Rivers carry away ocean plastic, leaving it vanished in landfills and water bodies.

In a groundbreaking study published in the prestigious journal Science, researchers have shed light on the origins of microplastic pollution in our oceans. The study, led by Dr. Lisa Weiss and Dr. Wolfgang Ludwig, highlights the significance of rivers as the primary source of plastic discharge.

The research, which also includes Professor Miquel Canals of the University of Barcelona, uncovers that microplastic pollution does not solely stem from developing countries, but also from countries with well-established waste management systems. The majority of microplastic pollution entering the oceans from rivers originates mainly from China, India, South Asia, Africa including the Middle East. About 90% of plastic emissions come from ten rivers, eight in Asia (including the Yangtze, Indus, Yellow River, Hai He, Ganges, Pearl River, Amur, and Mekong) and two in Africa (the Nile and Niger).

The study underscores that our understanding of how plastics cycle in the oceans is still emerging, and there is much more to learn about the impacts of plastics on marine ecosystems. It stresses the importance of targeting sources where microplastic waste is generated and changing consumption habits, waste management, and these actions need to be taken at a global scale.

One of the key findings of the study is the correction of the river flux estimate, which has led to the discovery of the so-called 'plastic sink'. Contrary to previous assumptions, the floating stock of microplastics on the ocean’s surface is just a small fraction of the plastic discharged by rivers. The average residence time for microplastics at the surface of the oceans may actually be a few years, as opposed to only several days.

The study also identifies the main methodological mistakes that led to inaccurate assessments of the fluxes and overall mass of microplastics discharged by rivers into the sea at a global scale. These mistakes include a systematic overestimation of the average microplastic particle weight in river samples, the integration of incompatible data, and assessments based on the relation between microplastic fluxes and the MPW index (mismanaged plastic waste).

The new study emphasizes the need for further research on plastic size classes, oceanic compartments, and land-to-sea transfer processes to properly evaluate the stock sizes and exchange fluxes between compartments. The scientific community must work together to overcome inertia from the past, correct mistakes, and use common protocols and guidelines to provide the best decision-making advice for protecting oceans and seas.

The study, with the DOI 10.1126/science.abe0290, was conducted by a team including Dr. Lisa Weiss from the Centre of Education and Research on Mediterranean Environments (CEFREM), University of Perpignan, and Dr. Wolfgang Ludwig, the Director of the CEFREM laboratory. The research was also supported by a team of researchers from various research institutions in France and the University of Barcelona in Spain.

The study serves as a call to action, stressing that we have only just begun to understand the magnitude and complexity of microplastic pollution in our oceans and seas, and more research is necessary to combat this global issue effectively.