When you hear the word “marine debris”, the first things that come to mind may be various kinds of trash floating about in the ocean, such as shampoo bottles, flip-flops, plastic bottles, plastic bags, and so on.
Marine debris is the artificial waste that exists in the ocean or shore environment for any reason and that does not decompose easily.
Marine debris can also come in huge sizes, such as wrecked ships and giant nets which were once used as fishing gear, or even vehicles and freight containers.
Ships, vehicles, and motorbikes that were carried away by a tsunami are also classified as marine debris.
Generally speaking, marine debris consists of such materials as paper, wood, fabric, metal, glass, ceramic, rubber, and plastic（UNEP 2005）. Plastic is the most commonly found material among marine debris, and most plastic waste comes from consumer products.
When you take a walk along the shore, you will frequently see various kinds of plastic marine debris, such as plastic bags, food containers, fishing lines, plastic bottles, cigarette ends, and so on.
Approximately 80% (sometimes 100%!) of marine debris that is seen on the ocean surface, the seashore and sea floor consists of plastic waste（UNEP and GRID-Arendal 2016）.
Incidentally, at the top of the list of plastic waste, in other words the main source of marine debris, are plastics used for wrapping or packaging, such as food containers, plastic bags, plastic bottles, detergent containers, Styrofoam packaging, etc.
Most of these are single-use plastics that are thrown away after being used just once. These single-use plastics comprise only 30-40% of all of the plastic produced, but they account for more than 60% of plastic waste（Plastic Europe 2015, American Chemistry Council 2015, Velis 2014）.
All in all, single-use plastics are the biggest main source of marine debris（Hopewell et a. 2009）.
Once plastic waste reaches the ocean, it will be carried for quite a long distance, spreading and entering every part of the ocean, from its surface to the bottom of the deep sea and even into the icebergs of the Arctic.
The number of marine animals that accidentally eat plastic waste and die, such as whales and sea turtles, is increasing horrendously, as is the number of marine animals that become tangled in plastic waste, which leads to their suffocation and death.
Plastic waste in the sea will decompose and disintegrate over time and eventually turn into smaller pieces. These tiny pieces of plastic waste are called microplastics.
These tiny microplastics are found everywhere in the ocean and have a worrying impact on the ecosystem.
For example, microplastics absorb harmful chemical substances, such as DDT and PCBs, very well. They are then eaten by small marine animals such as zooplankton, shellfish and sardines, sneaking into the food chain and eventually coming back to become our meal.
Currently, research in microplastics has just begun and we are still not sure how much impact they are having on ecosystems and on our own health.