Trajet des plastiques dans les Océans

Des plastiques dans l’océan

L’augmentation de la consommation des plastiques s’est accompagnée d’une pollution environnementale importante et croissante depuis les années 1950. Même si la gestion des déchets est une préoccupation actuelle, des millions de tonnes de déchets sont encore rejetés chaque année dans l’environnement. Acheminés principalement par les cours d’eau, les déchets plastiques finissent par arriver dans les océans.

trajet-des-plastiques-oceans

La grande majorité (80%) des plastiques observés dans les océans provient ainsi des continents, l’autre partie provient des activités en mer.
En fonction de leur densité, les déchets vont soit couler vers les fonds marins (comme les PVC de densité supérieure à celle de l’eau de mer), soit flotter et être entraînés par les courants marins (exemple du polyéthylène PE, de densité inférieure à celle de l’eau de mer).
Bouteilles*, sacs plastiques, fibres de textiles synthétiques (polyester, acrylique, polyamide, …), microbilles plastiques d’abrasifs industriels, d’exfoliants ou de produits cosmétiques, morceaux de polystyrène, pastilles de pré-production de plastiques, filets de pêche,… les déchets plastiques observables dans les eaux de surface océaniques sont d’origines diverses et de taille très variable, du microscopique au macroscopique.
* Sauf les bouteilles transparentes qui sont en PVC (eau, sodas): dès qu’elles sont cassées par l’érosion, le plastique plus dense que l’eau, coule…Par contre, on observe dans l’eau leurs bouchons, ainsi que les flacons et bouteilles non transparentes (lait, gel douche …)

Une dispersion mondiale des plastiques dans les océans

Les plastiques flottant en surface des océans sont entraînés des littoraux jusqu’à l’océan ouvert par les vents et courants marins. Les directions et les vitesses de déplacement dépendent de l’organisation générales des circulations atmosphériques et océaniques*.
A l’échelle du globe, les courants marins de surface, déviés par la rotation de la Terre, présentent une circulation « en tourbillon », en spirale, appelés gyres**.
On dénombre 5 gyres principaux : un dans l’océan Atlantique Nord, un dans l’océan Atlantique Sud, un dans l’océan indien, un dans l’océan Pacifique Nord et un dans le Pacifique sud :

Animation Vidéo ci-dessous

Gyres-1Gyres-2

Si les quantités globales de plastique dans les océans ne sont pas précisément estimées (en fonction des zones, on observe de 0 à 150 000 morceaux de plastiques au km2 sur les fonds marins et de 0 à 900 000 microplastiques dans les eaux de surface …), les études montrent que
leur dispersion suivant les grands courants marins se fait rapidement*** et à l’échelle mondiale.
* Les circulations atmosphériques et océaniques sont liées et ont pour «moteur » l’énergie solaire. En effet, les différences d’énergie solaire reçue par la surface terrestre selon les zones (plus d’énergie reçue à l’équateur qu’aux pôles en raison de la sphéricité de la terre) et la rotation de la Terre autour de son axe (force de Coriolis) entraînent l’existence de grandes cellules de convection atmosphériques (cellules « de Hadley » à l’équateur, « de Ferrel » dans les zones tempérée et cellules polaires aux pôles).
Les mouvements d’air horizontaux de ces mouvements atmosphériques sont les vents. Ces vents entraînent des mouvements d’eau, de la surface jusqu’à plus de 100 m en profondeur. Les déplacements des déchets plastiques dépendent des sens et vitesses des vents et courants marins de surface.
** les gyres montrent un mouvement en spirale avec enroulement sur la droite dans l’hémisphère droit et sur la gauche dans l’hémisphère sud, en relation avec la force de Coriolis (rotation de la Terre).
*** Les suivis de bouées dérivantes et les modèles océaniques établis à partir des observations satellites montrent que les plastiques parcourent souvent plusieurs kilomètres par jour.

Des zones d’accumulation de plastiques : les « continents plastiques »

Les courants marins d’échelle planétaire transportent les déchets vers les zones centrales des gyres, très calmes. Les plastiques s’y concentrent et s’accumulent ainsi sur d’immenses surfaces (Exemple du « Great Pacific Garbage Patch » dans l’océan Pacifique Nord, de surface estimée à six fois celle de la France).
Les « continents plastiques », existent ainsi dans les cinq grands bassins océaniques.
Illustration : Carte des concentrations moyennes de déchets plastiques mesurées dans les eaux de surface de 442 sites. (Zones grises : zones d’accumulation prévues par un modèle de circulation de la surface océanique)

Gyres-3

Le terme « continent » est une métaphore : les surfaces concernées sont de l’ordre des continents, mais il ne s’agit pas d’étendues « solides » :
la pollution plastique de l’océan est plutôt une « soupe plastique», autre
terme également utilisé.

Soupe-plastique

Droits Photo: Charles Moore, Sur : Coastalecare.org

S’il existe des macrodéchets, les 7ièmes continents sont surtout constitués de petits éléments plastiques, souvent invisibles sans une fine observation, issus en grande partie de la dégradation des plastiques.
Plus ou moins longue en fonction des matériaux et de leur épaisseur, la durée de dégradation est estimée en laboratoire de 1 à 5 ans pour le fil de nylon, de 1 à 20 ans pour les emballages
plastiques fins, jusqu’à 450 ans pour les bouteilles plastiques et encore plus pour d’autres matériaux.
La dégradation dépend également de l’action de certains facteurs environnementaux:
– sous l’action mécanique*, le plastique se fragmente (mais les fragments restent des polymères plastiques stables et durables)
– sous l’action chimique ** ou enzymatique de dépolymérisation, les polymères plastiques sont décomposés et détruits.
Flottant à la surface des océans, les matériaux plastiques sont essentiellement soumis à l’érosion et à l’action du rayonnement solaire et se fragmentent progressivement en morceaux de plus en plus petits. La concentration en micro particules de plastique invisibles à l’oeil nu
aurait ainsi triplé dans les eaux de surface depuis les années 70.

*action d’érosion par les vagues
** action chimique des UV du soleil : réactions photochimiques. (Pour le PE on observe principalement des réactions radicalaires, notamment d’oxydation)

Microplastiques

Microplastiques (Malaspina 2010 expedition.) Credit: ©CSIC

Des zones de disparition de plastiques ?

Des analyses récentes sembleraient indiquer une « disparition » de déchets plastiques dans les eaux de surface océanique : en effet, les quantités de plastiques arrivées dans les océans depuis les années 50 auraient dû entraîner des concentrations supérieures à celles mesurées. Les eaux de surface ne semblent pas être la destination finale des déchets plastiques flottants dans l’océan…
Plusieurs mécanismes possibles pour expliquer l’élimination des  plastiques de la surface océanique sont proposés :
– la formation de biofilms et la colonisation par des organismes pourraient diminuer la flottabilité et permettre à certains débris de plastique de couler dans les eaux profondes, et de se déposer sur le fond marin.
Cependant les observations montrent que les particules plastiques sont de faible densité dans les sédiments et n’enregistrent pas une augmentation de la concentration en plastiques en fonction du temps pour un même lieu.
– la fragmentation et photodégradation des matières plastiques seraient rapides et ne permettraient plus leur observation. Les fragments seraient assez petits pour passer à travers les filets d’échantillonnage standard, avec une taille de l’ordre du micron ou plus petite.
– un transfert de matières plastiques de l’eau vers les organismes : l’assimilation des microplastiques par ingestion et entrée dans les réseaux trophiques engendrerait un « stockage » de la matière dans les organismes et diminuerait la concentration de plastiques dans l’eau. On observe en effet la présence de plastique dans l’estomac de nombreuses espèces marines, même jusqu’à chez 39% des poissons mésopélagiques*.
De plus, la taille des fragments de plastique ingérés par ces poissons, comprise entre 0,5 et 5 mm, correspond à la taille des débris de plastique « disparus » dans les évaluations mondiales des plastiques en surface océanique.
– l’intervention d’autres processus encore à découvrir …

*Les poissons mésopélagiques jouent un rôle important dans l’écosystème marin; ils sont omniprésents et très abondants dans l’océan ouvert. Ils vivent dans la couche intermédiaire de l’océan (200 à 1.000 m de profondeur), mais migrent pour s’alimenter vers la couche de surface
la nuit.

Source : Nathalie Briand – MobiScience.briand.free.fr

An Ocean of Plastic

The world’s waste has formed a vast floating garbage dump that’s twice the size of Texas, and it’s working its way up the food chain

– BY |

Welcome to the future,” says Capt. Charles Moore, the commander of a 25-ton research vessel called Alguita. He’s standing in Kewalo Basin Harbor on the south shore of Oahu, holding up a jug filled with murky yellow liquid. Tiny bits of debris swirl in the jug, a cloudy mass of trash. Most of it is plastic.

“This is what our oceans look like now,” Moore continues in a mariner’s drawl. “This sam­ple was taken in the Pacific about 1,000 miles west-southwest of Los Angeles. But I need to emphasize that this is not just one place—this is the whole ocean.” The liquid in the jug resembles a gut­ter puddle in Manhattan more than the placid blue of the Pacific.

It was Moore who, in 1997, made a dis­covery about the ocean that raised alarms around the world. Returning home to California after a sailing race to Hawaii, he plotted a course through the North Pacific Gyre, an area known to sailors as the “doldrums.” Encompassing some 10 million square miles, the gyre is home to trade winds and circular currents that tend to keep whatever mean­ders into it without self-propul­sion for months, years, even dec­ades at a time. There, near the center of the slow, deep, clock­wise currents that form this oce­anic eddy, Moore came across a vast mass of floating debris that has become known as the Great Pacific Garbage Patch.

The first thing you need to know about the Great Pacific Garbage Patch is that its name, which conjures up images of an an­imated Charlie Brown special, is disgust­ingly inappropriate. In reality, the “patch” is a swirling vortex of plastic soup, an im­mense, fetid swamp of debris where tiny bits of decaying plastic outweigh surface zooplankton—one of the most prolific and abundant organisms on the planet—by a ratio of six-to-one. Nobotly knows its exact size or if it has any boundaries at all: Its location and shape vary depending on factors such as water temperature, season and major weather events like El Niño. Scientists estimate it is twice the size of Texas—maybe even larger—and contains some 10 million tons of waste.

“At first you see blue water stretching to the horizon,” says Mary Crowley, direc­tor of the Ocean Voyages Institute. “That makes it seem like everything is quite all right. But then, when you really look into the water, you see this never-ending plas- tic confetti. We usually gather individual pieces of plastic at a rate of 200 to 300 every 30 minutes—and that’s just in our im­mediate vicinity.” Since the study started, researchers have not found a single sample in the gyre devoid of plastic.

Because most of the debris consists of “microplastics”—larger chunks of waste that have been re­duced to tiny bits of polymer by the com­bined effect of waves, wind and sun—it poses an especially dire threat to wildlife. Particulated plastic is more likely to be eaten by birds and fish—and can contain concentrations of toxic chemicals, includ­ing DDT and PCBs, as much as a million times greater than the surrounding seawater. On Midway Atoll, albatross chicks are dying from starvation, their bellies full of plastic. Sea turtles mistake buoyant plastic bags for jellyfish, one of their main sources of prey, and choke to death. In a recent sample of 670 myctophids, a major source of food for larger fish, the crew of Alguita found 1,298 pieces of plastic. “It’s becoming the new diet,” says Moore. “We’re putting everything in the ocean on a plastic diet.”

It’s hard to believe plastic has only been around for a century. In 1909, a Belgian-born chemist named Leo Hendrik Baekeland introduced the first completely synthetic plastic, a phenol-formaldehyde compound he called Bakelite, to the world at a conference of chemists in New York. Bakelite, first synthesized in Baekeland’s barn in Yonkers, New York, was made by mixing carbolic acid and formaldehyde. It had the near-mystical property of being malleable when heated under pressure, while becoming rigid and insoluble when cooled. Highly moldable, more durable than ceramics, lighter than metal and made entirely in the lab, the new compos­ite was also electrically nonconductive and heat-resistant, quickly earning it the title “material of a thousand uses.”

First it was nylon, which hit the market in 1940, later causing riots at department stores as women stampeded over one an­other for a pair of stockings. Mass production of other plastics came after World War II with the advent of polyethylene, polypropylene and polystyrene, which serve as key ingredients in products like Saran Wrap, disposable milk jugs, Hula-Hoops and Styrofoam. By the 1960s, plas­tics were a ubiquitous part of American life and the very picture of modernity. By 1979, the annual volume of plastic pro­duced in the U.S. overtook that of steel.

Lauded as the “miracle” behind modern life, today plastic is everywhere. It’s in our clothes, computers, cellphones, cars, fur­niture and refrigerators. Airplanes, hos­pitals and laboratories depend upon it, but mostly, it ends up in our trash cans. Next year, the world will pump out close to 300 million tons of plastic, well more than a third of it falling into the catego­ry of “minimal use,” meaning it will be discarded anytime within a few seconds to one year. In the United States, 25 bil­lion pounds of plastic go unaccounted for each year. Where does it go? Where does a relatively indestructible material go in a finite world? “Except for a small amount that’s been incinerated, every bit of plastic we’ve put in the oceans still remains,” says Anthony Andrady, a lead­ing research scientist who specializes in plastics. “It’s still somewhere in the ma­rine environment.”

When was the last time you spent an entire day without using a piece of dis­posable plastic? It surrounds us, inun­dates us. It gathers in the gutters of cities, washes up on every coastline in the world and floats in the oceans themselves. The United Nations Environment Program es­timates that plastic debris kills more than 100,000 marine mammals and 1 million seabirds every year. Even small organisms like jellyfish, lanternfish and zooplankton have started to ingest tiny bits of plastic. These species, the very foundation of the oceanic food web, are becoming saturated with plastic, which may be passed farther up the food chain. “The concern is what the plastic is carrying and releasing into organisms that ingest it,” says Holly Bamford, who is launching a study of marine debris for the National Oceanic and At­mospheric Administration. The bottom line is: It’s all our own shit, and we’re quite literally starting to eat it.

Even though plastic disintegrates over time, leaching chemicals like bisphenol-A and phthalates into the environment, most of it never disappears; the synthetic polymers that form its building blocks remain intact. In its tiniest, most par-ticulated state, Andrady explains, “plas­tic is still plastic. The material still re­mains a polymer. Polyethylene—the most pervasive type of disposable plastic—is not biodegraded in any practical time scale. There is no mechanism in the ma­rine environment to biodegrade that long a molecule.”

When fish and mammals ingest microplastics from the Great Pacific Garbage Patch, the chemical toxins concentrated in the waste lodge themselves in the animals’ fatty tissues, accumulating at ever-increasing levels the higher you go up the food chain. It isn’t clear yet if these chem­icals are reaching humans, but PCBs and DDT are known to disrupt reproduction in marine mammals. In humans they have been linked to liver damage, skin lesions and cancer. “The possibility of more and more creatures ingesting plas­tics that contain concentrated pollutants is real and quite disturbing,” says Richard Thompson, a British marine biolo­gist who has been studying microplastics for 20 years.

Wayne Sentman, a field biologist with the San Francisco-based Oceanic Soci­ety, has spent three years on Midway Atoll conducting field research on dead albatrosses. During that time, he has found a wide array of marine debris inside the bel­lies of dead birds, including “six lighters in one chick, a complete syringe with the needle, a small flashlight, various small light bulbs, combs, toothbrushes, parts of flip-flops and fishing tackle.” On British coastlines in the North Sea, a study of ful­mars found that 95 percent of the seabirds had plastic in their stomachs, with an av­erage of 44 pieces per bird. A proportion­al amount in a human being would weigh nearly five pounds.

The data about plastic debris in the oceans is still in its nascent stages, and scien­tists with the National Oce­anic and Atmospheric Ad­ministration stress that more research is needed to determine whether plastic has become a toxin in the food chain. But the evidence is mounting, and the amount of debris continues to double each decade. The threat extends well beyond the Great Pacific Garbage Patch: As Capt. Moore is quick to point out, the North Pacific Gyre is only one of five major gyres in the world’s oceans. “Half of the world’s oceans are accumulators—these high-pressure gyres that bring stuff into themselves,” he says. “And every single one of them is full of plastic.”

The question now is what, if anything, can we do about it? Some researchers are exploring ways to clean up the plastic by using an emerging technology to con­vert the oceans of plastic waste into fuel. One of the principal ingredients of plastic, after all, is crude oil—four percent of the world’s entire supply, to be exact, or about 3.4 million barrels of oil a day at our cur­rent levels of consumption. If the energy in plastic could somehow be released, the thinking goes, it could simultaneously solve the waste problem while easing en­ergy demand.

“Plastic is made from crude,” says Alka Zadgaonkar, head of the department of applied chemistry at the G.H. Raisoni College of Engineering in Nagpur, India. “If you break it down, what you get is liq­uid hydrocarbon.” With a loan from the State Bank of India, Zadgaonkar says she has developed a system that, with the aid of a secret catalyst, can turn “one kilo­gram of waste plastic into one liter of hydrocarbon.” The hydrocarbons can then be distilled into a rough gasoline suitable for powering machinery, motorcycles and heating systems.

The problem is that extracting a single liter of fuel takes one kilogram of plas­tic and 100 grams of coal, which doesn’t exactly make the process ecofriendly. What’s more, there is currently no prac­tical method to capture the liquid grave­yard of waste floating in the Pacific. “The biggest task we now face is how to catch it,” says Doug Woodring, the co-founder of a study of the Great Pacific Garbage Patch called Project Kaisei. “That is where the technology is uncertain.”

The only viable way to stop the spread of plastic into the world’s food chain, say those studying the danger, is to reduce the amount of plastic we use. “There’s no way you can clean all this shit up—it’s impos­sible,” says Capt. Moore. “Right now we’re catching all this stuff with a small net. What are you going to do—drag these nets through the entire ocean?”

Moore, who stumbled across the Great Pacific Garbage Patch by accident, looks more like a sailor than a scientist, and his language is as salty as his thick head of curly hair. Unlike other researchers, used to the measured talk of scientific conferences, Moore cuts to the heart of the matter. “All this bullshit about going out there and scooping this stuff up—you can’t scoop this stuff up!” he says. “No way in hell you’re going to get that out of there—it’s just not feasible! The idea that there’s this ‘convergence zone’ in the gyre, and the plastic waste all goes there—well, if it’s all going there, it’s coming from other places and screwing up those parts of the ocean too. If the input is constant, then that just makes the whole ocean fucked up.”

Moore pauses, looking out over the Pa­cific. “No matter where you are, there’s no getting over it, no getting away from it,” he says. “It’s a plastic ocean now.”

Source : RollingStone

Green Concrete using Plastic Waste

International Journal of Engineering Trends and Technology (IJETT) – Volume 19 Number 4 – Jan 2015

IV. CONCLUSION

Based on the results of the experimental investigation, following conclusions could be drawn as follows: In Concrete, Natural sand can be replaced with plastic waste by 10 to 20% to achieve green concrete. Sand can also be replaced up to 30% in the members of building which do not carry high load. Using plastic waste such as polyvinyl chloride (PVC), Polypropylene (PP), Polyethylene in concrete reduces the environmental issues and minimizes the difficulties of dumping the major plastic waste. This will help to tackle the increasing pollution all over the world, especially in countries that face the complications regarding waste. In addition to the environmental benefits, it was noted that using plastic scrap can be used to fight against the obstacle of scarcity of natural sand in India. Also it was perceived that using aluminum powder in concrete containing plastic waste will minimize the dead load of concrete which is of crucial importance. Ultimately the use of such plastic waste material cuts down the cost of construction and also the aftermath of using plastic scrap in concrete will be magnificent.

Source : International Journal of Engineering Trends and Technology (IJETT) – Volume 19 Number 4 – Jan 2015

Why Sand Is Disappearing ?

BERKELEY, Calif. — TO those of us who visit beaches only in summer, they seem as permanent a part of our natural heritage as the Rocky Mountains and the Great Lakes. But shore dwellers know differently. Beaches are the most transitory of landscapes, and sand beaches the most vulnerable of all. During big storms, especially in winter, they can simply vanish, only to magically reappear in time for the summer season.

It could once be said that “a beach is a place where sand stops to rest for a moment before resuming its journey to somewhere else,” as the naturalist D. W. Bennett wrote in the book “Living With the New Jersey Shore.” Sand moved along the shore and from beach to sea bottom and back again, forming shorelines and barrier islands that until recently were able to repair themselves on a regular basis, producing the illusion of permanence.

Today, however, 75 to 90 percent of the world’s natural sand beaches are disappearing, due partly to rising sea levels and increased storm action, but also to massive erosion caused by the human development of shores. Many low-lying barrier islands are already submerged.

Yet the extent of this global crisis is obscured because so-called beach nourishment projects attempt to hold sand in place and repair the damage by the time summer people return, creating the illusion of an eternal shore.

Before next summer, endless lines of dump trucks will have filled in bare spots and restored dunes. Virginia Beach alone has been restored more than 50 times. In recent decades, East Coast barrier islands have used 23 million loads of sand, much of it mined inland and the rest dredged from coastal waters — a practice that disturbs the sea bottom, creating turbidity that kills coral beds and damages spawning grounds, which hurts inshore fisheries.

The sand and gravel business is now growing faster than the economy as a whole. In the United States, the market for mined sand has become a billion-dollar annual business, growing at 10 percent a year since 2008. Interior mining operations use huge machines working in open pits to dig down under the earth’s surface to get sand left behind by ancient glaciers. But as demand has risen — and the damming of rivers has held back the flow of sand from mountainous interiors — natural sources of sand have been shrinking.

One might think that desert sand would be a ready substitute, but its grains are finer and smoother; they don’t adhere to rougher sand grains, and tend to blow away. As a result, the desert state of Dubai brings sand for its beaches all the way from Australia.

And now there is a global beach-quality sand shortage, caused by the industries that have come to rely on it. Sand is vital to the manufacturing of abrasives, glass, plastics, microchips and even toothpaste, and, most recently, to the process of hydraulic fracturing. The quality of silicate sand found in the northern Midwest has produced what is being called a “sand rush” there, more than doubling regional sand pit mining since 2009.

But the greatest industrial consumer of all is the concrete industry. Sand from Port Washington on Long Island — 140 million cubic yards of it — built the tunnels and sidewalks of Manhattan from the 1880s onward. Concrete still takes 80 percent of all that mining can deliver. Apart from water and air, sand is the natural element most in demand around the world, a situation that puts the preservation of beaches and their flora and fauna in great danger. Today, a branch of Cemex, one of the world’s largest cement suppliers, is still busy on the shores of Monterey Bay in California, where its operations endanger several protected species.

The huge sand mining operations emerging worldwide, many of them illegal, are happening out of sight and out of mind, as far as the developed world is concerned. But in India, where the government has stepped in to limit sand mining along its shores, illegal mining operations by what is now referred to as the “sand mafia” defy these regulations. In Sierra Leone, poor villagers are encouraged to sell off their sand to illegal operations, ruining their own shores for fishing. Some Indonesian sand islands have been devastated by sand mining.

It is time for us to understand where sand comes from and where it is going. Sand was once locked up in mountains and it took eons of erosion before it was released into rivers and made its way to the sea. As Rachel Carson wrote in 1958, “in every curving beach, in every grain of sand, there is a story of the earth.” Now those grains are sequestered yet again — often in the very concrete sea walls that contribute to beach erosion.

We need to stop taking sand for granted and think of it as an endangered natural resource. Glass and concrete can be recycled back into sand, but there will never be enough to meet the demand of every resort. So we need better conservation plans for shore and coastal areas. Beach replenishment — the mining and trucking and dredging of sand to meet tourist expectations — must be evaluated on a case-by-case basis, with environmental considerations taking top priority. Only this will ensure that the story of the earth will still have subsequent chapters told in grains of sand.

NOV. 4, 2014

Sargassum on Trinidad & Tobago’s Coastlines

[:en]Mounds of sargassum seaweed have carpeted the shoreline for miles. Fishermen continue to battle with the seaweed just to make an honest living, and it doesn’t seem to be getting any better.
[:fr]Mounds of sargassum seaweed have carpeted the shoreline for miles. Fishermen continue to battle with the seaweed just to make an honest living, and it doesn’t seem to be getting any better.
[youtube https://www.youtube.com/watch?v=9xRv8rv1fb0?rel=0&showinfo=0][:]