More and more plastic is floating in our oceans and seas. It comes from rubbish that we throw away on the street, fishnets that are discarded, and from washing synthetic clothing and brushing our teeth. All these different types of plastic together form the plastic soup in the seas and oceans.

Weathering, sunlight and wave action break down large pieces of plastic into small pieces. This causes serious pollution. In 1997, Captain Charles Moore sailed from Hawaii to southern California, taking an unusual route that took him through the North Pacific Gyre. There, in the middle of the Pacific Ocean, he saw pieces of plastic floating by every day. He later returned to the area to carry out research. There seemed to be a significantly higher concentration of plastic there than elsewhere in the ocean. The plastic appeared not only to float, but also to be carried by the water column. Moore called this phenomenon the ‘plastic soup’, a term which is now used around the world.

The oceans constitute 72% of the earth’s surface and are our primary oxygen suppliers. They are the primary source of food for more than half the world’s population. But because plastic is not biodegradable, the plastic soup is lethal for many marine animals.

plastic soup is becoming toxic and is entering our food chain

When plastic degrades and fragments into small pieces, it can release toxic substances. All sorts of animals that live in or from the sea, even minute zooplankton, mistake plastic and microplastics for food. These toxic substances then enter our food chain. On top of this, en route to the sea, plastic fragments absorb all kinds of toxic substances from the sewers and polluted areas that they pass through. They become toxic bombs. These substances are released in the bodies of the organisms that eat the plastic.

The plastic pollution of the seawater can also seriously damage our health. Most of the pollution by far comes from land. At least 80% of the plastic rubbish in the oceans are dumped by industry and by people on land. It is carried to sea by rivers, canals, harbours and the wind. On top of this, shipping, fisheries and the off-shore industry are important contributors to pollution, though compared to the land sources, this is ‘only’ 20%.

Part of the plastic that we use ends up in the oceans. What happens to it and where does it go? Plastic can be found on every beach in the world. Microplastics are found at 5,000 metres depth, and plastic bottles have been found at depths of 3,500 metres. It’s actually ‘raining’ plastic  in the ocean. Scientists are still far from mapping all the plastic pollution in the oceans.

Gyres

The rotation of the earth causes the oceans to continuously move and the winds to blow. There are five large rotating ocean currents that are called ‘gyres’. These are huge vortexes in which all floating objects are slowly sucked into the middle. It is comparable to the kitchen sink drain.

There are five major gyres on earth: the North Pacific, South Pacific, Indian Ocean, North Atlantic and the South Atlantic Gyre. They are in sub-tropical areas, above and below the equator. All five gyres have higher concentrations of plastic rubbish compared to other parts of the oceans. In the North Atlantic Gyre, 20,328 pieces of plastic were found per square kilometre, while in the North Pacific Gyre, this can be as high as 334,271 pieces per square kilometre. These pieces are largely made up of tiny fragments of less than 5 mm that we can barely see with the naked eye. These are the microplastics.

In the centre of the gyres there is no wind. These areas have traditionally been avoided by shipping. But in 1997 captain Charles Moore sailed from Hawaii to Southern California through the North Pacific Gyre. There, in the middle of the ocean, he saw pieces of plastic floating by every day. Later he returned to the area to do closer research. There appeared to be a significantly higher concentration of plastic then elsewhere in the ocean. The plastic appeared to not only float, but also to hang suspended below the surface. Moore called the phenomena plastic soup, the term now used worldwide.

The size of the North Pacific Gyre is said to be 34 times that of the Netherlands, France and Spain together, or twice the size of the state of Texas. Source of this estimate is the book Flotsametrics and the Floating World (2009) by the American oceanographer Curtis Ebbesmeyer. The size of the plastic soup gyres depends on the measured number of plastic items in relation to the surrounding ocean. Plastic soup is everywhere, also in lakes and rivers.

Hotspots

Is the concentration of plastic pollution highest in the gyres? Not necessarily. There are other places where the concentration of plastic is just as high or even higher. The plastic concentrates for other reasons than circulating currents. These places are called ‘hotspots’.

The Mediterranean Sea is one such hotspot. On the one hand, there is a permanent supply of plastic coming from the rivers that flow into the Mediterranean Sea and from the coastal cities. On the other hand, the connection to the Atlantic Ocean at the Strait of Gibraltar is so narrow that little plastic can escape into the Atlantic Ocean. In other words, the plastic that ends up in the Mediterranean Sea stays there. An average of 116,000 pieces of plastic per square kilometre has been reported.

Hotspots are places where, for various reasons, plastic concentrates. Apart from inland seas such as the Mediterranean Sea, Black Sea and Baltic Sea, these places include:

  • bays lined with large cities;
  • bays into which plastic floats and remains;
  • river mouths;
  • coastlines where industries are situated;
  • places or islands where different ocean currents congregate.