The oceans are polluted with tons of plastic. Floating garbage collectors, which fish off the plastic parts on the surface of the water, should offer a solution. Researchers have now investigated what they bring – with rather disappointing results. Because even if hundreds of such collectors were in use, they would only collect and remove a tiny fraction of all plastic waste in the ocean.
Huge amounts of plastic end up in the sea via coasts, ships and rivers. An estimated 5.25 trillion plastic particles swim on the surface of the water alone. The mass of the floating plastic is currently around 399,000 tons – this corresponds to the weight of around 4,000 blue whales. This plastic waste is an acute threat to the oceans: many marine life eat or swallow the plastic – often with fatal consequences. When plastic parts decompose, they release toxic additives such as plasticizers into the marine environment. These also reach humans via marine animals.
Basic cleaning of the seas?
Private initiatives like the Dutch “Ocean Cleanup” have developed a technology to rid the oceans of plastic. With the help of 600-meter-long floating barriers, floating garbage collectors are supposed to fish off plastic parts up to one millimeter in size that float on the water surface and remove them from the water. A ship transports the waste back to shore, where it is burned or recycled. “Ocean Cleanup” has set itself the goal of cleaning the “Pacific Garbage Patch” in the North Pacific – the largest garbage vortex in the oceans – within 20 years.
A research group led by Sönke Hohn from the Leibniz Center for Tropical Marine Research in Bremen has now examined how realistic this is. In their study, the scientists used mathematical models to analyze how effective the use of such garbage chutes would be. Using various scenarios, they compared the expected impact of the new technology on the amount of plastic waste in the ocean over the next 130 years – from 2020 to 2150. They prognosticated how the situation of the seas could develop without any cleaning, with the use of one or 200 plastic swallowers or with the help of floating river barriers. According to their calculations, a garbage chute moving at around 600 meters per hour can clean a sea surface of almost 2,700 square kilometers per year – this corresponds to 0.00073 percent of the total water surface of the oceans.
Only a fraction is removed
The model projections showed: Without the use of any technologies, the amount of surface plastic in the oceans is estimated to increase threefold within 40 years. If 200 rubbish chutes are used in the period up to 2150, however, the amount of plastic on the sea surface could be reduced by around 44,900 tons. That corresponds to a little more than five percent of the estimated global total by the end of this period. “In view of the huge amounts of plastic waste that continually pollutes the oceans, that is a rather small contribution,” says Hohn. Since the plastic swallowers can neither capture the microplastic nor fish the plastic parts that have sunk to the seabed out of the water, they only influence the plastic deposits on the water surface.
“Even if the marine plastic can be successfully collected, the question remains what happens to this plastic waste on land,” say the researchers. “Until now, most of the plastic that has been thrown away ends up in landfills, where it takes hundreds of years to decompose and in the process release toxins into the soil and groundwater.” It is difficult to recycle the plastics from the sea because the plastics are very different and often overgrown with microorganisms. Sorting would take a lot of effort. And when burning as an alternative, the high CO2 emissions pollute the atmosphere. “By giving the impression that they represent an effective solution to the problem of plastic in our oceans, these technologies can provide a justification for further pollution of the environment”, fears Hohn’s colleague Agostino Merico.
According to the scientists, the garbage collectors are meant to be nice, but not very effective: “Our results show that removing plastic from the ocean has only a negligible effect – if only because of the sheer size of the ocean’s surface and the enormous amounts it releases into the environment released plastic, ”they state. Only curbing the influx of plastic waste into the oceans can help. “There is only one solution: we have to stop the production of plastics and promote alternative, more sustainable solutions such as the use of biodegradable materials,” stresses Merico.
Source: Jacobs University Bremen; Technical article: Science of The Total Environment, doi: 10.1016 / j.scitotenv.2020.141115