We see the term ‘biodegradable’ on some products that we buy, such as washing powders and shampoo, but what does it actually mean?
The ‘degradable’ part of the word simply means that the product is able to break down into smaller compounds and eventually into very simple compounds such as carbon dioxide, water and oxygen.
The ‘bio’ part of the word means that the process is helped along with biological organisms, such as fungi and bacteria, which digest the material.
So a ‘biodegradable’ object is one that will break down quickly and safely into harmless compounds by using the action of microorganisms.
Composting is another name for biodegrading.
When a leaf falls off a tree onto the ground, it will rot away until nothing visible is left – this is biodegradation at work. Fungi and bacteria break up the leaf into smaller and smaller parts and eventually into carbon dioxide, oxygen and other important elements that have helped make up the leaf, such as phosphate and nitrogen. These simple elements are harmless in the environment and can actually be beneficial, as it enables the tree to get back some nutrients. This is why people often collect and compost their biodegradable waste and later, when the material has broken down, put it on to the garden to act as fertiliser.
So what makes a product ‘biodegradable’? Any material that comes from nature will be able to return to nature provided that it hasn’t been changed too much by man-made processing. For example, we all know that an apple core is capable of biodegrading even if we accidentally leave it in our school bag, but what about a T-shirt? A T-shirt is made from cotton, which is from a plant, but it has been processed by spinning the thread and weaving the cloth – but because it is still basically from a plant, it will break down, though not as quickly as it would had the fibre been left on the plant.
Nature of science
Science is often supported by observation. You can observe the biodegradability of dead organisms by leaving them and watching the fungi and bacteria break them down over time. The amount of degradation can also be measured by changes in the volume of the material over time.
Any plant-based, animal-based or natural mineral-based product has the capability to biodegrade, but they will biodegrade at different rates depending on the original material and how much it has been processed.
Products made from man-made compounds formulated in a laboratory are in combinations that do not exist in nature and therefore microorganisms are not able to break them down.
Find out how and innovative New Zealand company, Potatopak, use waste potato starch to make biodegradable disposable plates and trays.
Did you know that the rate at which biological material degrades is dependent on conditions such as light, water and temperature and the types or microorganisms present, as well as the type of substance, find out more about measuring biodegradability.
Use this activity with your students and set up an experiment to determine the biodegradability of different substances.
Find out more about backyard composting on this website.