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Plastic crusts colonize the rocks of the coastline

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Seen from a distance, it looks like huge pieces of gum stuck to the rocks. If we get a little closer, we understand that this strange material embedded in the rocks, literally becoming one with them, is plastic. When dumped into the oceans and beaten by the waves, the plastic bags and all the plastic garbage seem to turn into organic matter that, like algae and lichens, insinuates itself into the smallest interstices of the rocks. Plastic becomes mineral and transforms coastal landscapes and marine wildlife habitats.
 
On thought I had learned about the pollution and damage that plastic, in use around the world, does to the environment when it is thrown away without restraint. Unfortunately, we are now familiar with this "seventh continent", a giant garbage can floating on the ocean. Rubbish as far as the eye can see, which clumps together with the currents to form gigantic islands of rubbish, continents of plastic. We know that at the rate at which we throw plastic away, there will soon be more plastic than fish in the world's seas.
 
 
What we also know is that this plastic, when it floats on the surface of the oceans, is fragmented by the waves and the sun's rays into smaller and smaller particles that start to look like fish food. It is now a known fact that marine animals eat plastic. This material then inevitably ends up in the food chain. Some of it is probably dissolved by toxins in the fish, but some of it is sure to end up on the shelves of our markets or in our cans of tuna or swordfish.
 
It's also recently become known that if fish eat some of the plastic we throw away, the rest breaks down into finer and finer particles as we move with the currents. 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 and especially in our cosmetic products - skin scrubs, shampoo, toothpaste, soaps....
 
 

Birth of a mineral-plastic hybrid

What we didn't know is that all this plastic waste and these more or less fine particles, when they are beaten by the waves as they approach the coast, agglomerate with the rocks and form a crust of hybrid mineral and plastic material. This was discovered by a team from the Marine and Environmental Sciences Centre (MARE) in Portugal, which is monitoring the accumulation of plastics along the coast of the volcanic island of Madeira and assessing their subsequent impact on the local ecosystem. They come from published their work in the journal Science of the Total Environment. " The crusts probably originated when pieces of plastic were crushed against the rocky shoreline, resulting in the formation of plastic crusts on the rock in the same way that algae or lichens do. " Katie Bays, co-founder of the consulting firm Sandhill Strategy, said Ignacio Gestoso, marine ecologist. "Looks like it, he says, that someone left a piece of gum chewing on the rocks. The shape resembles that of natural organisms that embed themselves in rocks in the same way.
 
 
Chemical analysis revealed that the crust is indeed made of polyethylene, a material widely used in plastic bags and food packaging. According to the researchers, the polyethylene that clings to the shoreline now covers nearly 10 % of the rock surface. The team also found evidence that algae eating sea snails (Littorina littorea) were equally comfortable on the plastic crust as they were on the rock, suggesting that they could ingest plastic as well as algae. More research should tell us how widespread the problem is and what impact it could have on the surrounding wildlife, but for now, scientists just want to draw attention to the problem.
 

Anthropocene Markers

This discovery is similar to one made in 2014 by research teams at the University of Ontario who uncovered how man-made plastic manages to bond intimately with rock, resulting in a new material called plastiglomerates, rock-like substances made from molten plastic and organic debris.
 
According to these researchThe 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 plastics 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, at depths of 25 to 3971 metres over a 22-year period shows that 33% of all this debris is composed of plastic waste. Given water temperatures and decreased exposure to UV light at greater depths within and below the photic zone, plastic debris at this depth has a 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; an epoch that would have begun 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. And that's nothing to be happy about.
 
 

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