Oceans now hold 250,000 tons of plastic trash
And that does not include the plastic that has washed up on beaches or sunk to the sea bed.
The scientists from the 5 Gyres Institute came up with the figure after trawling nets during 24 expeditions between 2007 and 2013 across all five sub-tropical ocean gyres, coastal Australia, Bay of Bengal and the Mediterranean Sea.
Their research was published in PLOS One.
The discovery of the impact of discarded plastic is relatively recent. The Great Pacific Garbage Patch – about the size of Texas – was discovered when Charles Moore stumbled across it while returning from the Transpacific Yacht Race in 1997.
Moore returned earlier this year to discover that the plastic had coalesced into islands with their own ecosystems.
The latest estimates of the scale of the problem show that it has worsened rapidly in the past three decades. In the 1970s, studies suggested that about 45,000 tons of plastic littered the ocean.
There is now virtually no ocean that is free of the scourge but undoubtedly the North Pacific is the worst affected with more than a third of the total plastic found in the oceans, according to the latest study.
Moore, one of the paper's coauthors and founder of marine research and lobby group Algalita, said the estimate was conservative.