Search teams scouring the Indian Ocean for pieces of the missing Malaysian Airlines plane thought they had promising clues earlier this week.

Turns out, they were only finding bits of abandoned fishing equipment.

Last week, a French satellite identified an apparent debris field containing 122 objects. That, too, was inconclusive.

These false leads are not only heartbreaking for the families of those who were on board the missing airliner MH370, but give an indication of the vast amount of junk floating in the open seas.

"Basically, the world's oceans are plasticized," says Marcus Eriksen, executive director of the 5 Gyres Institute, a conservation group that researches the amount of plastic pollution in the planet's seas.

Because of the difficulty of measuring, there are varying estimates of just how much trash is in our oceans.

Oceanographer Charles Moore, who works with the Algalita Marine Research Institute in Long Beach, Calif., estimates there could be 200 million tonnes of plastic debris floating in the seas. This calculation is based on the belief that 2.5 per cent of the world's plastic lands in the ocean.

Eriksen says there are currently no reliable estimates of the amount of ocean junk worldwide, and he is hoping that a coming report by 5 Gyres will be the first reliable global estimate.

It's based on 24 expeditions over the course of six years by six colleagues, and it found that there are nearly 5.25 trillion particles of plastic trash in the oceans, weighing half a million tonnes.

"You're going to find some lightbulbs, fluorescent tubes, some wood, some coconuts and seeds, but by and large, it's mostly plastic," says Eriksen.

These estimates don't include the detritus that's sitting at the bottom of the oceans, which, as he says, is "virtually unknown."

'Deathtraps for marine animals'

One major constituent of ocean junk is fishing gear such as nets and buoys, says Eric Galbraith, an assistant professor in the department of earth and planetary science at McGill University.

"Floating nets often come adrift, and cause particularly bad problems because they can be long-lived deathtraps for marine animals," he says.

The garbage found at sea comes from a variety of sources. Some of it is deposited in rivers that empty into larger bodies of water, while some is drawn into the ocean during natural disasters like tsunamis.

This debris is pushed around by ocean currents. While trash can be found all over the high seas, it has become especially prominent in the five gyres -- large systems of rotating ocean currents that exist between the continents.

They include the North Atlantic and South Atlantic gyres, the North Pacific and South Pacific gyres and the Indian Ocean gyre, which is just west of the area where the Malaysia Airlines plane is thought to have gone down.

Due to global wind patterns, air continually pushes the surface water of the gyres, and the plastic in it, towards the centres of the ocean basin. But since plastic floats, it just continually returns to the top, and remains more or less in place.

"The gyres concentrate the garbage at the surface, just like a filter in a bathtub drain concentrates the hairs from a bath," says Galbraith.

The most infamous example of this is what's known as the Great Pacific Garbage Patch. Located between Hawaii and California in the middle of the North Pacific gyre, it was first described by Charles Moore in an article for Natural History magazine in 1993.

In photographs, it's a roiling soup of plastic bottles, caps, wrappers and other disposable goods. According to National Geographic magazine, scientists have gathered up to 750,000 bits of plastic in a square kilometre of that patch.

Taking out the trash

A great deal of garbage is also dumped directly into the oceans by cruise and cargo ships.

The United Nations Convention on the Law of the Sea (1982) encourages nations to take "all measures necessary to prevent, reduce, and control pollution of the marine environment from any source."

Galbraith says that for a long time, there was a general understanding that unless it was chemical waste, it was fine to toss junk from ships into international waters.

There are now stricter rules in place. In 2012, the International Maritime Organization adopted measures to prohibit the disposal of plastics anywhere in the sea. "But it takes time to change old habits," says Galbraith.

There is also the problem of accidental garbage, like when turbulent weather blows shipping containers overboard, which led to the famous release of 29,000 plastic ducks in the Pacific Ocean in January 1992.

The World Shipping Council says about 350 containers are lost at sea each year, although non-industry observers estimate the annual rate to be much higher.

"There are a lot of container ships that carry material goods all over the planet, and it turns out that it's cheaper to allow a certain amount of loss off those ships than it is to make sure that they're absolutely storm-proof," says Galbraith.

While there has been international debate about how to clean up the trash-strewn corners of the sea, Eriksen says that the very nature of the plastic problem makes it almost impossible.

It's been estimated that 93 per cent of those plastic particles bobbing in the seas are about the size of a grain of rice or smaller.

"That really makes clean-up very impractical," says Eriksen. "You can't get all these trillions of small particles out of the ocean."

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  • A Chinese relative of passengers on the missing Malaysia Airlines flight MH370 holds a candle as she takes part in a prayer service at the Metro Park Hotel in Beijing on April 8, 2014. (WANG ZHAO/AFP/Getty Images)

  • A woman lights a candle as Chinese relatives of passengers on the missing Malaysia Airlines flight MH370 take part in a prayer service at the Metro Park Hotel in Beijing on April 8, 2014. (WANG ZHAO/AFP/Getty Images)

  • A Chinese relative of passengers on the missing Malaysia Airlines flight MH370 holds a candle as he takes part in a prayer service at the Metro Park Hotel in Beijing on April 8, 2014. (WANG ZHAO/AFP/Getty Images)

  • Royal New Zealand Air Force (RNZAF) Tactical Coordinator Brent Collier (C) briefs the crew aboard a P3 Orion maritime search aircraft before take-off towards the southern Indian Ocean looking for debris from missing Malaysian Airlines flight MH370 at RAAF Base Pearce on April 11, 2014 in Perth, Australia. (Richard Polden - Pool/Getty Images)

  • Royal New Zealand Air Force (RNZAF) Co Pilot squadron Leader Brett McKenzie (L) and Flight Engineer Trent Wyatt sit in the cockpit aboard a P3 Orion maritime search aircraft as it flies over the southern Indian Ocean looking for debris from missing Malaysian Airlines flight MH370 on April 11, 2014. (Richard Polden - Pool/Getty Images)

  • A graphic of the area being searched for missing Malaysia Airlines flight MH370, is displayed during a media conference involving Angus Houston, head of the Joint Agency Coordination Centre in Perth on April 9, 2014. (GREG WOOD/AFP/Getty Images)

  • Crew members look out the cockpit windows of a RNZAF P3 Orion during search operations for wreckage and debris of missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean, near the coast of Western Australia on April 4, 2014. (Nick Perry/AFP/Getty Images)

  • An unidentified object is photographed from a monitor onboard a RNZAF P3 Orion during search operations for wreckage and debris of missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • An observer watches as a smoke flare is deployed to mark an unidentified object spotted from a RNZAF P3 Orion during search operations for wreckage and debris of missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • SGT Sean Donaldson prepares to deploy a smoke marker onboard a RNZAF P3 Orion during search operations for wreckage and debris of missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • An observer looks out a window onboard a RNZAF P3 Orion during search operations for missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • SGT Adam Coats gets some rest onboard a RNZAF P3 Orion after they completed almost four hours of search operations for missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • Wing commander Rob Shearer, captain of the RNZAF P3 Orion (L), and SGT Sean Donaldson look out the cockpit windows during search operations for missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • Operators monitor TAC stations onboard a RNZAF P3 Orion during search operations for wreckage and debris of missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • Flight LT Stephen Graham monitors a TAC station onboard a RNZAF P3 Orion during search operations for wreckage and debris of missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • Chinese relatives of passengers on the missing Malaysia Airlines flight MH370 rest before a meeting at a hotel in Beijing on April 3, 2014. (WANG ZHAO/AFP/Getty Images)

  • Chinese relatives of passengers on the missing Malaysia Airlines flight MH370 pray after a meeting in a prayer room at the Metro Park Hotel in Beijing on April 4, 2014. (WANG ZHAO/AFP/Getty Images)

  • Wing commander Rob Shearer, captain of the RNZAF P3 Orion, reads through his notes before reaching the search area for missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • SGT Sean Donaldson prepares to deploy a smoke marker onboard a RNZAF P3 Orion during search operations for wreckage and debris of missing Malaysia Airlines Flight MH370 in the Southern Indian Ocean on April 4, 2014, near Australia. (Nick Perry - Pool/Getty Images)

  • This picture taken on March 24, 2014 shows crew members on board an RAAF AP-3C Orion crossing the coast of Perth, having just completed an 11 hour search mission for missing Malaysia Airways flight MH370 before landing at the RAAF Pearce airbase in Perth.(RICHARD WAINWRIGHT/AFP/Getty Images)

  • Japan Maritime Self-Defense Force AP-3C Orions sit on the tarmac after arriving back at RAAF Base Peace after continuing the search for debris or wreckage of the missing Malaysia Airlines Flight MH370, at Bullsbrok on March 26, 2014. (ROB GRIFFITH/AFP/Getty Images)

  • Flying Officer Stuart Doubleday (L) and Warrant Officer Michael Makin sit in the cockpit of a Royal Australian Air Force AP-3C Orion aircraft searching for missing Malaysian Airlines flight MH370 over the southern Indian Ocean on March 27, 2014 off the coast of Perth, Australia. (Michael Martina - Pool/Getty Images)

  • Excess fuel is dumped from a nozzle protruding from the left wing of a Royal Australian Air Force AP-3C Orion aircraft before landing, after their mission searching for missing Malaysian Airlines flight MH370 over the southern Indian Ocean was aborted, on March 27, 2014 off the coast of Perth, Australia. (Michael Martina - Pool/Getty Images)

  • Flight Lieutenant Jayson Nichols looks at a map as he flies aboard a Royal Australian Air Force AP-3C Orion aircraft searching for missing Malaysian Airlines flight MH370 over the southern Indian Ocean on March 27, 2014 off the coast of Perth, Australia. (Michael Martina - Pool/Getty Images)

  • Crew members aboard a Royal Australian Air Force AP-3C Orion aircraft observe navigation maps as they search for missing Malaysian Airlines flight MH370 over the southern Indian Ocean on March 27, 2014 off the coast of Perth, Australia. (Michael Martina - Pool/Getty Images)

  • A Royal Australian Air Force AP-3C Orion returns to RAAF Base Pearce after continuing the search for debris or wreckage of the missing Malaysia Airlines Flight MH370 on March 26, 2014 in Perth, Australia. (Rob Griffith - Pool/Getty Images)

  • RAAF Flight Engineer Ron Day keeps watch for debris from a AP-3C Orion during a search mission for missing Malaysia Airline flight MH370 in the Southern Indian Ocean on March 26, 2014. (Paul Kane/AFP/Getty Images)

  • This picture taken on March 24, 2014 shows a crew member of an RAAF AP-3C Orion aircraft loading a sono buoy that will mark the location of any wreckage found whilst searching for missing Malaysia Airways flight MH370 over the Indian Ocean. (RICHARD WAINWRIGHT/AFP/Getty Images)

  • This picture taken on March 24, 2014 shows crew members on board an RAAF AP-3C Orion crossing the coast of Perth, having just completed an 11 hour search mission for missing Malaysia Airways flight MH370 before landing at the RAAF Pearce airbase in Perth. (RICHARD WAINWRIGHT/AFP/Getty Images)

  • This picture taken on March 24, 2014 shows a view of the bad weather and visibility from a low flying RAAF AP-3C Orion aircraft whilst searching for missing Malaysia Airways flight MH370 over the Indian Ocean. (RICHARD WAINWRIGHT/AFP/Getty Images)

  • Aircrew look out of a window of a Royal Australian Air Force AP-3C Orion from RAAF base Pearce on assignment to Southern Indian Ocean to commence a search for possible debris from the Malaysian Airlines flight MH370 on March 24, 2014 in Perth, Australia. (Bohdan Warchomij - Pool/Getty Images)

  • Members of Japan's disaster relief team wave off a Japan Maritime Self-Defence Force Lockheed P-3C Orion aircraft as it takes off from RAAF base Pearce in Bullsbrook, 35 kms north of Perth, on March 24, 2014 to search for missing Malaysia Airlines flight MH370. (JASON REED/AFP/Getty Images)

  • Japanese Maritime Self Defence Force personnel walk from the tarmac as a P-3C Orion prepares to depart from the RAAF base Pearce in Bullsbrook, 35 kms north of Perth on March 24, 2014 to depart to search for missing Malaysia Airlines flight MH370 over the southern Indian Ocean. (Paul Kane/AFP/Getty Images)

  • Aircrew walk on the wing of a Japanese Air Force AP-3C Orion after it landed at RAAF Pearce Base to join the search for missing Malaysian Airlines flight MH370 on March 23, 2014 in Perth, Australia. (Rob Griffith-Pool/Getty Images)

  • A Japanese Air Force AP-3C Orion, helping with the search of missing Malaysia Airlines flight MH370, arrives at RAAF base Pearce in Bullsbrook, 35 kms north of Perth on March 23, 2014. (ROB GRIFFITH/AFP/Getty Images)

  • Japan's Maritime Self-Defense Force Personnel wave to their colleagues on a P3C aircraft before taking off for Australia to join the search operation for the missing Malaysia Airlines flight MH370 at the Royal Malaysian Air Force base in Subang, outside Kuala Lumpur on March 23, 2014. (MOHD RASFAN/AFP/Getty Images)

  • Japan's Maritime Self-Defense Force Personnel pose for pictures near a PC3 aircraft before taking off for Australia to join the search operation for the missing Malaysia Airlines flight MH370 at the Royal Malaysian Air Force base in Subang, outside Kuala Lumpur on March 23, 2014. (MOHD RASFAN/AFP/Getty Images)

  • A member of Japan's Maritime Self-Defense Force writes down coordinates before taking off on a PC3 aircraft for Australia to join the search operation for the missing Malaysia Airlines flight MH370 at the Royal Malaysian Air Force base in Subang, outside Kuala Lumpur on March 23, 2014. (MOHD RASFAN/AFP/Getty Images)

  • Flight Lieutenant Jason Nichols on board a Royal Australian Air Force AP-3C Orion, takes notes as they search for missing Malaysian Airlines flight MH370 debris or wreckage on March 22, 2014 in Southern Indian Ocean, off the west coast of Australia. (Rob Griffith-Pool/Getty Images)

  • A Royal Australian Air Force AP-3C Orion flies past the HMAS Success as they search for missing Malaysia Airlines flight MH370 debris or wreckage in the southern Indian Ocean on March 22, 2014. (ROB GRIFFITH/AFP/Getty Images)

  • Australian Prime Minister Tony Abbott bids farewell to the Malaysian Prime Minister's wife, Datin Sri Rosmah Mansor, after her visit to Perth during the search for missing Malaysia Airlines flight MH370, at Perth International airport, April 3, 2014. (Paul Kane - Pool/Getty Images)

  • A Chinese relative (R) of passengers on the missing Malaysia Airlines flight MH370 waits for the new information before a meeting at a hotel in Beijing on April 3, 2014. (WANG ZHAO/AFP/Getty Images)

  • Malaysian Prime Minister Najib Razak waves farewell prior to boarding his aircraft at Perth International airport after visiting Australia during the search for missing Malaysia Airlines flight MH370 on April 3, 2014. (Paul Kane - Pool/Getty Images)

  • Malaysian Prime Minister Najib Razak (L) and Australian Prime Minister Tony Abbott hold a bilateral meeting on the search for Malaysia Airlines flight MH370 at the Commonwealth Parliament Offices at Exchange Plaza in Perth on April 3, 2014. (RICHARD WAINWRIGHT/AFP/Getty Images)

  • A Chinese relative of passengers on the missing Malaysia Airlines flight MH370 watches television as he waits for new information at a hotel in Beijing on April 3, 2014. (WANG ZHAO/AFP/Getty Images)

  • A Japan Orion aircraft prepares to leave Pearce Airbase at Bullsbrook, 35 km north of Perth, on April 3, 2014, to continue the search for missing Malaysian Airlines Flight MH370. (GREG WOOD/AFP/Getty Images)