Over the past seven years, the concentration of plastic fragments in the North Pacific garbage patch has increased fivefold. This pollution does not only come from the degradation of the waste already present, but also from a massive external input. We take a closer look at a phenomenon with major ecological consequences and the methods used to measure it.
By Laurie HENRY
The Great Pacific Garbage Patch (GPGP) is the largest of the five areas of plastic waste accumulation in all the world’s oceans. It forms in the heart of the North Pacific subtropical gyre, a gigantic oceanic loop created by the Earth’s rotation and prevailing winds. This vortex phenomenon, present in every ocean, traps plastic waste in a circular motion, preventing it from dispersing. In addition to the GPGP, other similar gyres exist in the North and South Atlantic, the South Pacific and the Indian Ocean, each harbouring a vortex of waste. These areas retain plastics for decades, promoting persistent pollution and seriously threatening marine biodiversity.
Pollution is sharply on the increase
A study, published in November 2024 in Environmental Research Letters and conducted by Laurent Lebreton and his colleagues from The Ocean Cleanup, quantified the evolution of plastic pollution in the North Pacific garbage vortex between 2015 and 2022.
The analysis revealed a drastic increase in the concentration of floating plastic fragments. In just seven years, the total mass of these fragments has increased from 2.9 kg to 14.2 kg per km², a near five-fold increase. The concentration of microplastics (0.5 to 5 mm) has increased dramatically, from 960,000 to 1.5 million particles per km², while that of mesoplastics (5 to 50 mm) has jumped from 34,000 to 235,000 particles per km².
Map showing surveillance efforts in the GPGP from 2015 to 2022. © L. Lebreton et al., 2024In some of the worst affected areas, the situation is even more alarming. In 2015, researchers had identified concentrations of small particles reaching 1 million particles per km² in the worst accumulation areas. Seven years later, these figures have increased tenfold, exceeding 10 million particles per km². Such an increase is indicative of a rapid and uncontrolled accumulation dynamic, making plastic pollution increasingly difficult to manage.
Observations combined with digital models
To achieve these results, the Ocean Cleanup team combined direct observations at sea with mathematical modelling. Between 2015 and 2022, the scientists organised fifty expeditions across the GPGP accumulation zone. During these campaigns, they used different tools to sample plastics of all sizes: Manta trawl nets to capture microplastics and mesoplastics, Mega trawl nets for larger waste items, as well as aerial overflights to detect megaplastic on a large scale. The Ocean Cleanup’s cleaning devices were also used to extract and examine the waste recovered in certain specific areas of the gyre.
All this data was then analysed using a mass balance model aimed at understanding the origin of this pollution. This model made it possible to assess whether the fragmentation of the waste already present could alone explain the observed increase, or whether other sources of pollution were involved. The researchers thus incorporated parameters such as the rate of degradation of plastics at sea, estimated at between 1% and 3% per year under the effect of UV rays and sea currents, as well as the quantity of new waste entering the area.
The results are clear: the majority of the fragments found in 2022 do not come from the degradation of the plastics already present, but rather from external sources. According to researchers’ estimates, between 74% and 96% of these microplastics come from waste carried by ocean currents, after being released into the environment from rivers and coasts sometimes located thousands of kilometres from the GPGP.
Worrying ecological consequences
This explosion in the number of plastic fragments is having a considerable impact on marine ecosystems. Ocean fauna is the first to be affected. More than 900 species are now affected by plastic pollution, including around 100 classified as endangered. Seabirds, fish and turtles ingest these microplastics, mistaking them for plankton, which disrupts their digestion and metabolism. In the long term, this ingestion can cause serious toxic effects and weaken certain animal populations that are already vulnerable.
Change in concentrations of floating microplastics (0.5–5 mm) in the most polluted areas of the GPGP between 2015 and 2022. The symbol ∗ indicates a significant variation compared to 2015. © L. Lebreton et al., 2024
Beyond the direct impact on wildlife, this pollution is profoundly changing ocean ecosystems. Opportunistic species, transported by floating waste, are colonising new areas and entering into competition with species endemic to the Pacific. This forced redistribution of biodiversity could throw certain food chains out of balance and alter the structure of local ecosystems.
This pollution could also disrupt the carbon cycle. Zooplankton, which plays a key role in the absorption of atmospheric carbon dioxide, finds its grazing activity hampered by the massive presence of plastics in suspension. This interaction could have repercussions on the oceans’ ability to regulate the climate, making the need for rapid intervention even more pressing.
Laurent Lebreton, the study’s lead author, warns: “The exponential increase in plastic fragments is a direct consequence of decades of poor waste management. This phenomenon is causing damage the scale of which we are only just beginning to grasp.’
A global problem requiring urgent action
Faced with this growing ecological crisis, researchers are calling for coordinated action at the international level. The priority remains to limit the production and use of single-use plastics, while improving waste management infrastructures to prevent them from leaking into the environment. At the same time, intercepting plastic waste in rivers is an effective strategy for preventing it from reaching the oceans, as demonstrated by the initiatives of The Ocean Cleanup.
But efforts must not be limited to prevention. Cleaning up accumulation zones remains essential to limit the fragmentation of already present waste and reduce its effects on marine ecosystems. As such, collection operations at sea must be intensified and supported in the long term.
The study emphasises that without rapid intervention, the concentration of plastic fragments in the GPGP will continue to increase, making their elimination increasingly complex. Laurent Lebreton concludes: ‘Our results should be a wake-up call to accelerate the implementation of a global treaty against plastic pollution’. This binding treaty, currently under discussion at the United Nations, could mark a decisive turning point in this fight. The urgency is real: the decisions made today will determine the state of the oceans for decades to come.
Source : L. Lebreton et al., “Seven years into the North Pacific Garbage Patch: legacy plastic fragments rising disproportionally faster than larger floating objects”, Environmental Research Letters (2024).