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Place 06 · The North Pacific Garbage Patch · Chapter 4 of 7
How Long Does It Stay?
Dozens of posters say a plastic bottle lasts 450 years in the sea, but when two chemists went looking for the study behind that number, they could not find one.
About 15 minutes · 1 video · 1 live data chart · 2 quick activities
Start here
Think like a bathtub
How long something stays in the ocean is its residence time: the amount in the ocean divided by how fast it comes in (or leaves). By that sum, an average water molecule spends about 3,100 years in the ocean before it evaporates, and sodium from rivers stays about 55 million years; in the Southern Ocean you met deep water that takes about 1,000 years to finish its trip. Plastic is harder, because it never really leaves: it just gets smaller.
Watch this
See it move
TED-Ed — What really happens to the plastic you throw away. Four minutes following three plastic bottles on three very different journeys. Only one of them gets a happy ending, and it is not the one in the ocean.
While you watch, look for
- The different places a thrown-away plastic bottle can end up
- What sunlight and waves do to plastic in the ocean, and what they do not do
- Something you did not expect. Hold onto it.
The short version
Three things going on here
The sunlight
UV makes plastic brittle
Ultraviolet light in sunlight slowly breaks the long molecules that plastic is made of, so floating plastic fades, cracks and turns brittle: photodegradation. NOAA points out that plastic at the sunny, warm, wavy surface probably breaks down faster than plastic lying on the dark, cold seafloor. Some plastics even contain chemicals added to resist sunlight, which makes them last longer still.
The waves
Smaller, not gone
Waves, sand and heat crack brittle plastic into smaller fragments, and the fragments keep breaking into microplastics smaller than 5 mm, then smaller still: fragmentation. The pieces are still plastic, and NOAA says plastics of all types, even some labeled biodegradable, could stay in the ocean for an indefinite amount of time. In the 2015 survey of the patch, some objects were stamped with production dates from the 1970s and 1980s.
The mystery
Where did it all go?
Rivers alone are estimated to carry 0.8 to 2.7 million tonnes of plastic into the sea every year, yet all the plastic floating on the world’s ocean surface adds up to only a few hundred thousand tonnes. The rest is the “missing plastic”: much of it probably washes up and gets buried on shorelines, some sinks to the seafloor, and some is broken into pieces too small for the nets to catch. Nobody has a complete answer yet, which is a big part of Chapter 5.
Photos: Katia Nazarenko, Sébastien Vincon, Magda Ehlers / Pexels
Play with it
Watch the faucet open
In the bathtub model, residence time is the amount in the tub divided by how fast water flows in. This chart from Our World in Data shows how much plastic the whole world has made each year since 1950: hover along the line to read the numbers.
Interactive chart: Our World in Data, “Global plastics production,” from Geyer et al. (2017) and the OECD (2022).
Two questions to answer while you are in there
- About how much plastic did the world make in 1950, and about how much in 2019? How many times bigger is that?
- Think of the ocean as a bathtub for plastic: the faucet keeps opening wider and the drain is tiny, because plastic barely breaks down. What happens to the amount in the tub? Would the garbage patch vanish soon if the faucet were turned off tomorrow?
Try it yourself
Check yourself
Try it
How a Bottle Becomes Microplastic
Pick the one true statement in each set, and the life story of a lost plastic bottle builds itself.
Try it · interactive
Breakdown Clock
Pick an item (a bottle, a bag, fishing line, a foam cup and more), expose it to sunlight and waves, and watch it fragment into microplastics over its rough estimated lifetime; then fill a bathtub to see how residence time equals the amount divided by the inflow.
Open the Breakdown Clock in its own window (opens in a new tab).
Words you will hear
Four terms, that is all
Residence time
Average time something stays in a reservoir
Photodegradation
Breakdown of plastic by sunlight's ultraviolet light
Fragmentation
Breaking into smaller and smaller pieces
Persistence
How long something lasts in the environment
Check your understanding
Practice the whole chapter
Everything in this chapter, in eight quick questions. Retry as often as you like. Read the feedback on every answer, right or wrong, because that is where the learning is.
Practice
Practice: How Long Does It Stay?
Eight questions covering the video, the three cards, the four terms and the interactive above.
If you want more
Go deeper
- Our World Ocean 8.9 — Residence Time — LibreTexts · 5 minutes
- Oceanography 101 (MiraCosta) 17.11 — Solid Wastes — LibreTexts · 6 minutes
- NOAA Marine Debris Program — The Mystery of How Long Until It's Gone — NOAA · 4 minutes
Photo credits (Pexels): Francesco Ungaro, Erik Mclean, Katia Nazarenko, Sébastien Vincon, Magda Ehlers.
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