Different types of plastic, and different plastic items and products can take different lengths of time to break down and degrade.
The conditions in which plastic are subject to can also have some bearing on this amount of time.
In this guide, we outline the different plastic types and products, and how long they might take to break down in different conditions.
Summary – Plastic, Breaking Down, & Degradation
Only some plastics are designed to break down as waste
Many plastics are non-degradable – which explains why some plastics made decades ago still exist as plastic waste today
If plastics don’t degrade, they simply break down into smaller and smaller plastic particles like micro and nano plastics (which can be ingested by wildlife amongst other things).
That, or bigger bits of plastic are ingested by wildlife, or entangle them
Plastics usually break down in either landfills, or the ocean (or other land or water based sources)
The conditions of the area that plastic waste resides in determines how, and how quickly it might break down
The ocean’s unique conditions though mean that plastics usually break down quicker here than when in landfill (where there may be a lack of light and physical weathering for example) – although some sources contradict this
UV (from the Sun) and physical weathering (from water, physical objects, and so on) are key factors that break plastic down
There are more recent and developing plastics such as bio plastics that can break down quicker than petroleum based plastics under the right conditions
Different plastic items have different estimated times to break down into microplastics – for example, a plastic bag might be 20 years, whilst fishing line may be 500+ years
* The numbers in the guide below are estimates.
How Different Plastics Break Down
We can see that different plastics and different conditions impact how plastics break down:
[most fossil fuel based plastic does not biodegrade like organic matter i.e. it does not break down via bacteria]
[most fossil fuel based plastics break down via photodegradation]
[however, there are two more common types of biodegradable plastic out at the moment -] plant-based hydro-biodegradable plastic and petroleum-based oxo-biodegradable plastic
polylactic acid (PLA), a plastic made from corn … decomposes into water and carbon dioxide in 47 to 90 days — four times faster than a PET-based bag floating in the ocean. But conditions have to be just right to achieve these kinds of results. PLA breaks down most efficiently in commercial composting facilities at high temperatures. When buried in a landfill, a plastic bag made from corn may remain intact just as long as a plastic bag made from oil or natural gas.
– science.howstuffworks.com
Note the difference between the phrase ‘degrade’ which means to simply break down, and ‘biodegrade’, which more commonly refers to the break down of material organically or naturally.
Reasons For The Break Down Or Degradation Of Plastic
The type of plastic or plastic product impact the rate of degradation
Consistent mechanical abrasion
Materials can slowly break down through photodegradation [through exposure to UV radiation] (ourworldindata.org). This breaks the bonds in the plastic material (science.howstuffworks.com)
Saline environments
Cool or warm environments [warm ocean water can speed up the break down of plastic – science.howstuffworks.com]
Rain and other environmental conditions
Ocean vs Landfill Break Down Rates
Ourworldindata.org suggests that the marine environment has factors which lead to quicker breakdown of plastic:
It’s important to note that within the marine environment, plastics can more readily break down into smaller particles: exposure to ultraviolet (UV) radiation, and consistent mechanical abrasion from wave action can cause larger particles to break down.
Wikipedia.org has some conflicting information on ocean break down rates:
Polymer degradation takes much longer as a result of saline environments and the cooling effect of the sea. These factors contribute to the persistence of plastic debris in certain environments.
Recent studies have shown that plastics in the ocean decompose faster than was once thought, due to exposure to sun, rain, and other environmental conditions
How Long Plastic Takes To Break Down & Degrade In Landfills
The rate of decomposition can be dependent on landfill conditions – each landfill can have different conditions.
Normally, plastic items can take up to 1000 years to decompose in landfills.
… plastic bags we use in our everyday life take 10-1000 years to decompose
… plastic bottles can take 450 years or more
… disposable diapers take approximately 250-500 years to decompose in landfills
Foamed Plastic Cups [can take up to] 50 years
– thebalancesmb.com
How Long Plastic Takes To Break Down In The Ocean, Or The Environment
The average estimated decomposition times of typical [plastic] marine debris items [are]:
Fishing line – 600 years
Disposable diaper – 450 years
Plastic bottle – 450 years
Plastic beverage holder (6 rings) – 400 years
Foamed buoy – 50 years
Styrofoam cup – 50 years
Plastic bag – 20 years
– ourworldindata.org
The lifecycle of plastics in the ocean are:
Plastic toothbrush – 500 years
Disposable diaper (need to be exposed to oxygen and sunlight in order to decompose, and they don’t decompose well in landfill) – 500 years
Coffee pod – 500 years
Plastic cup – 450 years
Plastic water bottle – 450 years
6 pack plastic rings – 400 years
Plastic straw – 200 years
Coffee cup (plastic liner on the inside) – 30 years
Plastic bag – 20 years
– wwf.org.au
Estimated time taken to biodegrade (in years):
Fishing line – 600 years
6 pack beer holder – 450 years
Plastic bottles – 450 years
Nappy – 450 years
Straw – 200 years
Foamed plastic cup – 50 years
– telegraph.co.uk (citing NOAA/Woods Hole Sea Grant)
How Long Plastic Bags Take To Break Down
From the above estimates, anywhere from 20 years in the ocean, up to 1000 years in landfill.
How Long Plastic Bottles Take To Break Down
From the above estimates, 450 years.
How Long Plastic Straws Take To Break Down
From the above estimates, 200 years.
Sources
1. https://ourworldindata.org/faq-on-plastics#how-long-does-it-take-plastics-to-break-down
2. https://www.thebalancesmb.com/how-long-does-it-take-garbage-to-decompose-2878033
3. https://www.wwf.org.au/news/blogs/the-lifecycle-of-plastics#gs.1mtftu
4. https://www.telegraph.co.uk/news/2018/01/10/stark-truth-long-plastic-footprint-will-last-planet/
5. https://en.wikipedia.org/wiki/Plastic#Decomposition_of_plastics
6. https://science.howstuffworks.com/science-vs-myth/everyday-myths/how-long-does-it-take-for-plastics-to-biodegrade.htm
7. Hannah Ritchie and Max Roser (2019) – “Plastic Pollution”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/plastic-pollution’ [Online Resource]
