Marine plastic pollution

Marine plastic pollution is a type of marine pollution by plastics, ranging in size from large original material such as bottles and bags, down to microplastics formed from the fragmentation of plastic material. Marine debris is mainly discarded human rubbish which floats on, or is suspended in the ocean. Eighty percent of marine debris is plastic.^[1][2] Microplastics and nanoplastics result from the breakdown or photodegradation of plastic waste in surface waters, rivers or oceans. Recently, scientists have uncovered nanoplastics in heavy snow, more specifically about 3,000 tons that cover Switzerland yearly.^[3]

It is estimated that there is a stock of 86 million tons of plastic marine debris in the worldwide ocean as of the end of 2013, assuming that 1.4% of global plastics produced from 1950 to 2013 has entered the ocean and has accumulated there.^[4] Global consumption of plastics is estimated to be 300 million tonnes per year as of 2022, with around 8 million tonnes ending up in the oceans as macroplastics.^[5][6] Approximately 1.5 million tonnes of primary microplastics end up in the seas. Around 98% of this volume is created by land-based activities, with the remaining 2% being generated by sea-based activities.^[6][7][8] It is estimated that 19–23 million tonnes of plastic leaks into aquatic ecosystems annually.^[9] The 2017 United Nations Ocean Conference estimated that the oceans might contain more weight in plastics than fish by the year 2050.^[10]

A woman and a boy collecting plastic waste at a beach during a cleanup exercise

Oceans are polluted by plastic particles ranging in size from large original material such as bottles and bags, down to microplastics formed from the fragmentation of plastic material. This material is only very slowly degraded or removed from the ocean so plastic particles are now widespread throughout the surface ocean and are known to be having deleterious effects on marine life.^[11] Discarded plastic bags, six-pack rings, cigarette butts and other forms of plastic waste which finish up in the ocean present dangers to wildlife and fisheries.^[12] Aquatic life can be threatened through entanglement, suffocation, and ingestion.^[13][14][15] Fishing nets, usually made of plastic, can be left or lost in the ocean by fishermen. Known as ghost nets, these entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs, and other creatures, restricting movement, causing starvation, laceration, infection, and, in those that need to return to the surface to breathe, suffocation.^[16] There are various types of ocean plastics causing problems to marine life. Bottle caps have been found in the stomachs of turtles and seabirds, which have died because of the obstruction of their respiratory and digestive tracts.^[17] Ghost nets are also a problematic type of ocean plastic as they can continuously trap marine life in a process known as "ghost fishing".^[18]

The 10 largest emitters of oceanic plastic pollution worldwide are, from the most to the least, China, Indonesia, Philippines, Vietnam, Sri Lanka, Thailand, Egypt, Malaysia, Nigeria, and Bangladesh,^[19] largely through the Yangtze, Indus, Yellow River, Hai, Nile, Ganges, Pearl River, Amur, Niger, and Mekong, and accounting for "90 percent of all the plastic that reaches the world's oceans".^[20][21] Asia was the leading source of mismanaged plastic waste, with China alone accounting for 2.4 million metric tons.^[22]

Plastics accumulate because they do not biodegrade in the way many other substances do. They will photodegrade on exposure to the sun, but they do so properly only under dry conditions, and water inhibits this process.^[23] In marine environments, photodegraded plastic disintegrates into ever-smaller pieces while remaining polymers, even down to the molecular level. When floating plastic particles photodegrade down to zooplankton sizes, jellyfish attempt to consume them, and in this way the plastic enters the ocean food chain.^[24][25]

Solutions to marine plastic pollution, along with plastic pollution within the whole environment will be intertwined with changes in manufacturing and packaging practices, and a reduction in the usage, in particular, of single or short-lived plastic products. Many ideas exist for cleaning up plastic in the oceans including trapping plastic particles at river mouths before entering the ocean, and cleaning up the ocean gyres.^[2]