- New research shows that the drift of microplastics from the Mekong River to the coastlines of countries around the South China Sea depends on variable factors, including seasonal changes in winds and ocean currents.
- The Philippines is most exposed to plastic waste that mainly drifts from the Mekong River to the sea during the monsoon season, with 47% of the stranded particles ending up on its coast, followed by Indonesia at 24%, Vietnam at 17%, and Malaysia at 8%.
- Environmental advocates say the findings of this study underscore the importance of international cooperation in combating plastic pollution, which harms marine biodiversity and coastal economies.
The marine biodiversity hotspot known as the Coral Triangle is home to more than 76% of the world’s known coral species and more than 3,000 species of fish. It sustains the livelihoods of more than 100 million people living along the coasts of Indonesia, Malaysia, Papua New Guinea, the Philippines, the Solomon Islands and Timor-Leste.
It’s also home to a lot of plastic.
Much of the waste clogging the waters of Coral Triangle countries is the result of poor waste management at the local and national levels. But a recent study published in the Journal of Marine Science and Engineering shows that plastic also comes from much farther afield. It found that microplastics in the Mekong River in mainland Southeast Asia are spreading to the densely populated coasts of the archipelagic countries of the Philippines and Indonesia.
As the region hosts some of the richest fauna and flora on the planet, experts say these findings show that cooperation between Southeast Asian nations is crucial to reduce the harm done to marine life and the communities that depend on aquatic resources.
Earth, wind and water
The Mekong River provides livelihoods to about 1.3 billion people, but is also one of the top contributors to plastic pollution in global oceans, making it a critical area for research to understand how to reduce marine plastic waste.
Using the OpenDrift software to model trajectory, the authors of the study simulated the release of plastic particles in the river and let them drift for 10 months.
The scientists also ran simulations for dry and flood conditions, modeling the release of plastics every day from June to August 2020, and again from December 2020 to February 2021.
They concluded that the drift was highly seasonal, due to the strong influence of monsoon systems in the South China Sea, which leads to a sharp increase in rainfall from June that peaks in late October or early November.
“In the dry season — from January to May, garbage accumulates in landfills,” Dung M. Nguyen, an oceanographer at the Norwegian Meteorological Institute and one of the authors of the paper, told Mongabay in an email. During the monsoon, garbage follows the flood to the sea, he added.
The researchers considered the impact of wind as well. In the rainy season, prevailing winds sent most plastics to the western coast of Malaysian Borneo and the Philippines; in the dry season, winds about twice as strong directed them toward Thailand and Peninsular Malaysia.
However, ocean currents were found to be far more significant in spreading particles than wind; wind drift acts only on the first few dozen centimeters of water, roughly a foot below the surface, while plastics dispersed to depths of up to 5 meters (16 ft).
Nguyen said the three-month simulations didn’t allow for enough time for garbage to reach the coasts of nearby countries. But after 15 months, the scientists found that around 96% of the plastic particles were stranded: the Philippines accumulated 47% of them, and Indonesia 24%.
Plenty of plastics in the sea
The study does have limitations. For instance, in reality, plastics are mostly released into the sea during the flood season, making the researchers’ dry-season scenario less realistic. In addition, the model assumed that if a plastic particle hit the coast, it would be stranded indefinitely, whereas in practice, some types of plastic may return to the sea.
But the authors say they hope their research can help authorities across Southeast Asia develop plans to better deal with plastic waste at sea.
“The focus on plastic pollution in the marine environment can be explained by the impacts it may have on the tourism sector and on the possible human health risks posed by contaminated sea food,” says another study published in Frontiers in Environmental Science in 2021.
Nguyen cited coastal amusement parks in the Mekong region had even lost visitors due to large amounts of garbage stranded along the coasts.
Several studies also show that in Indonesia, which is particularly exposed to the Mekong plastic drift, some commercial edible fish and bivalves are contaminated by microplastics. Other species present in Indonesian waters, like whale sharks and manta rays, are also highly susceptible to plastic pollution.
The scale of the problem prompted the Indonesian government last year to pay thousands of traditional fishers to collect plastic trash from the sea as part of the country’s efforts to cut marine plastic waste by 70% by 2025.
Plastic pollution is estimated to kill more than 100,000 marine mammals every year, through entanglement, starvation or drowning, according to data from the United Nations.
“Plastic waste will remain in the environment for a million years, thus negatively impacting wildlife as well the livelihoods of the people,” Rocky Pairunan, Indonesia plastic waste and ocean manager at the World Resources Institute (WRI), wrote in an email to Mongabay.
He expressed optimism, however, about Indonesia’s progress, noting that the government recently announced a 35% reduction in marine plastic pollution leakage between 2018 and 2022.
“The next step is … to issue a stricter legislation and take a firm enforcement to ensure that the local governments share the responsibilities and take the proper actions to reduce and manage household waste, by prioritizing public financing for improved waste collection and processing, together with behaviour change program,” he said.
Garbage without borders
Nguyen said he expected growing awareness of Mekong plastic drift to promote cooperation in the region.
“Because the impact of plastic leakage to the marine environment is transboundary, or goes beyond a particular national jurisdiction, we believe that efforts to avoid or mitigate the leakage must be collectively done,” Rocky said. The regional action plan against marine debris by the Association of Southeast Asian Nations (ASEAN), which facilitates exchange among members, for example, should start with more ambitious goals.
“ASEAN needs to step up to show its leadership and come up with concrete strategic actions to address plastic pollution,” Rocky said.
For Marilyn Mercado, WWF’s regional plastic policy coordinator for Asia, “the fact that plastic pollution does not respect national borders demonstrates why the U.N. plastic pollution treaty with common global binding rules is so desperately needed.”
“Establishing global control measures with complementary national actions is the only way to fully address the transboundary nature of plastic pollution, the global nature of the plastic value chain, and to level the playing field for governments and industry,” she wrote in an email to Mongabay.
U.N. member states, who met in Paris in May to discuss the development of what would be the first global treaty to combat plastic pollution, have agreed to present a draft by November this year. WWF welcomed this in a recent statement as “tangible progress.”
The conservation organization is calling on governments to take measures across the whole plastic life cycle, and in particular to support global bans and phase-outs of the most high-risk and unnecessary single-use plastic products, such as plastic cutlery or e-cigarettes, Mercado said.
According to the United Nations Environment Programme (UNEP), mismanaged plastic waste ending up in the environment could decline by 80% by 2040 if the world adopts deep policy and market changes.
Banner image: Plastics in the Mekong River drift to the coasts of Southeast Asian countries. Image by Nataliya Vaitkevich via Pexels (Public domain).
Nguyen, D. M., Hole, L. R., Breivik, Ø., Nguyen, T. B., & Pham, N. Kh. (2023). Marine plastic drift from the Mekong River to Southeast Asia. Journal of Marine Science and Engineering, 11(5), 925. doi:10.3390/jmse11050925
Vriend, P., Hidayat, H., Van Leeuwen, J., Cordova, M. R., Purba, N. P., Löhr, A. J., … Van Emmerik, T. (2021). Plastic pollution research in Indonesia: State of science and future research directions to reduce impacts. Frontiers in Environmental Science, 9. doi:10.3389/fenvs.2021.692907
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