Marine debris, also known as marine litter, is human-created waste that has deliberately or accidentally been released in a lake, sea, ocean or waterway. Floating oceanic debris tends to accumulate at the center of gyres and on coastlines, frequently washing aground, when it is known as beach litter or tidewrack. Deliberate disposal of wastes at sea is called ocean dumping. Naturally occurring debris, such as driftwood, are also present.
With the increasing use of plastic, human influence has become an issue as many types of plastics do not biodegrade. Waterborne plastic poses a serious threat to fish, seabirds, marine reptiles, and marine mammals, as well as to boats and coasts. Dumping, container spillages, litter washed into storm drains and waterways and wind-blown landfill waste all contribute to this problem.
Types of debris
Researchers classify debris as either land- or ocean-based; in 1991, the United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution estimated that up to 80% of the pollution was land-based. More recent studies have found that more than half of plastic debris found on Korean shores is ocean-based. A wide variety of anthropogenic artifacts can become marine debris; plastic bags, balloons, buoys, rope, medical waste, glass bottles and plastic bottles, cigarette stubs, cigarette lighters, beverage cans, polystyrene, lost fishing line and nets, and various wastes from cruise ships and oil rigs are among the items commonly found to have washed ashore. Six pack rings, in particular, are considered emblematic of the problem. The US military used ocean dumping for unused weapons and bombs, including ordinary bombs, UXO, landmines and chemical weapons from at least 1919 until 1970. Millions of pounds of ordnance were disposed of in the Gulf of Mexico and off the coasts of at least 16 states, from New Jersey to Hawaii (although these, of course, do not wash up onshore, nor is the US the only country who has practiced this, safely dismantling and recycling explosives being a very dangerous and costly procedure).
Eighty percent of marine debris is plastic. Plastics accumulate because they typically do not biodegrade as many other substances do. They photodegrade on exposure to sunlight, although they do so only under dry conditions, as water inhibits photolysis. In a 2014 study using computers models, scientists from the group 5 Gyres, estimate 5.25 trillion pieces of plastic weighing 269,000 tons dispersed in oceans in similar amount in the Northern and Southern Hemispheres, and one-hundredth of them in particles in the scale of a sand-size.
Fishing nets left or lost in the ocean by fishermen – ghost nets – can entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs and other creatures. These nets restrict movement, causing starvation, laceration and infection, and, in animals that breathe air, suffocation.
Nurdles and plastic bags
Nurdles, also known as "mermaids' tears", are plastic pellets, typically under five millimetres in diameter, that are a major component of marine debris. They are a raw material in plastics manufacturing, and enter the natural environment when spilled. Weathering produces ever smaller pieces. Nurdles strongly resemble fish eggs.
Plastic waste has reached all the world's oceans. This plastic pollution harms an estimated 100,000 sea turtles and marine mammals and 1,000,000 sea creatures each year. Larger plastics (called "macroplastics") such as plastic shopping bags can clog the digestive tracts of these larger animals when consumed by them and can cause starvation through restricting the movement of food, or by filling the stomach and tricking the animal into thinking it is full. Microplastics on the other hand harm smaller marine life. Pelagic plastic pieces in the center of our ocean’s gyres for example outnumber live marine plankton, and are passed up the food chain to reach all marine life. A 1994 study of the seabed using trawl nets in the North-Western Mediterranean around the coasts of Spain, France and Italy reported mean concentrations of debris of 1,935 items per square kilometre. Plastic debris accounted for 77%, of which 93% was plastic bags.
Litter, made from diverse materials that are denser than surface water (such as glasses, metals and some plastics), have been found to spread over the floor of seas and open oceans, where it can become entangled in corals and interfere with other sea-floor life, or even become buried under sediment, making clean-up extremely difficult, especially due to the wide area of its dispersal compared to shipwrecks. Research performed by MBARI found items including plastic bags below 2000m depth off the west coast of North America and around Hawaii.
Sources of debris
An estimated 10,000 containers at sea each year are lost by container ships, usually during storms. One spillage occurred in the Pacific Ocean in 1992, when thousands of rubber ducks and other toys (now known as the "Friendly Floatees") went overboard during a storm. The toys have since been found all over the world, providing a better understanding of ocean currents. Similar incidents have happened before, such as when Hansa Carrier dropped 21 containers (with one notably containing buoyant Nike shoes). In 2007, MSC Napoli beached in the English Channel, dropping hundreds of containers, most of which washed up on the Jurassic Coast, a World Heritage Site.
In Halifax Harbour, Nova Scotia, 52% of items were generated by recreational use of an urban park, 14% from sewage disposal and only 7% from shipping and fishing activities. Around four fifths of oceanic debris is from rubbish blown onto the water from landfills, and urban runoff. In the 1987 Syringe Tide, medical waste washed ashore in New Jersey after having been blown from Fresh Kills Landfill. On the remote sub-Antarctic island of South Georgia, fishing-related debris, approximately 80% plastics, are responsible for the entanglement of large numbers of Antarctic fur seals.
Great Pacific Garbage Patch
Once waterborne, debris becomes mobile. Flotsam can be blown by the wind, or follow the flow of ocean currents, often ending up in the middle of oceanic gyres where currents are weakest. The Great Pacific Garbage Patch is one such example of this, comprising a vast region of the North Pacific Ocean rich with anthropogenic wastes. Estimated to be double the size of Texas, the area contains more than 3 million tons of plastic. In fact, patches may be large enough to be picked up by satellites. For example, when the Malaysian Flight MH370, disappeared in 2014, satellites were scanning the oceans surface for any sign of it, and instead of finding debris from the plane they came across floating garbage. The gyre contains approximately six pounds of plastic for every pound of plankton. The oceans may contain as much as one hundred million tons of plastic. Its estimated that each garbage patch in the ocean have up to one million tons of trash swirling around in them, sometimes extending down to around one hundred feet below the surface. Some items that have been extracted from these garbage patches are: a drum of hazardous chemicals, plastic hangers, tires, cable cords, a ton of tangled netting etc.
Over 40% of oceans are classified as subtropical gyres, a fourth of the planets surface area has become an accumulator of floating plastic debris.
Islands situated within gyres frequently have coastlines flooded by waste that washes ashore; prime examples are Midway and Hawaii. Clean-up teams around the world patrol beaches to attack this environmental threat.
Many animals that live on or in the sea consume flotsam by mistake, as it often looks similar to their natural prey. Bulky plastic debris may become permanently lodged in the digestive tracts of these animals, blocking the passage of food and causing death through starvation or infection. Tiny floating plastic particles also resemble zooplankton, which can lead filter feeders to consume them and cause them to enter the ocean food chain. In samples taken from the North Pacific Gyre in 1999 by the Algalita Marine Research Foundation, the mass of plastic exceeded that of zooplankton by a factor of six.
Toxic additives used in plastic manufacturing can leach into their surroundings when exposed to water. Waterborne hydrophobic pollutants collect and magnify on the surface of plastic debris, thus making plastic more deadly in the ocean than it would be on land. Hydrophobic contaminants bioaccumulate in fatty tissues, biomagnifying up the food chain and pressuring apex predators and humans. Some plastic additives disrupt the endocrine system when consumed; others can suppress the immune system or decrease reproductive rates.
The hydrophobic nature of plastic surfaces stimulates rapid formation of biofilms, which support a wide range of metabolic activities, and drive succession of other micro- and macro-organisms.
Concern among experts has grown since the 2000s that some organisms have adapted to live on floating plastic debris, allowing them to disperse with ocean currents and thus potentially become invasive species in distant ecosystems. Research in 2014 in the waters around Australia confirmed a wealth of such colonists, even on tiny flakes, and also found thriving ocean bacteria eating into the plastic to form pits and grooves. These researchers showed that "plastic biodegradation is occurring at the sea surface" through the action of bacteria, and noted that this is congruent with a new body of research on such bacteria. Their finding is also congruent with the other major research undertaken in 2014, which sought to answer the riddle of the overall lack of build up of floating plastic in the oceans, despite ongoing high levels of dumping. Plastics were found as microfibres in core samples drilled from sediments at the bottom of the deep ocean. The cause of such widespread deep sea deposition has yet to be determined.
Not all anthropogenic artifacts placed in the oceans are harmful. Iron and concrete structures typically do little damage to the environment because they generally sink to the bottom and become immobile, and at shallow depths they can even provide scaffolding for artificial reefs. Ships and subway cars have been deliberately sunk for that purpose.
Techniques for collecting and removing marine (or riverine) debris include the use of debris skimmer boats (pictured). Devices such as these can be used where floating debris presents a danger to navigation. For example, the US Army Corps of Engineers removes 90 tons of "drifting material" from San Francisco Bay every month. The Corps has been doing this work since 1942, when a seaplane carrying Admiral Chester W. Nimitz collided with a piece of floating debris and sank, costing the life of its pilot. Once debris becomes "beach litter", collection by hand and specialized beach-cleaning machines are used to gather the debris.
Elsewhere, "trash traps" are installed on small rivers to capture waterborne debris before it reaches the sea. For example, South Australia's Adelaide operates a number of such traps, known as "trash racks" or "gross pollutant traps" on the Torrens River, which flows (during the wet season) into Gulf St Vincent.
In lakes or near the coast, manual removal can also be used. Project AWARE for example promotes the idea of letting dive clubs clean up litter, for example as a diving exercise.
On the sea, the removal of artificial debris (i.e. plastics) is still in its infancy. However some projects have been started which used ships with nets (Kaisei and New Horizon) to catch some plastics, primarily for research purposes. Another method to gather artificial litter has been proposed by Boyan Slat. He suggested using platforms with arms to gather the debris, situated inside the current of gyres.
Another issue is that removing marine debris from our oceans can potentially cause more harm than good. Cleaning up micro-plastics could also accidentally take out plankton, which are the main lower level food group for the marine food chain and over half of the photosynthesis on earth. One of the most efficient and cost effective ways to help reduce the amount of plastic entering our oceans is to not participate in using singe use plastics, avoid plastic bottled drinks such as water bottles, use reusable shopping bags, and to buy products with reusable packaging.
Plastic-to-fuel conversion strategy
The Clean Oceans Project (TCOP) promotes conversion of the plastic waste into valuable liquid fuels, including gasoline, diesel and kerosene, using plastic-to-fuel conversion technology developed by Blest Co. Ltd., a Japanese environmental engineering company. TCOP plans to educate local communities and create a financial incentive for them to recycle plastic, keep their shorelines clean, and minimize plastic waste.
Laws and treaties
Ocean dumping is controlled by international law, including:
- The London Convention (1972) – a United Nations agreement to control ocean dumping
- MARPOL 73/78 – a convention designed to minimize pollution of the seas, including dumping, oil and exhaust pollution
In 1972 and 1974, conventions were held in Oslo and Paris respectively, and resulted in the passing of the OSPAR Convention, an international treaty controlling marine pollution in the north-east Atlantic Ocean. The Barcelona Convention protects the Mediterranean Sea. The Water Framework Directive of 2000 is a European Union directive committing EU member states to free inland and coastal waters from human influence. In the United Kingdom, the Marine and Coastal Access Act 2009 is designed to "ensure clean healthy, safe, productive and biologically diverse oceans and seas, by putting in place better systems for delivering sustainable development of marine and coastal environment".
United States law
In 1972, the United States Congress passed the Ocean Dumping Act, giving the Environmental Protection Agency power to monitor and regulate the dumping of sewage sludge, industrial waste, radioactive waste and biohazardous materials into the nation's territorial waters. The Act was amended sixteen years later to include medical wastes. It is illegal to dispose of any plastic in US waters.
Property law, admiralty law and the law of the sea may be of relevance when lost, mislaid, and abandoned property is found at sea. Salvage law rewards salvors for risking life and property to rescue the property of another from peril. On land the distinction between deliberate and accidental loss led to the concept of a "treasure trove". In the United Kingdom, shipwrecked goods should be reported to a Receiver of Wreck, and if identifiable, they should be returned to their rightful owner.
A large number of groups and individuals are active in preventing or educating about marine debris. For example, 5 Gyres is an organization aimed at reducing plastics pollution in the oceans, and was one of two organizations that recently researched the Great Pacific Garbage Patch. Heal the Bay is another organization, focusing on protecting California's Santa Monica Bay, by sponsoring beach cleanup programs along with other activities. Marina DeBris is an artist focusing most of her recent work on educating people about beach trash. Interactive sites like Adrift demonstrate where marine plastic is carried, over time, on the worlds ocean currents. On April 11, 2013 in order to create awareness, artist Maria Cristina Finucci founded The Garbage patch state at UNESCO –Paris in front of Director General Irina Bokova . First of a series of events under the patronage of UNESCO and of Italian Ministry of the Environment.
Forty-eight plastics manufacturers from 25 countries, are members of the Global Plastic Associations for solutions on Marine Litter, have made the pledge to help prevent marine debris and to encourage recycling.
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Media related to Marine debris at Wikimedia Commons
- United Nations Environment Programme Marine Litter Publications
- UNEP Year Book 2011: Emerging Issues in Our Global Environment Plastic debris, pages 21–34. ISBN 978-92-807-3101-9.
- NOAA Marine Debris Program – US National Oceanic and Atmospheric Administration
- Marine Debris Abatement – US Environmental Protection Agency
- Marine Research, Education and Restoration – Algalita Marine Research Foundation
- UK Marine Conservation Society
- Harmful Marine Debris – Australian Government
- The trash vortex – Greenpeace
- High Seas GhostNet Survey – US National Oceanic and Atmospheric Administration
- Social & Economic Costs of Marine Debris – NOAA Economics
- Tiny Plastic Bits Too Small To See Are Destroying The Oceans, Business Insider
- Ghost net remediation program - NASA, NOAA and ATI collaborating to detect ghost nets