Plastic to become the fossil marker of the Anthropocene

The most important thing that came out of the last G7 summit in Canada was Donald Trump's stunt of slamming the door in the face of his allies. What was less noticed was the disagreement on a subject on which the scientific community keeps alerting us: plastic pollution of the oceans. The world's leaders have failed to agree to collectively reduce this catastrophic pollution. A situation such as this, where the overuse of plastic could change - if it has not already done so - the morphology of the Earth. Since the 1950s, this material has grown so extensively that many researchers from all disciplines argue that it will remain as a geological marker of the Anthropocene.

Ne all use plastic film in our kitchens. Machinically. But since this film has existed, it has been produced in such quantities that there would be enough to wrap our entire planet. We all have a few plastic bottles of soda or mineral water in our homes. The UN has just published a discouraging figure: 5,000 billion plastic bags are consumed every year. Plastic is everywhere. So widespread that we don't even see it anymore. But what do you do with it once you use it? According to a study by PlasticsEuropeThe recycling rate of plastics in the EU28 (plus Norway and Switzerland) is 29.7 % and energy recovery (this corresponds to waste incineration with energy recovery) is 39.5 %. Only a small part of the plastic is therefore recycled. The rest, the trifle of 12 billion tonnes, is released into nature.

The oceans, plastic garbage can

The oceans have become a garbage can for the plastic we throw away. This material is so prevalent in the oceans that we talk about the "seventh continent". A recent report even states that, at the rate we are throwing away our plastics, there will soon be more plastic than fish in the world's seas.

Indeed, a study of the World Economic Forum and the Ellen McArthur Foundation notes that since the middle of the last century the use of plastics has increased twenty-fold and " is set to double again in the next 20 years... ». In the oceans, this rubbish is agglutinated by currents forming gigantic islands of waste, plastic continents.

Thus in the North Pacific, an area called "the Great Pacific Garbage Patch" is a veritable floating continent of plastic garbage. This area, discovered for the first time by the navigator Charles Moore, extends over 3.4 million km.² an area six times the size of France. There have been counted 300,000 pieces of plastic per km.². Another area of almost equal importance is in the North Atlantic. A major pollution which is turning into a real crime against the oceanic fauna. All regions are concerned, even those far from the coasts. This is the case of the Midway Islands, a small atoll in the Pacific far from the nearest continent by more than 2000 nautical miles. The population of albatrosses living there lose their lives by the tens of thousands, confusing the plastic waste with the food they catch for their offspring.

However, paradoxically, but even more worryingly, this plastic continent is gradually disappearing from our sight. This is far from good news, because if we can no longer see it, it has dissolved somewhere.

An important study scientist led by an international team of researchers went on the Malaspina expedition. Four ships were mobilized to survey five areas spread over several oceans, areas of intense marine currents (known as "gyres") where plastic accumulates. What did they discover? They found nothing.

99 % of the plastic has mysteriously disappeared. The mass of plastics dumped into the ocean is rated to 300 million tons. Researchers have counted only 40,000 tons.

The plastic entered the ocean food chain...

Several reasons are put forward to explain this phenomenon. Researchers explain that the most likely hypothesis to explain this differential would be that marine animals would have eaten the plastic! In the magazine ScienceScientists explain that when plastic floats on the surface of the oceans, waves and the sun's rays can break it down into smaller and smaller particles until they are so small that they begin to look like fish food. « Yeah, animals eat plastic. "says oceanographer Peter Davison of the Farallon Institute for Advanced Ecosystem Research in Petaluma, California. « All this is undeniable "he says.

However, it is very difficult to know the biological consequences of this phenomenon. When fish ingest the plastic, it is bound to end up in the food chain. Some of it is probably dissolved by toxins in the fish, but some of it is certainly going to end up on the shelves of our markets or in our cans of tuna or swordfish, for example. Carlos Duarte, an oceanographer at the University of Western Australia and co-author of this study, says in the magazine Verge that " plastic could enter the global ocean food chain ». It's the fish that would devour our garbage and he points out that we are part of the same food chain. He goes on to say... the consequences of this phenomenon on the ecosystem are still unknown ".

READ UP : Microplastics in the ocean: real trash continents

The invasion of plastic microbeads

If the fish eat some of the plastic we throw away, what about the rest? The decomposition of the plastic into finer and finer particles as the currents flow is a hypothesis to be retained. All the more so as these masses of decomposed particles are enriched by the release of plastic microbeads, which are increasingly present in a very large number of everyday consumer products. Plastic microbeads can be found everywhere, and especially in our cosmetic products - skin scrubs, shampoo, toothpaste, soaps.... Huffington Post cites figures from New York State alone, where 19 tonnes of microbeads are reportedly discharged into ducts every year. In the United Kingdom, between 16 and 86 tonnes of microplastic from facial scrubs would be discharged into the water every year.

According to a recent study published in the journal Environmental Science & Technologymore than 8 trillion microbeads enter aquatic habitats... every day. Their microscopic size prevents them from being filtered when they pass through a wastewater treatment plant. Once released into the sea, these microparticles have a very particular behavior: " They play a role in transporting contaminants, like a blotter. "explains François Galgani, a researcher at Ifremer, to HuffPost. He adds: " These plastic beads serve as a support for species, which can spread from one end of the planet to the other. ». These species can be microbes that, when they arrive in an unfamiliar environment, can unbalance the local flora and fauna and contaminate beaches and the seabed.

A study by Ifremer, published in the Comptes rendus de the American Academy of Sciences (PNAS), shows that these microbeads are ingested by all kinds of molluscs and severely disrupt their metabolism. The molluscs would produce fewer eggs and these would be smaller in size. Similarly, their spermatozoa would be much less mobile, all of which would seriously compromise the reproduction of many species, particularly oysters.

New plastic rock lines the ocean floor

When the plastic is not ingested by wildlife, or is not used as a surfboard with lots of microorganisms, it falls to the bottom of the ocean. This inert material, which is very difficult to degrade, becomes part of the sea floor in ever-increasing masses on the ground, on the seabed. A scientific study has even suggested that a new type of rock is emerging on the sea floor. This "rock", first introduced by researchers at the University of Ontario in GSA Todayis called "plastiglomerate".

According to this research, the degradation of plastic is a slow process that can occur mechanically, chemically (thermo- or photo-oxidation), and to a lesser degree, biologically. The persistence of plastic in the environment has been estimated to be in the order of hundreds of thousands of years, although this longevity may increase with climate. A recent study examining the accumulation of ocean debris in Monterey Bay, California, found that the accumulation of debris in the ocean is not as long as it would have been expected. s, at depths of 25 to 3971 metres over a 22-year period, shows that 33% of all this debris is plastic waste. Given water temperatures and reduced exposure to UV light at greater depths within and below the seal zone, plastic debris at this depth has good potential for persistence and, eventually, becomes part of the history of the rocks. Trapped in the sediment, the plastics mix with the substrate and create new, higher density fragments, called "plastiglomerates".

This term refers to a multi-composite material, hardened by agglutination of molten rock and plastics. This material is formed from combinations of basalt, corals, shells, and woody debris cemented together with grains of sand in a plastic matrix.

Researchers were able to identify all kinds of plastics used in the composition of these new rocks: fragments of ropes and fishing nets, remains of bottles and packaging, pipes, lids, etc. The researchers were also able to identify a number of other plastics used in the composition of these new rocks.

For researchers, this new material, which is likely to be found all over the planet, is a new geological marker, that of the Anthropocene. This expression, coined in 2000 by Nobel Prize winner Paul Crutzen, is used to identify the geological epoch in which we live; period that would have started with the industrial revolution, and would thus succeed the Holocene.

On a geological scale, our plastics are thus becoming the future fossils of our time.

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