FRESH MULLET: January 2013

Plastic bottles and other garbage block a dam in Bulgaria. Such debris can make its way into oceans.

Australian scientists say it will take at least 500 years to stop the growth of five swirling masses of plastic waste in the world's oceans.

Even that grim scenario would depend on an immediate ban on more plastic going into oceans, they say.

A swirling mass of plastic debris was first discovered in the so-called north Pacific gyre about 15 years ago.

Since then more areas of plastic have been discovered in other oceans.

They have created soup-like areas of manmade material.

A team of researchers at the Australian Research Council centre of excellence for climate system science has been investigating how they form.

Dr Erik Van Sebelle leads researchers at the centre.

He told Radio Australia's Pacific Beat the research shows the plastic accumulation is an extremely slow process. But it has seriously long-term impacts.

"Even if we were to stop getting any plastic into the ocean tomorrow . . . then these patches would continue to grow for at least another 500 years," he said.

"They would just grow and grow and grow because of all the plastic we put in the ocean already that hasn't even accumulated in these patches yet."