There are an estimated 5.25 trillion pieces of plastic floating in the world's oceans, weighing a total of nearly 270,000 tons, according to a new study.

Plastic has “spread throughout all the world's oceans" with as much in the southern hemisphere as the northern, the researchers said, adding that this was surprising as more of it originates in the north.

In an article for the Pios One journal, they

said the figures were "highly conservative" and did not take into account "the potentially massive amount" that is no longer afloat.

Julia Reisser, a researcher with the University of Western Australia, told The Guardian: "We saw turtles that ate plastic bags and fish that ingested fishing lines.

"But there are also chemical impacts. When plastic gets into the water it acts like a magnet for oily pollutants.

"Bigger fish eat the little fish and then they end up on our plates. It's hard to tell how much pollution is being ingested but certainly plastics are providing some of it."

The article cited trade body Plastics Europe as saying 288 million tons of plastic were produced world-wide in 2012.

"Our estimate of the global weight of plastic pollution on the sea surface, from all size classes combined, is only 0.1 per cent of the world annual production," it said.