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Plastic waste in the sea stems mainly from fishing

A large proportion of the litter that has accumulated in the subtropical vortex of the North Pacific Ocean between California and Hawaii in the so-called "Great Pacific Garbage Patch" (GPGP) originates, according to a recent study, directly at sea and is caused by very few countries. According to the study, which has been published in “Scientific Reports” by a research group from the Dutch non-profit organisation “The Ocean Cleanup”, the garbage vortex contains mostly fishing nets, ropes and other waste from industrial fishing.


The Ocean Cleanup is a Dutch non-profit organisation that develops and deploys technologies at sea to rid the oceans of plastic waste. As part of a series of tests on a cleaning-up system, The Ocean Cleanup collected plastic waste from the North Pacific garbage patch in 2019. Immediately after recovery, the collected waste was divided into two fractions: Firstly, hard plastics (i.e. rigid objects) and secondly, nets and ropes.


A team led by research leader Laurent Lebreton analysed the finds for the study, which was supplemented by model simulations as well as findings from a previous oceanographic mission, focusing on the hard plastic pieces. The hard plastic fraction was first sorted individually into 112 predefined categories from nine different material types. This was based on the OSPAR Convention, which also monitors beach litter within its monitoring programme. This was to make the results comparable with data on beach cleaning activities. Both intact items and fragments that could be identified as belonging to a certain item category, such as parts of a box, were then assigned accordingly. The items were each examined individually for indications of country of origin, such as language, company name, trademark, logo, other text, etc. Two-thirds of the marine litter had consistent characteristics, allowing the researchers to assign them to a category. In the case of the rest, the hard plastic pieces had been so badly decomposed by the sun and salt water that it was no longer possible to identify what they were or where they came from.


According to the analysis, of the items found that could be identified, fishing nets and fishing gear for aquaculture accounted for 26 percent of the plastic items collected and 8 percent of the mass, while plastic floats and buoys accounted for 3 percent with 21 percent of the total mass. Plastic items associated with food and beverages accounted for 13 percent of the total plastic items and consisted mainly of bottle caps and lids. Due to their light weight, they therefore accounted for only 1 percent of the total mass. Finally, household items accounted for 14 percent of the number of plastic items and 16 percent of the mass.


On more than 200 of the pieces of plastic, the research team identified writing in a specific language. The study found that Chinese and Japanese were among the most common languages, followed by English and Korean. On a total of 232 pieces of plastic, the team was able to determine the origin based on language, text, company name or logo. For other items that were found, the research team could not determine the origin, for example, because the company that was identified on the piece of litter has international production facilities. Finally, the team determined the five countries of origin from which most of the collected plastic waste in the North Pacific garbage vortex originated: Japan, China, Korea, the U.S. and Taiwan - confirming findings from earlier studies in 2015. According to the analysis, around two-thirds of the litter stemmed from either Japan (34 percent) or China (32 percent). The rest came from Korea (10 percent), the U.S. (7 percent) and Taiwan (6 percent).


To track how and where the plastics entered the ocean, the scientists used dispersion simulations of the transport of floating marine debris, which they compared with their analysis of the composition of the plastic litter from the North Pacific garbage vortex. As a result, they concluded that it was highly likely that most of it had not entered the ocean via rivers or coastal cities, but rather directly through fishing activities. The researchers' calculations showed that a plastic fragment that ended up in the vortex was ten times more likely to be associated with fishing activities than with activities on land. They showed that up to 86 percent of the plastic fragments analysed from the vortex are lost from fishing vessels, or are left behind by the seamen or intentionally discarded by them.


According to Lebreton and his team, the study shows that most of the floating plastic in the subtropical vortex of the North Pacific can be traced to five industrialised fishing nations, in contrast to recent assessments of plastic discharges into the ocean, which point to developing coastal countries and rivers as the main contributors to plastic pollution. The fishing industry thus has an important role to play in the fight against plastic waste pollution in the oceans, according to the scientists. "To stop the influx of plastic into our oceans, addressing emissions from rivers - the largest source - must be a top priority," said Boyan Slat, founder and CEO of The Ocean Cleanup. "However, to ensure that our work to clean up the Great Pacific Garbage Patch is truly sustainable, the throwing away of fishing gear must also be stopped. We hope our latest study will empower organisations and the fishing industry itself to address this other source of plastic pollution in the GPGP."



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