by Frank Pope

A high-seas mission departs from San Francisco next month to map and explore a sinister and shifting 21st-century continent: one twice the size of Texas and created from six million tonnes of discarded plastic.

Scientists and conservationists on the expedition will begin attempts to retrieve and recycle a monument to throwaway living in the middle of the North Pacific.

The toxic soup of refuse was discovered in 1997 when Charles Moore, an oceanographer, decided to travel through the centre of the North Pacific gyre (a vortex or circular ocean current). Navigators usually avoid oceanic gyres because persistent high-pressure systems — also known as the doldrums — lack the winds and currents to benefit sailors.

Mr Moore found bottle caps, plastic bags and polystyrene floating with tiny plastic chips. Worn down by sunlight and waves, discarded plastic disintegrates into smaller pieces. Suspended under the surface, these tiny fragments are invisible to ships and satellites trying to map the plastic continent, but in subsequent trawls Mr Moore discovered that the chips outnumbered plankton by six to one.

The damage caused by these tiny fragments is more insidious than strangulation, entrapment and choking by larger plastic refuse. The fragments act as sponges for heavy metals and pollutants until mistaken for food by small fish. The toxins then become more concentrated as they move up the food chain through larger fish, birds and marine mammals.

“You can buy certified organic farm produce, but no fishmonger on earth can sell you a certified organic wild-caught fish. This is our legacy,” said Mr Moore.

Because of their tiny size and the scale of the problem, he believes that nothing can be solved at sea. “Trying to clean up the Pacific gyre would bankrupt any country and kill wildlife in the nets as it went.”

In June the 151ft brigantine Kaisei (Japanese for Planet Ocean) will unfurl its sails in San Francisco to try to prove Mr Moore wrong. Project Kaisei’s flagship will be joined by a decommissioned fishing trawler armed with specialised nets.

“The trick is collecting the plastic while minimising the catch of sea life. We can’t catch the tiny pieces. But the net benefit of getting the rest out is very likely to be better than leaving it in,” says Doug Woodring, the leader of the project.

With a crew of 30, the expedition, supported by the Scripps Institution of Oceanography and Brita, the water company, will use unmanned aircraft and robotic surface explorers to map the extent and depth of the plastic continent while collecting 40 tonnes of the refuse for trial recycling.

“We have a few technologies that can turn thin plastics into diesel fuel. Other technologies are much more hardcore, to deal with the hard plastics,” says Mr Woodring, who hopes to run his vessels on the recycled fuel.

Plastics bags, food wrappers and containers are the second and third most common items in marine debris around the world, according to the Ocean Conservancy, which is based in Washington. The proportion of tiny fragments, known as mermaid’s tears, are less easily quantified.

The UN’s environmental programme estimates that 18,000 pieces of plastic have ended up in every square kilometre of the sea, totalling more than 100 million tonnes. The North Pacific gyre — officially called the northern subtropical convergence zone — is thought to contain the biggest concentration. Ideal conditions for shifting slicks of plastic also exist in the South Pacific, the Indian Ocean and the North and South Atlantic, but no research vessel has investigated those areas. If this exploratory mission is successful, a bigger fleet will depart in 2010.

Mr Woodring admits that Project Kaisei has limitations. “We won’t be able to clean up the entire ocean. The solution really lies on land. We have to treat plastics in a totally different way, and stop them ever reaching the ocean.”