Welcome to the world’s largest garbage dump(2)

Plastic soup

However, rather than floating trash islands, marine garbage patches are not wholly visible. Instead, the glassy calm waters are saturated with microscopic particles of degrading inorganic material that form a "plastic soup".

Like giant conveyor belts, the ocean currents can carry material vast distances. During a storm in January 1992, a ship spilled a container carrying 29,000 made-in-China plastic toy ducks into the Pacific Ocean.

Fifteen years later, a retired teacher found one of the yellow ducks as she walked her dog on a beach in Devon, southwest England. In the wake of the first toy, which had floated an estimated 17,000 miles, a further 10,000 arrived on Britain's beaches, while others headed to other destinations, including the Arctic, the US and Indonesia.

While it's estimated that as many as 10,000 containers fall off ships every year, causing shipping hazards and threatening marine life, they are not the largest sources of ocean debris.

"(Marine debris is) mostly land-based. Some comes from ships or fishing vessels, and some from catastrophic events, such as tsunamis, hurricanes and cyclones," said Eriksen.

"All garbage patches contain massive amounts of micro-plastics from unidentifiable origins. We can only identify micro-plastic pellets, which are oval-shaped. The large plastic items are usually fishing gear, such as buoys and lost nets. We also find plenty of bottle caps, bottles, bags, buckets, crates and other miscellaneous throwaway plastics," he wrote.

In a 2006 report called Plastic Debris in the World's Oceans, Greenpeace estimated that around 80 percent of marine trash comes from land-based sources, such as tourism- and sewage-related debris on coasts and the rest comes from ocean-based sources, such as fishing nets and lines and waste from ships and boats.

Garbage from all over the world spends one to six years reaching the Great Pacific Garbage Patch. During the voyage, the process of photo-degradation splits the plastic into smaller and smaller pieces, which float with the currents and are distributed globally.

According to the UN, of the 300 million metric tons of plastic produced globally every year, about 6 million tons end up in the oceans. Eighty percent of the waste is either washed into the sea by rivers or is carried on the wind from garbage dumps.

A long-term problem

The longevity of plastics mean the problem will be around for a long time yet. The US Environmental Protection Agency has calculated that microfilament fishing line takes 600 years to fully degrade, while plastic bottles take 450 years, and styrofoam buoys can last as long as 80 years.

In 2008, researchers from the 5 Gyres Institute trawled the Pacific patch using superfine nets, which snared plastic and plankton alike, and then weighed the results. They concluded that the density of plastic in the Pacific patch had risen to a ratio of 46-to-1 plastic to plankton by weight from 6-to-1 in 1999.

In 2010, scientists from the US-based Sea Education Association told the Ocean Sciences Meeting in Portland, Oregon, that the density of plastic debris in the Atlantic Ocean north of the Caribbean had reached 200,000 pieces per square kilometer, but that it was impossible to measure the exact size of the patch because much of the debris was floating beneath the surface.

According to the SEA, the density was such that it was comparable with the Great Pacific Garbage Patch. The association noted that the "North Atlantic Garbage Patch" has the highest concentration of plastic, most of it originating in the US, Canada, Mexico and Europe.

This plastic ocean soup poses a severe threat to marine life, and ultimately, humans. Oceanographers have discovered micro-plastics inside zooplankton, which, if consumed by fish and other creatures higher up the food chain, could eventually find their way into human stomachs. In addition, many of the micro-plastics contain poisonous materials, such as Bisphenol A, which can be released into seawater by photo-degradation.

Plastics derived from Bisphenol A have become hugely popular since they were developed in the 1950s. Their high resistance to heat and shattering, plus the great visual clarity they provide, mean they are perfect for the manufacture of items such as CDs, computers, sports equipment and food and drink containers, among other things.