It is quite common for people to believe what they are told – especially when a piece of information comes from a trusted source, such as the news or a reliable brand.
It takes plastic bags around 500 years to biodegrade, but plastic bags have only been around for the past 50 years, how do we know how long it will take for them to complete this process?
In order to make such assessments, scientists must conduct respirometry tests that measure the rate of carbon dioxide production or oxygen consumption of an organism or organic system.
To do this, researchers take a solid waste sample and place it in a container with microorganisms and soil. The container is then aerated (supplied with oxygen or air) and over the course of several days, the microorganisms interact and consume the sample – creating carbon dioxide in return.
The scientists then measure the biodegradability of a sample based on how much carbon dioxide is produced during a set time period.
But this doesn’t work for everything
Although organic matter is measured using respirometry, plastic bags and other man-made materials cannot be tested in this way – as microorganisms do not eat things such as polyethylene.
So how are man-made materials tested?
Although materials such as polyethylene bags don’t biodegrade, they do do something called photodegrading.
When exposed to ultraviolet radiation from sunlight, the polymer chains within polyethylene become brittle and start to crack – suggesting that the bags will eventually break down into ever smaller granules.
The truth however, is that scientists don’t quite know how long it takes for this to happen – with some scientists offering 500 years as the answer, while some suggest a more conservative 1,000 years.
It is also estimated that it might take glass around one million years to fully biodegrade, but we won’t be able to find that out for a very long time.
How are non-biodegradable products dangerous?
The basic issue with non-biodegradable materials is that they can last for centuries and can affect a variety of environments.
Marine life tends to suffer a great deal because of non-biodegradable products. Fish, seabirds and other marine life may become entangled, or swallow dangerous materials that they cannot digest.
Microbeads are especially dangerous to wildlife as they are too small to be captured by water treatment facilities. The New Democrats in Canada are currently trying to classify microbeads as a potentially toxic substance.
On land, non-biodegradable items can still affect animals, with materials such as Styrofoam making their way into fields, forests, parks and eventually into rivers and the sea. Polystyrene itself is especially dangerous as styrene is a neurotoxin that can bleed out of polystyrene in particularly warm weather.
How long does it take for materials to biodegrade?
As you probably know, different materials take different lengths of time to biodegrade completely, and this can vary from a matter of weeks up until nearly forever.
Take a look at the following table to see just how long it takes for different materials to biodegrade completely according to the U.S. National Park Service:
|
Material |
Time to biodegrade |
| Paper | Two to four weeks |
| Orange/Banana peel | Two to five weeks |
| Newspaper | Six weeks |
| Apple core | Two months |
| Waxed milk carton | Three months |
| Plywood | One to three years |
| Wool | One to Five years |
| Cigarette butt | One to Five years |
| Plastic film container | 20 to 30 years |
| Nylon | 30 to 40 years |
| Leather | 50 years |
| Tin can | 50 years |
| Rubber | 50 to 80 years |
| Foamed plastic | 50 years |
| Aluminium | 80 to 200 years |
| Disposable nappies | 450 years |
| Plastic bottles | 450 years |
| Monofilament fishing line | 600 years |
| Glass | One million years |
