How Long Plastic Takes To Break Down & Degrade (In Landfills, In The Ocean & The Environment)

How Long Plastic Takes To Break Down & Degrade (In Landfills, In The Ocean & The Environment)

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

* 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]

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