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How does plastic arrive into our oceans?

A Nature Communication’ study reveals plastic input temporal variations and the most threatening rivers to our oceans.

Plastics are increasingly used all over the world in a wide variety of applications with global production more than 300 million tonnes per year since 2014. Because of their durability, low-recycling rates, poor waste management and maritime use, a significant portion of the plastics produced worldwide ends up and persists in shoreline, seabed, water column and sea surface environments of the world’s oceans. Plastics arrive into the marine environment through different ways, including river and atmospheric transport, beach littering and directly at sea via aquaculture, shipping and fishing activities. Implementing strategies to reduce our plastic inputs into the oceans requires an understanding and quantification of marine plastic sources, taking into account spatial and temporal variability.

A Nature Communication’s study estimates that every year between 1.15 and 2.41 million tonnes of plastic currently flows from the global riverine systems into the oceans. The top 122 polluting rivers contribute for more than 90% of the plastic inputs with 103 rivers located in Asia, eight in Africa, eight in South and Central America, and one in Europe. The top 20 polluting rivers account for more than two thirds (67%) of the global annual input and are mostly located in Asia. Considerably high-population density combined with relatively large mismanaged plastic waste production rates and episodes of heavy rainfalls lead to an estimated annual input of 1.21 million tonnes per year from Asian continent, which means 86% of the total global input.

According to Nature Communication’s model, the Chinese Yangtze River is the largest contributing catchment, with an annual input of 0.33 million tonnes of plastic discharged into the East China Sea. It is followed by the Ganges River catchment, between India and Bangladesh, with a computed input of 0.12 million tonnes per year. The combined input of the Xi, Dong and Zhujiang Rivers in China all flowing into the South China Sea at the Pearl River delta, is estimated at 0.106 million tonnes per year, placing the greater catchment into third position.

The rest of the world shares the remaining 14% of river plastic mass input, with 7.8% coming from Africa, 4.8% from South America, 0.95% from Central and North America, 0.28% from Europe, and the remaining 0.02% from the Australia-Pacific region.

The study reveals also a seasonal variations in river plastic inputs into oceans worldwide. It estimates that 74.5% of the total river plastic input occurs between May and October, with a peak in global inputs for the month of August. The month with the lower plastic input rate is January. These seasonal findings were mainly driven by the large inputs from China which are regulated by the East Asian monsoon and rainfall’s rate changes.

Plastics in the marine environment have become a major concern because of their persistence at sea, and adverse consequences to marine life and potentially human health. The Ocean Cleanup is a Dutch non-profit foundation which aims to eliminate plastics from our oceans thorough the Interceptor: a floating “coastline” that can collect plastics and debris spread across millions of square kilometres (if you have not read our article about it, you can find it here

In May 2020 Benioff Ocean Initiative has awarded The Ocean Cleanup $1 million to deploy an Interceptor in Kingston Harbour (Jamaica) in a multi-year project. Hunts Bay, which pours into Kingston Harbour, is Jamaica’s highest polluted waterway, responsible for an estimated 578,000 kg of plastic flowing into the ocean each year, which is roughly the weight of 80 African elephants. The company will install the Interceptor in collaboration with Recycling Partners Jamaica, who will help to drive the behavioural changes needed to sustain the efforts and will also manage the Interceptor, ensuring the proper disposal of all collected plastics and materials.

The Jamaica project will follow the implementation of Interceptors in Jakarta (Indonesia), Klang (Malaysia), and in Santo Domingo (Dominican Republic). Th foundation is also planning to install its system in Vietnam, Thailand, and Los Angeles County.



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