About 8.8 million tonnes of plastic are accumulated in the oceans each year, but it is estimated that only about 270,000 tonnes float on the surface of the ocean.
For years, most scientists believe that the "missing" plastic quickly decomposes upon entering the ocean, breaking into microplastics – small fragments of less than 5 millimeters in length. Many small researchers then fall to the bottom of the sea.
But this theory is at odds with observations made by non-profit researchers at The Ocean Cleanup, which aims to free the oceans from plastic. The organization was founded in 201
Read more: The massive plastic cleaning device invented by a 25-year-old can finally throw garbage into the Great Pacific Garbage. Look at her difficult path.
On Thursday, The Ocean Cleanup released a study that offers an alternative explanation for why certain plastic objects sit on the surface of the water while others disappear. Instead of dissolving rapidly in microplastics, the team found that plastic objects were repeatedly pushed back to the land or disappeared below the surface of the water.
"That's quite the opposite opinion," Slat told Business Insider. "I think we have been able to address, or at least hint at, the biggest gap in plastic pollution knowledge."
"We really don't find any plastic bags or straws"
Over the last few years, Ocean Cleanup researchers have noticed that a specific type of plastic is accumulating in the garbage patch.
"A lot of them are really tired and broken and some of them look really old," says Laurent LeBreton, lead author of the study at Business Insider. "We don't actually find any plastic bags or straws, but we do find really thick, solid plastic fragments."
Most of the objects extracted from the garbage patch in 2015 have been discovered by researchers since the 2000s. Some were much older.
This suggests that plastic objects do not disintegrate very quickly.
"It's really shocking to see pieces of plastic still floating there that are from the 70s," Slat said. "Just a few weeks ago, we restored a crate that has literally been in Japan since 1970."
Researchers have come to the conclusion that, instead of being destroyed, plastic objects go on a long journey, sometimes traveling for decades before accumulating in large offshore spots.
The voyage of plastic across the ocean
A small proportion of plastic in the ocean comes from the illegal dumping, spilling of the sea or production facilities that dump plastic waste into nearby waterways. But most of it comes from landfall.
Plastic waste entering the ocean is sometimes accumulated along coastlines where there are no people to collect garbage. An example of this, Lebreton said, are the Cocos Islands in Australia – a remote area with few inhabitants that has the highest density of plastic debris recorded worldwide (about 260 tonnes). On these shores, a large amount of plastic is discharged from the tide and then transported back to the same place.
This cycle ends with the degradation of the plastic or the passage into the offshore.
Less than 1% of the plastic that enters the ocean from shore actually makes its way to fat like the Great Pacific garbage, researchers have found.
As a plastic object travels across the ocean, organisms such as algae or jars attach to it and begin to weigh it – a process known as "decay". The object then sinks beneath the surface of the water to deeper parts of the ocean.
Algae and barrels need sunlight to survive, and this becomes scarce when they sink deeper into their plastic home. Ultimately, organisms can die and fall from the plastic object, allowing it to rise back to the surface of the water.
Lebreton said that thick pieces of plastic often withstand the weight of organisms, while thin pieces tend to lose their buoyancy. That explains why there aren't many thin straws or nylon bags in the trash can, he said. Researchers have found that thin pieces of plastic can spring back to the surface in deep water, but in shallower waters, they are more likely to land at the bottom of the ocean and stay there.
Cleaning up the Great Pacific Garbage
In the end, the plastic that winds up swirling in offshore vortices deteriorates, but it may take some time. Researchers have found that most plastic objects that are currently being disintegrated in microplastics were manufactured in the 1990s or earlier. When a plastic object breaks down, the resulting microplastics tend to drift ash to the bottom of the ocean.
Lebreton said that the garbage in the Great Pacific garbage can take several decades, if not centuries, without intervention.
"If you stopped putting plastic in the ocean or just in the natural environment as a whole, you will still have to deal with the legacy of plastic waste," he said. "In that sense, we can really say that the worst is yet to come."
Slat says the new study "validates Ocean Cleanup's strategy" because addressing the problem of plastic pollution requires both prevention (such as recycling) of earth's effort) and cleaning the plastic that is already in the water.
The Slat solution is a floating U-shaped array that traps plastic in its fold as a giant hand. The device moves slower than the ocean thanks to an underwater parachute that serves as an anchor. While natural winds and waves push plastic toward the center of the U-shaped system, debris is captured by a screen that extends below the ocean's surface. The collected garbage can then be towed ashore.
If successful, the Ocean Cleanup project says its device can reduce the size of the garbage patch by half in five years.
"It's not really a question for me if it will work, but when it will work," Slat said. "I don't think we have a choice given the scale of the problem."