Legos could last a disturbingly long time in the ocean

They likely survive many centuries — and other plastics may, too

By matching Legos weathered for decades at sea (pictured) to pristine versions of the same blocks, scientists estimate that it could take 100 to 1,300 years for some of these toys to break down in the ocean.

A. Turner/University of Plymouth

Ever stepped on a Lego? Then you know how hard and strong these plastic building blocks are. Now, scientists have discovered another unpleasant trait of these toys being so rugged: A single Lego could take hundreds of years to break down in the ocean.  

Earth’s oceans are littered with plastic of all types. But gauging how long that trash will take to break down in the seas has not been easy. One reason: It’s hard to date debris when you don’t know where it came from. One bit of broken plastic may look similar to another. But not Legos. It’s fairly easy to identify one of these blocks. Their shape is quite distinct, notes Andrew Turner. He’s an environmental scientist who works at the University of Plymouth. That’s in England. And because the chemical recipes used to make Legos have changed over time, each brick contains clues to when it was made.

Turner was part of a team that analyzed washed-up Lego blocks. Each of them had been collected since 2010 by beach-cleanup crews in Cornwall, England. The scientists used X-rays to identify the chemical recipe of each block. Shining such high-energy radiation on each Lego block caused atoms in the block to give off X-rays. By measuring the energies of those X-rays, the researchers could figure out what types of atoms were in the block. This technique offers what is basically a chemical fingerprint of a material. And such analyses showed the beached blocks were made of a recipe used around the 1970s.

One key ingredient had been cadmium. Lego makers had used it for the bright yellow and red pigments in blocks made from the early 1970s until the early 1980s. Later, this element was phased out over concern about how toxic it is.

The researchers assumed the Legos had been lost to sea shortly after they had been bought. They attempted to gauge how worn down these blocks had become during 30 to 40 years at sea. Likely wear would come from such things as exposure to sunlight and a sandpaper-like rubbing against sediment. To figure out how much the blocks had worn down, the researchers compared them to versions of the same blocks that collectors had held since the 1970s. They matched the beached blocks to those in the collections using those chemical fingerprints.

The scientists ended up with 14 pairs of matching Legos. The beached versions had 3 to 40 percent less mass than the mint-condition blocks did. That suggests it would take between 100 and 1,300 years to completely break down a single Lego block. Turner’s team is reporting its finding in the July 2020 Environmental Pollution.

Earlier work by others had shown that plastic water bottles take decades to break down in the ocean. But the plastic parts in electronics and many other products are closer in thickness and sturdiness to Lego bricks. That’s why Turner’s team now suspects a several-hundred-year timescale may better predict the likely breakdown rate of most plastics in the oceans.

Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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