“Biodegradable” has become one of the most reassuring words in modern packaging. It appears on coffee cups, shopping bags and food containers, implying a promise: this product is better for the environment because nature will eventually take care of it.
However, biodegradability is not a simple yes-or-no property. It exists in shades, which we can measure.
Biodegradation is a complex process. Microbes and molecules present in an environment such as soil attack a material and digest it, much like what happens to food in our gut.
A material is typically defined as biodegradable if it is digested “well” by the environment in which it is placed. The more mass the material loses during digestion, and the more carbon dioxide it produces, the more biodegradable it is.
Different environments digest materials in different ways. Temperature, sunlight, oxygen, moisture and microbial diversity all influence how quickly materials degrade.
Even the most rigorous testing cannot fully capture the complexity of the real world – but it can help guide our choices.
Biodegradability is relative
In the lab we can simulate environments such as landfill, home compost bins and industrial compost facilities. If we understand in which settings a material breaks down better, we can tell the consumer how to best dispose of it and prevent pollution and other issues.
A material that decomposes quickly in an industrial composting facility may persist for years in the ocean or landfill.
Industrial composting systems maintain elevated temperatures, controlled aeration and consistent moisture. Hot, moist and oxygen-rich conditions generally aid biodegradation but they are not easy to come by in a backyard compost bin.
Home compost systems are typically cooler and more variable. The result: a material certified for industrial composting may not break down effectively at home.
Take polylactic acid (PLA), a biodegradable material generally considered to be a greener alternative to common plastics (like PET). PLA can biodegrade effectively in an industrial composting system. With temperatures above 60°C and controlled moisture, oxygen and microbial activity, microbes can convert PLA into carbon dioxide, water and biomass in just a few days.
Outside these conditions, the story changes. If PLA ends up in landfill, decomposition can be slow because oxygen is limited. In rivers or marine environments, it may persist for years and act as a raft for “alien” species. In your compost bin or worm farm it might disappear in a few months.
Time for standards
There are many ways to measure biodegradability. One common series of tests, OECD 301 assesses “ready biodegradability” in different environments as a material’s ability to biodegrade around 60% within 28 days under controlled conditions.
Industrially compostable materials are tested under very specific conditions. Standards such as EN 13432, used in Europe, assess whether packaging can successfully break down in industrial composting facilities.
To meet the standard, at least 90% of the material must biodegrade into carbon dioxide, water and biomass within six months. These tests typically involve elevated temperatures, controlled aeration, and moisture.
Most biodegradable plastic materials do not disappear cleanly. Instead, they fragment into progressively smaller particles before fully breaking down. During this period, the fragments will continue interacting with organisms and ecosystems.
Compost bins too can get indigestion
Biodegradability standards are helpful for consumers and waste regulators. Nevertheless, they are limited. They often do not test how much of any given material a specific disposal system can sustain at any one time.
This is an important parameter to take into account. Take food waste. When large quantities of food lie in landfill without oxygen, they generate methane, a greenhouse gas far more potent than carbon dioxide over short timescales.
Other biodegradable materials are no different and can throw out the balance of an ecosystem such as your compost bin, if added in excessive quantities.
Introducing certain materials to a compost bin might also cause certain microbes to thrive and others to suffer, sometimes with unintended consequences, such as making your compost bin smell bad.
In the future, biodegradability tests will likely be paired with ecotoxicity assessments, to help us understand whether a material breaks down safely and without generating harmful byproducts or microbial imbalances.
What can we do?
Few of us have an industrial composting facility nearby to take care of biodegradable materials. Industrially compostable products such as coffee cups often end up sent to landfill alongside conventional waste.
This does not mean individuals are powerless or that biodegradable materials are inherently bad.
You can start by checking local council guidance and choosing products certified for the systems available in your area, or your compost bin.
Ask yourself:
is this product home compostable or only industrially compostable?
is there infrastructure locally that can process it?
has it been independently certified?
As for industrially compostable coffee cups, check that you can return cups to participating cafes. They should not be placed in standard recycling bins or food and organics bins as they are considered contaminants. If unsure, place them in a bin destined for landfill.
Ultimately, the most sustainable option remains a reusable washable cup.
These may seem like small actions but they help push packaging design and waste systems toward greater transparency and accountability.
Moving beyond simple labels
As consumers, we want to make educated choices about their purchases and how they can be disposed of.
For now, we have simple labels. In the future, we will hopefully have more complete information about how materials degrade in industrial composting facilities, home compost bins, soil, freshwater, sea water and landfill sites.
Biodegradable materials offer clear advantages over highly persistent materials, but the term “biodegradable” should not be mistaken for environmentally harmless.
Let’s just remember that a biodegradable material released in the wrong place, at the wrong scale, or under the wrong conditions may behave not very differently from a non-biodegradable material.
Understanding the shades of biodegradability moves the conversation beyond simplistic labels. Nature can break many things down, eventually. The more important question is whether it can do so without getting indigestion.
Martin Zaki, Associate Research Fellow in Biomaterials, Deakin University and Alessandra Sutti, Associate Professor, Institute for Frontier Materials, Deakin University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
