video: Plastics are a growing problem for natural ecosystems around the globe, and in particular for our marine and freshwater environments. Rivers are the leading source of plastic pollution, as it has been estimated that they deliver several million metric tons of plastic annually to our oceans from poor land-based waste management. The problem is that the estimates made for plastics flowing from the rivers are tens to hundreds of times higher than the quantity of plastics floating on the ocean's surface. So where is all of this river-derived plastic actually going - is there a missing plastic 'sink' somewhere in the ocean? Are the estimates correct?
In a paper published today in Science, Dr. Lisa Weiss and her colleagues from the Centre of Education and Research on Mediterranean Environments (CEFREM), a joint research laboratory between the University of Perpignan (UPVD) and the French National Centre for Scientific Research (CNRS), and a team of researchers from a number of research institutions in France and the University of Barcelona in Spain demonstrate that current river flux assessments are overestimated by two to three orders of magnitude from previous estimates. This would explain why a large volume of microplastics seems to disappear into a mysterious ocean 'plastic sink'.
However, these findings do not suggest that plastics are less of a problem than previously thought. In fact, through their analyses, researchers actually found that plastics remain at the ocean's surface much longer than previously estimated - further exacerbating the effects of plastic pollution on natural systems.
Rivers are the main source of plastic discharge into the oceans. According to current assessments, the floating stock of microplastics on the ocean's surface - from tens to hundreds of metric tons - is just a small fraction of the millions of metric tons that are discharged by rivers each year. This unequal balance has led to the 'plastic sink' hypothesis whereby the amount of microplastics in the 'plastic sink' plus the plastics at the surface would equal those presumably discharged by rivers into the sea.
Credit: Centre of Education and Research on Mediterranean Environments (CEFREM)/ University of Perpignan (UPVD)/ French National Centre for Scientific Research (CNRS)