Environment: where does ocean plastic come from?

Bottles, tires, packaging or pipes… Several million tons of plastic waste are dumped each year into waterways and can end up in the oceans. Their quantity could double by 2060 without increased action against this pollution, according to the OECD.

From the mass production of this material in the 1950s to 2019, 140 million tons of plastic have already accumulated in aquatic environments, according to a 2023 study by the Organization for Economic Co-operation and Development (OECD), of which 22% forms a “plastic soup” in the oceans and 78% in freshwater ecosystems.

Waste burned in the open air or dumped in uncontrolled or illegal landfills is the main source of pollution in aquatic environments. A large proportion of these plastics, such as bottles or plastic used in construction, flows into rivers and lakes. The rest will float (food packaging, closed bottles) for “years or even decades” and end up in the oceans, explains the OECD.

Marine waste (nets, fishing gear) is, to a much lesser extent, another source of plastic waste in the oceans, as are microplastics (pieces of plastic smaller than 5 millimetres). With an average lifespan of six months to 35 years, accumulated macroplastics (larger than 5 mm) slowly decompose into microplastics, “more likely to be ingested by aquatic species”, adds the OECD.

But the risk of plastic migrating from land to waterways, then from rivers to sea, is not the same everywhere. Out of some 100,000 waterways, a thousand are responsible for 80% of macroplastic waste in the oceans and 30,000 represent the remaining 20%, calculated several researchers in a study led by the NGO Ocean Cleanup and published in 2021 in the journal Science Advances. Of the top 50 rivers carrying plastic to the oceans, including small urban waterways, 44 are located in Asia, due to “population density and poor waste management,” Laurent Lebreton, research director at Ocean Cleanup, told AFP. The Philippines, with its thousands of islands, is the country that dumps the most plastic into the sea.

Flowing into Manila Bay, the Pasig River is the “most polluted” by plastic in the world. Along with the Tullahan (Philippines), Ulhas (India), Klang (Malaysia) and Meycauayan (Philippines) rivers, it forms the top 5 rivers carrying the most plastic into the oceans. Driven by population and economic growth, global plastic use is expected to almost triple between 2019 and 2060, to 1,231 million tonnes (Mt) per year, according to the OECD. Gloomy forecasts for aquatic environments where 493 Mt of plastic could be accumulated by 2060, more than half of which will come from sub-Saharan Africa, China, India and other developing Asian countries, the organization predicts.

In Europe and the United States, on the other hand, plastic discharges into aquatic environments should decrease, in particular “thanks to improved waste management.”

Sami Nemli With Agency / Les Inspirations ÉCO