Clues emerge in 'missing' ocean plastics conundrum

Of the between 4-12 million tonnes that enter the oceans each year, just 250 thousand tonnes—less than one percent—stays on the
Of the between 4-12 million tonnes that enter the oceans each year, just 250 thousand tonnes—less than one percent—stays on the surface

It's a puzzle that has perplexed scientists for years: humanity dumps millions of tonnes of plastics into the world's oceans annually, yet only a tiny fraction remains visible on the surface.

Now an international team of researchers believe they may be closer to determining where Earth's "missing plastics" end up, using an unprecedented global effort to track and draw down one of the most polluting materials ever invented.

As images of plastic-clogged beaches and swirling gyres of detritus bobbing on the high seas are prompting governments and cities to curb their throwaway culture, a growing body of evidence suggests a deeper problem of plastic permeating all ocean depths.

Of the between 4-12 million tonnes that enter the oceans each year, just 250 thousand tonnes are thought to stay at the surface. Overall, more than 99 percent of plastics dumped at sea over several decades are currently unaccounted for.

As plastics degrade through erosion, UV light and microbial decay, their density changes, putting them at the mercy of ocean currents—and, once they get pulled lower in the water, much harder for experts to track.

"It's quite difficult to decide where it all is because there are so many processes at work," Alethea Mountford, from Newcastle University's School of Natural and Environmental Sciences, told AFP.

"Even plastic at the surface can sink down and go back up again—it's moving between different possible sinks in different areas of the ocean at any time."

In a potential breakthrough, Mountford used a computer model of ocean currents for plastics of three different densities to project where most of the world's fragments collect once they start to sink.

The model showed significant build ups at depths varying thousands of metres in the Mediterranean Sea, Indian Ocean and the waters surrounding Southeast Asia.

Much of the plastic ends up on the seabed—as researchers outlined earlier this year in a separate study that found microplastic fibres in the guts of tiny shrimp that live at the bottom of the Mariana Trench—the deepest place on Earth.

While Mountford stressed that her research was preliminary, the results could help focus investigation on the ocean areas identified and enable better studies of the damage plastics cause to marine life.

Plastic pollution of the oceans
World map showing marine areas where plastic rubbish and microplastics are collected by circular currents.

Coastal collection

Mountford's work draws on that of Eric van Sebille, associate professor in Oceanography and Climate Change at Utrecht University in the Netherlands.

He said that most plastic pollution research had traditionally focused on the fragments that stay on the surface—and with good reason.

"We know the most about the garbage patches so it makes sense to focus on them and if you look at the impact the surface plastic probably does have the most because most organisms live there," he told AFP.

"But if you want to understand the complete problem then we need to get a deeper view."

Van Sebille's current research is based on the fact that plastic pollution is now so prolific that monitoring the waste fragments themselves can provide valuable insight into how oceans circulate.

His hunch—which should be borne out as modelling gets more sophisticated—is that the vast majority of plastics dumped in the oceans wash back ashore. This would account for the huge disparity in the volume entering the oceans and the smaller amounts that can be seen today.

"Plastic gets out of a river, it stays within the coastal zone for a while and it has the opportunity to wash back to shore and quite a lot of it might do that," he said.

Van Sebille added that while the problem of plastic pollution today may seem insurmountable, focusing clean up efforts in coastal areas could save much more widespread plastic contamination in the long-run.

"More and more we think that plastic spends a lot of time in that coastal zone so you don't need to do that much clean up to get rid of 10 million tonnes," he said.

Plastics found on glacier

In a series of studies on plastic waste unveiled Tuesday at the European Geosciences Union in Vienna, one paper showed plastic contamination on the Forni Glacier, a vast body of frozen water high up the Italian Alps.

A team of Italian experts found between 28-74 items per kilogramme of sediment analysed—meaning that the entire glacier is home to 131-162 million plastic items.

"From marine trenches to glaciers we have now found microplastics," said Roberto Sergio Azzoni, from the University of Milan, who led the research.

Explore further

Plastic found in deepest ocean animals

© 2019 AFP

Citation: Clues emerge in 'missing' ocean plastics conundrum (2019, April 9) retrieved 18 July 2019 from
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User comments

Apr 09, 2019
It should be up to governmental officials to encourage the consumer public to recycle plastics of all types - hard and soft - instead of tossing such plastics in the trash. Such recycled plastics can be melted down and made into other plastic forms, over and over. The same with different metals and cardboard.

Apr 09, 2019
The piece we are badly in need of is technology that can take a mixed stream of plastics and separate it/break it down into usable feed stocks. Ideally, it would be able to do this while excluding contaminants like paper, metals, etc. As it is, I take plastic bags back to the store for recycling (except those that become dog poop bags!) My hauler only recycles plastics in the shape of bottles/jars. I don't know what that is about. It leave out all sorts of fine PETE used for product packaging, etc.

Apr 09, 2019
Most of the plastic in the oceans (90% or more) is coming from poor, underdeveloped countries. The best way to reduce most of the plastic in the oceans is to create incentives for those countries to prevent plastic from getting into waterways and the ocean.

Apr 09, 2019
It's actually a myth that most plastic is recyclable. It has been pushed by plastics industries and cheap crap manufacturers for decades. Only a few types of plastic can actually be recycled in an economical way, and most of the rest is just baled and sent to 3rd world countries where it will pollute the planet just as hard as if it had just been tossed in a landfill at home.

Apr 09, 2019
Ever seen the plastic in Asian rivers? It's so pervasive, you often can't SEE water. It's time to force them to comply with reasonable pollution laws or we start starving them out.

Apr 10, 2019
There are many types of bacteria for which plastic is food. The difficulty is that these bacteria can only attach and degrade plastic at the surface or ends of the fibers.

But as the plastic degrades physically into smaller and smaller pieces it becomes easier to be eaten.

That is probably where a great deal of the plastic has gone.

Apr 10, 2019
Such recycled plastics can be melted down and made into other plastic forms, over and over
All you have to do with any one of SEU/pirouette/pussycat_eyes_/racistblackguy et al posts is check it and discover made-up bullshit.

"When different types of plastics are melted together, they tend to phase-separate, like oil and water, and set in these layers. The phase boundaries cause structural weakness in the resulting material, meaning that polymer blends are useful in only limited applications. The two most widely manufactured plastics, polypropylene and polyethylene, behave this way, which limits their utility for recycling."

"The same piece of plastic can only be recycled about 2-3 times before its quality decreases to the point where it can no longer be used. Additionally, each time plastic is recycled, additional virgin material is added to help "upgrade" its quality"

-Most plastic is not recyclable for a number of reasons.

No matter what bullshit artists say.

Apr 10, 2019
Such recycled plastics can be melted down and made into other plastic forms, over and over.

Not really. There are tens of thousands of different plastic formulations with different properties, and keeping them separate through the waste cycle is a practical impossibility. Many plastics aren't even thermoplastic - you can't re-melt them - and separating any contaminants is a process that requires infeasible amounts of energy.

Some plastics can be recycled to some effect, but most of them are just better off disposed in a waste incinerator. If you found a way to decompose them back to oil using a simple process that doesn't use expensive catalysts or tons of energy, you'd have found the holy grail of petrochemistry.

Apr 10, 2019
There are many types of bacteria for which plastic is food.

Except inorganic plastics like silicone, or poisonous plastics like teflon, or the fillers like chalk and kaolin, talc, titanium dioxide, silica... which make the microscopic plastic particles like eating sand.

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