This in from the Smithsonian:
Plastic is the most pervasive pollutant in the ocean today. But researchers have struggled to estimate just how much of the 6 billion tons of plastic that has been manufactured since the mid-20th century ultimately winds up in the ocean.
Based on the calculations, at least 5.25 trillion pieces of plastic—weighing nearly 269,000 tons—are currently bobbing around in the ocean. A team of researchers from six countries reported the finding today in PLOS ONE.