Tara’s Journal – Microplastics: Luckless Oceans

© N. Pansiot / Tara Expéditions

Article from new Tara’s 10th journal

The oceans have become rubbish dumps. Some of the rubbish comes from maritime activities however eighty per cent of waste discharged into the sea comes from the land, transported by sewage systems, rivers, wind and storms. But worst of all, the vast majority of the floating detritus is plastic.

The Seventh Continent. That’s the name often given to this ocean of plastic pollution which floats on every sea, not only on the surface but also at depth. It’s an invisible environmental catastrophe in a faraway place, but very real and extremely noxious. Marine pollution by debris can be described thus: all solid material, whether manufactured or processed, that has been discarded or flushed into a marine or coastal environment.

 

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Cosmetics, Toothpaste, Washing Machines…

Each year between ten and twenty million tonnes of waste is discharged into the oceans and the fact is eighty per cent of it is plastic. Moreover, world production of plastic material has been increasing relentlessly over the last decades, amounting to 280 million tonnes in 2012. The volume absorbed by the sea is quite simply unimaginable. Today’s oceans are rubbish dumps. Through the combined action of the sun, oxidation and water currents some of this plastic waste degrades into very small pieces, microplastics, often less than five millimetres in size.

Eighty-eight per cent of the surface of the ocean is polluted with such tiny fragments…

Microplastics are synthetic polymers that are generally invisible to the naked eye. They comprise a wide range of particles that vary in size, shape, colour, density, chemical composition and source. In the form of tiny particles, known as primary microplastics, they can enter the marine environment in various ways, such as through our cosmetics, toothpastes, washing machines or industrial applications (pellets, balls, textile fibres, paint). Secondary microplastics, derived from the breakdown of larger plastic debris, are much greater in volume because the fragmentation process is, over time, infinite as more and more micro- and nanoparticles are released into the environment. It will take hundreds of years for them to disappear. Numerous expeditions have set out across the globe to collect samples and measure the concentration of these fragments. The results show that they are today omnipresent in the marine environment, at the surface and at depth, on the coast, in estuaries, in the open sea, in the most distant parts of the globe, from the equator to the poles. It is estimated that eighty-eight per cent of the surface of the ocean is polluted with such tiny fragments. As most microplastics are floating debris, they are borne along by currents and the wind, and accumulate on the surface of the sea. In addition, because of the rotation of the Earth, vortexes (or gyres as they are more commonly known) develop in the major oceans and concentrate these billions of plastic fragments into vast patches of pollution. Immense areas covered in plastic have been found, the most impressive being the “Great Garbage Patch” of the North Pacific which was discovered in 1997. In this zone, which is thirty metres deep and covers a surface area of 3.4 million square kilometres (roughly six times the size of France), there is ten times more plastic than plankton. This “plastic soup” is ingested by fish and even plankton, the very basis of our food chain.

 

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Toxic Substances

Unlike the Pacific, no permanent structures have been observed in the Mediterranean Sea. However the Med is one of the most polluted expanses of water in the world and the concentration of microplastics is on the same scale as that of the North Pacific. Nearly 250 billion plastic particles float on its surface, amounting to an estimated weight of 500 tonnes. Plastic debris are an acknowledged threat and are considered to be pollution, and their importance is only going to grow as the twenty-first century progresses. Plastics are chains of polymers made from both organic and inorganic materials, such as carbon, silicon, hydrogen, oxygen and derivatives of oil, coal and natural gas. Common plastic materials in use today are polystyrene (PS), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene terephthalate (PET), and these account for ninety per cent of production worldwide. These plastics all have particular properties. Some are inert while others contain substances added during the manufacturing process (plasticizers, fillers, colouring agents, fireproofing agents, stabilizers) which make the product more durable or improve its resistance to degradation and the effects of heat. The danger is that once they have entered the environment, these materials release chemicals such as phthalates and bisphenol A (BPA), substances greatly used as plasticizers. Worse still, plastics are veritable sponges when it comes to soaking up persistent organic pollutants (POPs). These POPs are complex molecules of anthropic origin—in other words, linked to human activity—such as pesticides, combustion products and industrial chemicals.

 

Interactions with Living Organisms

These noxious substances are very resistant to biodegradation, which means they remain in the environment for a long time before becoming harmless. Organisms on the surface of the microplastics absorb these contaminants, while additives contained in them—that is the plastics—are released into the marine environment. As a result they can accumulate in living tissue at every stage of the food chain (the process of biomagnification) and thus find their way into humans (bioaccumulation). Some of these additives are endocrine disruptors whose toxicological consequences on biodiversity, food safety and human health are only now coming to light. While macroplastic fragments floating in the sea directly affect marine birds and turtles (more than 100,000 marine animals die each year as a result of suffocating in plastic bags or mistaking waste for prey, and swallowing it), microplastics are a far more complex type of pollution, invisible and difficult to deal with. And because they are so small, they also absorb toxins and can then be ingested by all types of filter feeders, such as mussels and oysters. Clearly they can enter the food chain very easily.

Hydrophobic and non-biodegradable plastics are also colonized by microorganisms such as bacteria, algae and fungi. Carried thousands of kilometres by marine currents, these plastics act like rafts to spread invasive species and pathogens, thus wreaking havoc across the entire ecosystem.

Maria Luiza Pedrotti
Researcher at Villefranche-sur-Mer’s Oceanological Observatory (CNRS/UPMC)

 

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