materials, less R&D into their disposal and the flow-on effect to the environment and microflora and fauna.
- The variety (chemically) of biodegradable materials is diverse and each material has specific microorganisms that can break them down. This is a challenge for commercial composters.
- Biodegradable plastics, PCL, PGA and PBSA are derived from non-renewable resources just like common non-biodegradable plastics, PET and PP.
- New Zealand lacks collection point infrastructure to commercially compost. This is understandable due to the challenges to sort and decontaminate the plastics.
- Asking businesses and consumers to evaluate whether packaging materials comply to biodegradable and compostable plastic standards is a big ask, these materials need to be regulated.
Biodegradable plastics do have their merits in the sense that they degrade naturally into natural constituents. Non-biodegradable plastics tend to fragment into microplastics and take a long time to degrade if they do at all. In terms of the environment, the best option is to avoid single-use plastics altogether where possible.
 Rose Rattenbury (2021) Waste Disposal Options Wellington [Photograph]. Personal Cellphone
 WasteMINZ (2021) New Zealand facilities that accept compostable packaging and food [Photograph] https://www.wasteminz.org.nz/sector-groups/compost-nz/position-statement-from-new-zealand-composters-on-compostable-packaging/
 Yajie Zhong, Patrick Godwin, Yongcan Jin, Huining Xiao (2020). Biodegradable polymers and green-based antimicrobial packaging materials: A mini-review, Advanced Industrial and Engineering Polymer Research, Volume 3 (1) Pp (27-35) https://doi.org/10.1016/j.aiepr.2019.11.002
 Alger M. (2017) Polymer Science Dictionary. (3rd Edition). https://doi.org/10.1007/978-94-024-0893-5_2
 WasteMINZ. (2021). New Zealand facilities that accept compostable packaging and food. WasteMINZ. https://www.wasteminz.org.nz/sector-groups/compost-nz/new-zealand-facilities-that-accept-compostable-packaging-and-food-serviceware/
 Parliamentary Commissioner for the Environment (2018) Options for composting or recycling common plastics in New Zealand [Infographic]https://www.pce.parliament.nz/publications/biodegradable-and-compostable-plastics-in-the-environment
 Grant Northcott and Olga Pantos (2018). Biodegradation and Environmental Impact of Oxo-degradable and Polyhydroxyalkonate and Polylactic Acid Biodegradable Plastics. Parliamentary Commissioner for the Environment https://www.pce.parliament.nz/media/196536/oxo-and-biodegradable-plastics-report-northcott-and-pantos.pdf