An ambitious yet straightforward method of ridding the oceans of huge swaths of accumulated plastic began on 18 October with the deployment of a drifting U-shaped tube at the Great Pacific Garbage Patch, midway between Hawaii and California. The Ocean Cleanup aims to remove 50% of the patch’s plastic within five years, and 90% of the plastic in all the world’s oceans by 2040.
Rotating currents have collected plastic into five huge ocean gyres around the globe. Early this year, scientists collaborating with the Ocean Cleanup estimated that the North Pacific gyre—the site of the Great Pacific Garbage Patch—harbors some 79 000 metric tons of extractable plastic. Marine life can get caught and killed in nets and other holey or twisty plastic trash. Heavy metals and persistent organic chemicals from plastics enter the food chain.
The Ocean Cleanup approach takes advantage of the same factors that aggregate the plastic waste to begin with: winds, waves, and currents. A 600-meter-long tube made of high-density polyethylene bobs at the ocean’s surface. Held by rope in a flexible U shape, the 1.2-meter-diameter tube has a skirt that extends 3 meters into the water. Currents propel the tube and the plastic waste similarly. But the tube at the surface is acted on more by the wind and waves than the plastic garbage, which is mostly just below the surface. As a result, the garbage accumulates at the tube’s skirt.
The idea is to mimic nature, says Laurent Lebreton, the Ocean Cleanup’s lead oceanographer. “The system moves the way the plastic moves. It reproduces a false coastline, where the garbage gathers. We can then collect it.” Periodically a ship will come haul out the garbage and make room for more. Meeting the five-year goal will require a fleet of 60 systems like the one launched last month.
The passive garbage sweep is fitted with solar-powered lights, cameras, sensors, and satellite antennas. The sensors communicate data on position, conditions, and performance. People currently keep tabs on the system on-site, but eventually it will be monitored only remotely. The system continuously broadcasts its location to passing vessels.
The Ocean Cleanup is the brainchild of Boyan Slat of the Netherlands. While on a dive in Greece at age 16, he came across more plastic than fish. That led to a high school project on marine pollution. He stayed with the topic, eventually dropping out of college to focus on cleaning the oceans.
The nonprofit Slat founded in 2013 now employs roughly 80 engineers, scientists, and environmentalists, who also work with university partners. For the past several years, the Ocean Cleanup team has tested and refined the system using modeling and experiments. For example, they collected samples to measure the depths at which plastic accumulates and found that it tapers off significantly below 3 meters. If the waters are calm, the debris stays close to the surface, Lebreton says.
Pinpointing the location of plastic is a challenge, says Shungudzemwoyo Garaba of the University of Oldenburg, Germany, who consults for the Ocean Cleanup. “We know more or less where it is, but the stuff is always moving. That’s where remote sensing comes in.” By flying imaging instruments over water, Garaba and colleagues demonstrated that plastics possess uniquely identifying spectral characteristics in the infrared. “We can robustly distinguish” plastics at the ocean surface from algae and other vegetation that contain hydrocarbons, Garaba says. The method works with airborne imaging, and early results with satellites are promising, he adds.
Over time, the plastics break down into ever-smaller pieces. The Ocean Cleanup is focusing on debris 1 cm and larger. Smaller microplastics are more likely to sink deeper and are harder to gather. “Some 92% of the total plastic mass present in the Great Pacific Garbage Patch is carried by larger pieces, so we will pick that up first,” says Lebreton. The buoyant plastic that accumulates in the ocean is mostly made of polyethylene and polypropylene, he says.
In the longer run, the team hopes to sell its haul for recycling. Plastic can be mechanically and thermally downcycled into other products, burned, or chemically or biologically treated, says Lebreton.
Research and development have totaled about €20 million ($23 million) to date, including €4.4 million for the first sweeper. The cost is expected to decrease as the project scales up. The Ocean Cleanup got started with a crowdfunding campaign and now has major donors.
