Oceanic plastic disappearance via rivers: Vanished with the currents

A groundbreaking study, published in the prestigious journal Science, has challenged the long-held belief that developing countries with poor waste management systems are the primary sources of microplastic pollution in the oceans. The research, conducted by the Leibniz Centre for Tropical Marine Research, the Australian scientific agency CSIRO, and the University of Toronto, has shed new light on the issue and highlighted the urgent need for global cooperation to combat microplastic pollution.

The study identifies several methodological errors that led to inaccurate assessments of the fluxes and overall mass of microplastics discharged by rivers into the sea at a global scale. The main methodological mistakes included 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).

As a result, the global river flux estimates for microplastics discharged into the sea are now believed to be two to three orders of magnitude less than previously thought. This revelation has significant implications for our understanding of microplastic pollution in marine environments, as it suggests that the floating stock of microplastics on the ocean’s surface is a small fraction of the plastic discharged by rivers.

One of the most striking findings of the study is that microplastic pollution in marine environments originates from countries with well-established waste management systems, not just developing countries with little waste management. This discovery challenges the common perception that the problem is primarily a result of poor waste management practices in certain regions.

The study also estimates that rivers deliver several million metric tons of plastic annually to the oceans. If the discharge of microplastics from rivers to the sea were to stop today, the amount of floating particles and their harmful effects on marine ecosystems would persist for at least several more years, due to the average residence time for microplastics at the surface of the oceans being a few years, as opposed to only several days as previously estimated.

The search for the missing 'plastic sink' in the ocean has been concluded, as the missing plastics have been found through the correction of the river flux estimate. This discovery underscores the importance of global cooperation and action to combat microplastic pollution in the marine environment.

The field of scientific research on the impacts of plastics on the marine environment is still in its early stages, and much research is needed to understand how plastics cycle in the oceans, including plastic size classes, oceanic compartments, and land-to-sea transfer processes. The study also highlights the urgent need for further research to properly evaluate the stock sizes and exchange fluxes between compartments in the ocean related to plastics.

Dr. Wolfgang Ludwig, the Director of the CEFREM laboratory and co-author of the study, emphasizes the need for global action to change consumption habits, better manage waste, and target sources of microplastic waste generation to combat microplastic pollution. The DOI for the study published in Science is 10.1126/science.abe0290. The study's findings contribute to the ongoing fight to preserve our planet's oceans and seas from the harmful effects of microplastic pollution.