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Mysterious ocean plastic sink is no longer missing

The mystery of missing ocean plastic comes down to a simple case of human error, according to a new study from the University of Barcelona. The researchers found that estimates of river flux are overestimated by two to three orders of magnitude, which explains why a large volume of microplastics has been unaccounted for.

Unfortunately, the study does not indicate that ocean plastic is any less of an issue. On the contrary, the researchers found that plastics persist at the ocean’s surface much longer than expected, allowing them to cause even more damage. 

Rivers are the leading source of marine plastic pollution – estimated to deliver several million metric tons of plastic to the ocean each year. However, the actual quantity of plastics found floating on the ocean’s surface has been tens to hundreds of times lower than what was thought to be dumped through rivers. This major discrepancy led to the theory that there is a missing ocean plastic sink.

“We can now confirm that the search for the missing ‘plastic sink’ is over, as the missing plastics have been found through the correction of the river flux estimate,” said study co-author Professor Miquel Canals, head of the Consolidated Research Group on Marine Geosciences at the University of Barcelona.

The researchers identified the main methodological mistakes which led to inaccurate assessments of the overall mass of ocean plastic discharged by rivers. 

“The in situ data that we now have for microplastics in rivers, compared to early empirical modeling studies, allowed us to assemble a robust database which we were then able to analyze to obtain a more reliable estimate for the quantity of microplastics being discharged from rivers into the sea,” explained study lead author Dr. Lisa Weiss from the CEFREM laboratory at the University of Perpignan.

“This process revealed several significant methodological errors in previous flux estimates. When we then corrected these mistakes we found that the global river flux estimates are two to three orders of magnitude less than previously thought.” 

“Further, we found that the average residence time for microplastics at the surface of the oceans may actually be a few years as opposed to only several days, as previously estimated.”

According to study co-author Dr. Wolfgang Ludwig, the Director of the CEFREM laboratory, the only way we are going to have a chance at winning the fight against microplastic pollution will be to target the sources where microplastic waste is generated. 

“We need to take action at the human level. We need to change our consumption habits, better manage our waste and we need to do this at a global scale,” said Dr. Ludwig.

“Our study shows that marine microplastic pollution not only comes from developing countries – with little to no waste management – as one might think, but also comes from countries with well-established waste management systems.”

“If we were to stop the discharge of microplastics from rivers to the sea today, the amount of floating particles and their harmful effects on marine ecosystems would persist for at least another several years.”

The study is published in the journal Science.

By Chrissy Sexton, Staff Writer

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