Plastic has multiple uses nowadays, from kitchenware to bags for carrying vegetables. Unfortunately, plastic is also often found discarded outdoors. Whether intentionally or accidentally dropped as litter, or disposed of in waste water, residues of plastic contaminate our oceans, lakes and soil. What many of us may not realise though, is the fact that farmland is also impregnated with microplastics... via the compost used to fertilise crops.
The microplastics found in compost are no bigger than 5 mm in diameter and come mainly from food packaging and other items made from biodegradable resources, called ‘bioplastics’. The rapid development of green waste collection and the introduction of a bin bag tax in several Swiss cantons over recent years has led to an expansion in the range of ‘bio-based’ containers such as green waste bags, flower pots, toys and kitchen utensils. However, ‘bio-based’ does not necessarily mean biodegradable and these containers cannot always be thrown out with green waste.
On the one hand, bioplastics is a term used to describe plastic materials made from renewable resources, such as corn or sugar beet. They may be labelled ‘made from renewable resources’ or ‘bio-sourced’, but are likely to comprise other materials which are not necessarily biodegradable.
On the other hand, the term bioplastics also describes materials with certain degradation properties. Whether these materials are made from renewable substances (cellulose, sugar cane fibres, palm leaves, plant starch, etc.) or from non-renewable matter, i.e. fossil-based resources, they break down completely in the presence of microorganisms that transform them into water, carbon dioxide and biomass. Hence, they are deemed ‘biodegradable’ or ‘compostable’.
Unfortunately, the market is overflowing with so-called oxo-biodegradable plastics.1 These are similar in appearance to other plastics and break down into miniscule particles that are not readily biodegradable. This complexity is compounded by the recycled plastic bags sold in supermarkets. Contrary to popular belief, these recycled bags are not compostable.
To add to the confusion, the terms ‘biodegradable’ and ‘compostable’ are often used interchangeably. Yet, while a compostable product is biodegradable, a biodegradable product is not necessarily compostable. In fact, ‘biodegradable’ is a generic term meaning that, over time, bacteria will decompose the product. The term ‘compostable’ is more specific. It indicates that a product will decompose in the conditions provided by a compost heap, i.e. with oxygen, humidity and a specific temperature (60°C for large-scale compost facilities).
In order to make things clearer, compostable bags are now easily identified by the crisscross pattern printed on them. These bags are destined either for compost containers managed by processing plants, or for garden compost heaps. Labels have been developed to make the distinction easier: ‘OK compost’ certifies that the products will break down in industrial compost facilities, whereas ‘OK home compost’ indicates that they will decompose on a garden compost heap, but more slowly and not so readily, due to a lower temperature than in a composting plant.