The world's leading expert on the poisoning of the oceans has described how he was "utterly shocked" by the true amount of plastic floating on the sea, warning that it potentially posed a bigger threat to the planet than climate change.
Charles J Moore, a captain in the US Merchant Marine fleet and founder of a leading ocean research group, has just finished his first in-depth survey of the Great Pacific Garbage Patch - one of five major expanses of plastic drifting in the world's oceans - since 2009, and said he was staggered by the increase.
"It's choking our future in ways that most of us are barely aware," said Captain Moore.
He first caught sight of the huge patch of rubbish in the North Pacific Ocean, which has been compared to a floating landfill site, while returning to southern California after the Los Angeles-to-Hawaii Transpacific yacht race in 1997.
He has since revisited the area with a team of scientists 10 times, and found an alarming rise in the amount of refuse in the past five years.
"Plastics of every description, from toothbrushes to tyres, to unidentifiable fragments too numerous to count, floating for hundreds of miles without end," Captain Moore wrote in a column in The New York Times.
"We even came upon a floating island, bolstered by dozens of plastic buoys used in oyster aquaculture, which had solid areas you could walk on."
Plastics are now one of the most common pollutants of ocean waters. Pushed by winds, tides and currents, particles collect with other debris to form large, swirling, glue-like accumulation zones.
These are known to oceanographers as "gyres", which comprise as much as 40 per cent of the planet's ocean surface, said Captain Moore, who founded the Algalita Marine Research Institute in Long Beach, California.
In a previous study of southern California's urban centres, he calculated that they spilled 2.3 billion pieces of plastic - from polystyrene foam to tiny fragments and pellets - into the area's coastal waters in just three days of monitoring.
Once in the sea, the plastics biodegrade extremely slowly, breaking into minute pieces in a centuries-long process. They entangle and slowly kill millions of sea creatures, and hundreds of species mistake them for food, ingesting toxicants that cause liver and stomach problems in fish and birds, and often choke them.
"We suspect that more animals are killed by vagrant plastic waste than by even climate change - a hypothesis that needs to be seriously tested," Captain Moore said.
The problem is exacerbated by the fishing industry, which uses plastics in floats, lines and nets, which are often lost through accidents.
Although a handful of methods exist to reduce the volume of plastic at sea, their effects pale into insignificance against the scale of the heaps.
"The reality is that only by preventing man-made debris from getting into the ocean in the first place will a measurable reduction be accomplished.
"The real challenge is to combat an economic model that thrives on wasteful products and leaves the problem of clean-up costs. Changing the way we produce and consume plastics is a challenge greater than reining in our production of carbon dioxide."
- UK Independent