Marine debris, also called marine litter, is solid waste made by humans that is intentionally or accidentally placed into the ocean or seas. Floating waste often gathers in the middle of large circular ocean currents and along coastlines, where it may wash up on beaches, known as beach litter or tidewrack. When people throw waste into the ocean on purpose, it is called ocean dumping. Naturally occurring materials, like driftwood and floating seeds, are also found in the ocean. Because of the growing use of plastic, human activity has become a major problem. Many types of plastics made from oil do not break down naturally, unlike natural materials. The largest type of plastic pollution in the ocean, making up about 10%, is fishing nets that are lost or thrown away. Plastic in the water harms fish, seabirds, marine reptiles, and marine mammals, as well as boats and coastal areas.

Dumping waste, spilled containers, litter that flows into storm drains and waterways, and trash blown from landfills all add to this issue. This pollution has caused serious problems, such as fishing nets trapping animals, large areas of the ocean filled with plastic waste, and harmful substances building up in the food chain.

To reduce marine debris and pollution, international laws and policies have been created. The United Nations included reducing ocean pollution in Sustainable Development Goal 14, which focuses on protecting life in the ocean. Some countries have made specific rules to address the issue based on their level of involvement. Additionally, non-profit groups, organizations, and government agencies are working to collect and remove plastic from the ocean. However, in 2017, the United Nations estimated that by 2050, there could be more plastic in the ocean than fish if major actions are not taken.

Types

Researchers divide debris into two groups: land-based or ocean-based. In 1991, the United Nations estimated that up to 80% of ocean pollution came from land, while the remaining 20% came from sudden events like storms or activities at sea. More recent studies show that over half of the plastic found on Korean shores came from the ocean.

Many man-made items can become marine debris. These include plastic bags, balloons, buoys, ropes, medical waste, glass and plastic bottles, cigarette stubs, lighters, beverage cans, polystyrene, lost fishing lines and nets, and waste from cruise ships and oil rigs. Six-pack rings are especially well-known examples of this problem.

The U.S. military used the ocean to dump unused weapons and bombs, including ordinary bombs, unexploded ordnance (UXO), landmines, and chemical weapons from 1919 to 1970. Millions of pounds of these items were dumped in the Gulf of Mexico and off the coasts of at least 16 states, from New Jersey to Hawaii. These items do not wash up on land, and other countries have also used ocean dumping.

About 80% of marine debris is plastic. Plastic accumulates because it does not break down easily like many other materials. Instead, it breaks down when exposed to sunlight, but only when it is dry. Water prevents this breakdown. In a 2014 study, scientists from the group 5 Gyres estimated that 5.25 trillion pieces of plastic weighing 269,000 tons were spread across the oceans, with similar amounts in the Northern and Southern Hemispheres.

Some materials and activities used in industrial work do not break down easily and remain in the environment for long periods. These activities include fishing, boating, and aquaculture, which can lose or throw away equipment, materials, or waste into the water or onto shorelines. This can include large items like fishing boats or small particles from foam lobster floats. A 2003 study in Charlotte County, New Brunswick, looked at the types, amounts, and effects of industrial marine debris near the coast. Materials like plastic or foam can break into tiny pieces that look like small sea creatures. Birds, whales, and fish may eat these pieces, which can block their stomachs or make them feel full, leading to starvation or death.

Ghost nets are fishing nets that have been lost, abandoned, or thrown away in the ocean, lakes, or rivers. These nets can get tangled on rocks or drift in the open sea. They can trap fish, dolphins, sea turtles, sharks, and other animals, including humans. The nets restrict movement, causing starvation, injuries, and suffocation. It is estimated that about 48 million tons of lost fishing gear are created each year, and these nets can remain in the ocean for many years before breaking apart.

A growing problem in the ocean is microplastics. Microplastics are tiny plastic pieces less than 5 millimeters wide. They are found in products like hand soaps, face cleansers, and other exfoliators. When these products are washed down the drain, the microplastics enter the ocean. Because they are so small, they often pass through wastewater treatment systems. These tiny plastics harm ocean life, especially filter feeders, which can accidentally eat them and become sick. Microplastics are hard to clean up because of their size, so people can help by choosing products that use safe exfoliating ingredients instead of plastic beads.

Plastic is used so widely that microplastics are now found throughout the ocean. They appear on beaches, in surface water, in the water column, and in deep-sea sediment. Microplastics are also found among other ocean particles, such as dead biological material and soil particles carried by rivers. The number of microplastics in an area often depends on how close it is to cities or how densely populated it is.

Marine debris is found on the floor of the Arctic Ocean. While many studies focus on plastic on coastlines, in surface waters, and in marine life that lives near the ocean’s surface, less is known about debris in the middle layers of the ocean or deeper areas. Research has used methods like bottom sampling, underwater robots, and submersibles to study deep-sea debris. These studies are often short-term and do not show long-term effects. However, research has shown that human activities have affected deep-sea debris, and plastic is often found in deep areas, especially near heavily populated regions like the Mediterranean.

Litter made of materials lighter than water, such as glass, metal, and some plastics, can spread across the ocean floor. This litter can entangle coral, harm other sea life, or become buried in sediment, making cleanup very difficult. Plastics that are heavier than water can sink when covered in tiny ocean plants or other particles. Natural ocean processes, like storms and underwater currents, also move debris. Underwater landforms can create currents that trap microplastics in certain areas.

In 2017, a database called the Deep-sea Debris database was made public. It includes 30 years of photos and samples from the ocean floor, collected from 5,010 dives using underwater robots and submersibles. Researchers counted 3,425 man-made items. The most common types were macro-plastic (33% of debris, with 89% being single-use items) and metal (26%). Plastic was found even in the Mariana Trench, at a depth of 10,898 meters, and plastic bags were found tangled in deep-sea communities near hydrothermal vents and cold seeps.

A garbage patch is a large area of ocean where plastic and other debris collect due to ocean currents and human pollution. These patches harm marine life, pollute the ocean with toxic chemicals, and cause environmental problems.

Environmental impacts

Not all human-made objects placed in the ocean are harmful. Iron and concrete structures usually do not harm the environment because they often sink to the ocean floor and stop moving. At shallow depths, these structures can even help create artificial reefs by providing a place for marine life to grow. Ships and subway cars have been intentionally sunk for this purpose.

Hermit crabs sometimes use pieces of trash found on beaches as a shell when they cannot find a real seashell of the right size.

Many sea animals that live on or in the ocean accidentally eat floating debris because it looks like their natural food. It is known that 1,288 marine species have eaten plastic waste, with fish being the largest group. Large pieces of plastic can get stuck in the stomachs of these animals, blocking their ability to eat and leading to starvation or illness. Small plastic particles floating on the ocean surface look like zooplankton, which can cause filter-feeding animals to eat them, allowing plastic to enter the ocean food chain. Plastic waste in the ocean can also harm the survival of fish and shellfish species by polluting the food chain.

In Kenya, the COVID-19 pandemic affected the amount of trash found on beaches, with about 55% of it being related to the pandemic. Although pandemic-related trash appeared on Kenyan beaches, it did not reach the ocean. The decrease in ocean trash during the pandemic may have been caused by beach closures and reduced movement, which likely prevented more trash from entering the water. In Hong Kong, the pandemic also had other effects, such as disposable masks being found on the beaches of Soko’s islands. This may be due to the increased production of medical supplies like masks and gloves during the pandemic, which led to more improper disposal of these items.

Removal

Techniques to collect and remove marine or riverine debris include using debris skimmer boats. These devices are used in areas where floating debris might harm ships. For example, the US Army Corps of Engineers removes 90 tons of "drifting material" from San Francisco Bay each month. This work has been ongoing since 1942, after a seaplane carrying Admiral Chester W. Nimitz collided with floating debris and sank, leading to the pilot's death. The Ocean Cleanup has created a vessel called the Interceptor to clean up riverine debris. Once debris reaches beaches, it is collected by hand or with special beach-cleaning machines.

Some projects encourage fishing boats to remove litter they accidentally catch while fishing. In other areas, "trash traps" are placed in small rivers to capture debris before it enters the ocean. For example, South Australia's Adelaide uses "trash racks" or "gross pollutant traps" on the Torrens River, which flows into Gulf St Vincent during the wet season.

In lakes or near coasts, manual removal is also used. Project AWARE promotes having dive clubs clean up litter during diving activities. Each year, a marine debris cleanup takes place in Scapa Flow, Orkney, organized by Ghost Fishing UK and funded by World Animal Protection and Fat Face Foundation.

Cleanup efforts can be hindered by poor cooperation between government levels and a mix of regulatory rules. For example, British Columbia has an estimated 1,600 abandoned boats in its waters. In 2019, Canada passed a law making it illegal to abandon a vessel, but enforcement is difficult because boat owners are not required to have licenses—licensing is managed by provincial governments. A non-profit group, Dead Boats Disposal Society, notes that lack of enforcement allows abandoned boats to sink, increasing cleanup costs and environmental harm from fuel, oil, and plastics.

Removing artificial debris, like plastics, is still in early stages. Some projects use ships with nets to collect plastics, mainly for research. Bluebird Marine System’s SeaVax, powered by solar and wind, had a shredder and storage area. The Sea Cleaners’ Manta ship uses a similar idea. The Ocean Cleanup’s Boyan Slat proposed using platforms with arms to gather debris in ocean gyres. The SAS Ocean Phoenix ship is similar in design.

In June 2019, Ocean Voyages Institute conducted a cleanup in the North Pacific Subtropical Convergence Zone, setting a record by removing over 84,000 pounds of polymer nets and plastic trash. In May/June 2020, the same group removed over 170 tons of consumer plastics and ghostnets in the same area. GPS trackers and satellite imagery help locate debris more efficiently.

Removing marine debris can sometimes cause more harm than good. For example, cleaning up microplastics might accidentally remove plankton, which are vital to the marine food chain and support half of Earth’s photosynthesis. One of the most effective ways to reduce ocean plastic is to avoid single-use plastics, choose reusable shopping bags, and buy products with reusable packaging.

Laws and treaties

The ocean is a shared resource for all people, so the negative effects of marine debris often affect others, not the person who created the waste. In the 1950s, the importance of government action to control marine pollution was recognized during the First Conference on the Law of the Sea.

Ocean dumping is managed by international laws, including:

• The London Convention (1972) – a United Nations agreement to control ocean dumping. This treaty had 22 rules outlining what countries must do. Three sections listed materials that cannot be dumped in the ocean, such as mercury compounds, lead, cyanides, and radioactive waste.
• MARPOL 73/78 – a treaty to reduce sea pollution, including dumping, oil spills, and exhaust pollution. The original MARPOL treaty did not address dumping from ships, but it was updated in 1978 to include rules for ships.
• UNCLOS – signed in 1982 and became active in 1994, this United Nations treaty focused on protecting the entire ocean, not just areas near coasts. It required limits on pollution, including pollution from land.

One of the first laws against dumping was Australia’s Beaches, Fishing Grounds and Sea Routes Protection Act 1932. This law forbade throwing garbage, rubbish, ashes, or organic waste into the ocean in Australian waters without permission from the federal government. It also required permission for scuttling (intentionally sinking a ship). The law was created after large amounts of garbage washed up on Sydney and Newcastle beaches from ships outside local government control. This law was replaced in 1981 by the Environment Protection (Sea Dumping) Act, which followed the London Convention.

In 1972 and 1974, meetings in Oslo and Paris led to the OSPAR Convention, an international treaty to control pollution in the north-east Atlantic Ocean. The Barcelona Convention protects the Mediterranean Sea. The Water Framework Directive of 2000 is a European Union rule requiring member countries to reduce human impact on inland and coastal waters. In the United Kingdom, the Marine and Coastal Access Act 2009 aims to keep oceans and seas clean, safe, and biologically diverse by improving management of marine areas. In 2019, the EU Parliament approved a ban on single-use plastic items like straws, cutlery, plates, drink containers, polystyrene food containers, plastic stirrers, and plastic bags. This law will begin in 2021.

In the United States, pollution has caused problems such as low-oxygen zones, harmful algae blooms, and endangered species. In 1972, the U.S. Congress passed the Ocean Dumping Act, giving the Environmental Protection Agency authority to monitor and control the disposal of sewage sludge, industrial waste, radioactive waste, and biohazardous materials in U.S. territorial waters. The law was updated 16 years later to include medical waste. It is illegal to throw any plastic into U.S. waters.

Laws related to property, admiralty, and the sea may apply when lost, misplaced, or abandoned items are found at sea. Salvage law rewards people who rescue others’ property from danger. On land, the difference between intentional and accidental loss led to the idea of a "treasure trove." In the United Kingdom, shipwrecked goods must be reported to a Receiver of Wreck, and if identifiable, they must be returned to their rightful owner.

Activism

Many groups and people work to stop or teach others about ocean trash. For example, 5 Gyres is an organization that helps reduce plastic pollution in the oceans. This group studied the Great Pacific Garbage Patch, a large area of ocean plastic. Heal the Bay is another group that protects California’s Santa Monica Bay by organizing beach cleanups and other activities. Marina DeBris is an artist who creates art to teach people about trash on beaches. Websites like Adrift show how ocean plastic moves over time with ocean currents.

On April 11, 2013, artist Maria Cristina Finucci created the Garbage Patch State at UNESCO in Paris in front of Director General Irina Bokova. This event was the first in a series supported by UNESCO and the Italian Ministry of the Environment.

Forty-eight companies from 25 countries are part of the Global Plastic Associations. These companies have promised to help stop ocean trash and support recycling.

Ocean trash is a big problem that happens everywhere, not just near coasts. Plastic waste from inland areas comes from two main sources: regular trash and materials from open dumps and landfills. This trash can blow or wash into rivers, lakes, and other waterways, eventually reaching the ocean. While cleaning up oceans and coasts is important, it is also necessary to address plastic waste from inland and landlocked areas.

To reduce trash in waterways, these actions can help:
– Improve waste transportation by using closed containers for storage and shipping.
– Stop open waste areas near waterways.
– Encourage the use of refuse-derived fuels. Used plastic that is not valuable is often not recycled and may end up in the ocean. Turning this plastic into fuel for power plants allows it to be used again.
– Increase the amount of plastic that is recovered. In 2012, the United States produced 11.46 million tons of plastic waste, but only 6.7% was recovered.
– Use Extended Producer Responsibility strategies to make companies responsible for managing their products and packaging when they become waste. Encourage the design of reusable products to protect the environment.
– Ban the use of cigarette filters and create a deposit system for e-cigarettes, similar to systems for propane canisters.

People can help reduce ocean trash by using fewer single-use plastics, avoiding products with microbeads, and joining beach or river cleanups.