1% of rivers globally found responsible for most plastic emissions into the ocean

Sampriti Roy, University of Calcutta

British philosopher Timothy Morton defines a hyperobject as something that is so widely distributed in space and time such that it surpasses spatiotemporal specificity. This concept applies to Global Warming, radioactive plutonium and something that is a constituent of at least one item in front of you right now- microplastic. Microplastic is something that we consume every day in little amounts and is a problem that is being researched all over the world right now. The only long term solution to it is tracking down its source, i.e. macroplastic, and applying mitigation policies. This is why the recent study done by The Ocean Cleanup (whose primary area of focus is Ocean plastic pollution) could be considered an important breakthrough. 

Published in Science Advances, the study points out the various sources of mismanaged plastic waste that reach oceans from around the world and notes the importance of rivers in the same as well as in causing inland aquatic pollution. Out of the 100,000 rivers and creeks that exist worldwide, only an estimated 1000 (i.e. 1%) small and medium-sized rivers have been found to carry about 80% of the global riverine plastic emissions into the oceans. More alarming is the fact that Asia consists of the top 5 countries (India, Malaysia, China, Indonesia and Philippines) emitting the most riverine plastic, with the countries accounting for 79.7% of all emissions. 

Addressing the need to generate a more holistic model

Earlier studies (before 2017) suggested that about 5-47 rivers generated about 80% of riverine plastic emissions. However, it was observed from data gathered from 2017 onwards that the problem spanned a lot more rivers than previously thought. Study features include:

• Parametrization: With the help of Earth scientists, field campaign insights, plastic experts and data from about 136 field measurements that represented “67 rivers in 14 countries of 3 continents” collected between 2017 and 2020, their probabilistic model was parameterized.

• Some of the important parameters taken into account: 

i) Rain and wind were listed as additional driving forces to the parameters present in the existing literature. These parameters are said to have contributed to the study being more robust since it will help distinguish between river basins with varied environments.

ii) Land use and Terrain slope: Terrain characteristics play a big role in determining the nature of the journey of plastic. This was included to differentiate how plastic moves over various landscapes.

iii) River characteristics: Size along with the downstream trajectory of the river was considered since larger rivers will be able to carry and transport more plastic than smaller and shallower rivers.

iv) Mismanagement: The locations of a plastic generation that were being mismanaged were incorporated about the river nearest to them along with the distance that plastic waste would be required to travel downstream from the entry point into the river to the river mouth at the ocean.

• Holistic data generation to account for riverine plastic transport: 

i) It was obtained by using global data sets. The data utilized were obtained in the following domains: terrain slope, flow direction (HydroSHEDS), land use data (GLC2000), runoff data (GRUN), precipitation and wind data (WorldClim2), and elevation (DEM).

ii) By using this data, a global river network was calculated, along with river classes, the distance from every location on Earth towards the river or ocean that was nearest to it and the transport and mobilization probabilities of the plastic waste emissions.

iii) The probability for mismanaged plastic waste to reach the ocean for each grid cell was then figured out.

iv) The corresponding badly managed plastic waste and its accumulation within a river basin was then multiplied by the plastic emission probability. The results represented annual plastic emissions per river mouth.

Some countries must worry more about plastic emissions

“Cumulative mismanaged plastic waste production” and “average probability of plastic reaching the ocean” are the key factors in addressing a country’s plastic emissions. Plastic waste generation by any country also depends upon the management of plastic waste. Some countries have a high plastic consumption along with a good waste management system. So, the trash produced by them is lower than expected and thus, lesser plastic reaches the ocean from them. 

Aside from mismanagement, there are a few other factors as well that account for a country’s riverine plastic waste emissions. We see that China’s mismanaged plastic waste production is of a higher order of magnitude than the Philippines, but it is the Philippines that emits more plastic into the ocean. Aside from management, this is due to:

i) Geography: Distance to the nearest river/ ocean (China is a land-locked country while the Philippines is a coastal one).

ii) Climate of the archipelago (as compared to China) in terms of rainfall rates.

iii) Difference in population densities 

So, countries with extensive riverine networks, high population density and coastal habitation (like India) must have more robust measures for reducing plastic waste emissions than land-locked countries.

The need for a Global Action Plan

We now know about the 1000 most polluting rivers. We know that applying mitigation measures to them is feasible. We know also that most of the polluting rivers aren’t as massive as the Amazon but are relatively small/ medium-sized.

What now?

It is now up to governments to apply tailored mitigation measures since there cannot be a one-size-fits-all solution to the problem of mismanaged plastic reaching the ocean through rivers (as seen by the example of China and the Philippines). Land-based solutions are more important than ever because according to the findings of The Ocean Cleanup, it is only 1.5% of the mismanaged plastic waste that reaches the ocean. The other 98.5% goes on to accumulate and pollute inland aquatic ecosystems.

By identifying the problem, rectifying previous estimates and providing renewed parameters for a more accurate estimation of the main sources of plastic into the ocean, The Ocean Cleanup has provided a study that will help concerned bodies to identify the main areas lacking proper management policies. The Data is right there. The evidence of progressive deterioration in the management of plastic waste of countries is right there. What must be done now is designing solutions to target plastic at the source and implementing it.

Also read: Tata Memorial Hospital Clinical Research Associate For Life Sciences

Reference:

• Meijer, L. J., van Emmerik, T., van der Ent, R., Schmidt, C., &Lebreton, L. (2021). More than 1000 rivers account for 80% of global riverine plastic emissions into the ocean. Science Advances, 7(18), eaaz5803.
• https://theoceancleanup.com/updates/in-search-of-the-rivers-that-carry-plastic-into-the-ocean/

• The Corrosion Prediction from the Corrosion Product Performance
• Nitrogen Resilience in Waterlogged Soybean plants
• Cell Senescence in Type II Diabetes: Therapeutic Potential
• Transgene-Free Canker-Resistant Citrus sinensis with Cas12/RNP
• AI Literacy in Early Childhood Education: Challenges and Opportunities