Plastic waste can travel thousands of kilometers across oceans without degrading due to their molecular structure being resistant to natural decomposition processes, such as the action of microbes or environmental conditions.
Plastics are polymers, large chains of molecules that are very chemically stable, which means they last a long time. Especially since most of them, like polyethylene and polypropylene, are extremely resistant because they hardly react with water or salt. Their chemical structures are stable, and almost no bacteria or marine organisms can easily attack them to break them down. Additionally, the additives often added to plastics, such as certain UV stabilizers or antioxidants, further increase their resistance to harsh conditions in the oceans. As a result, a plastic bottle or bag can float calmly for years with almost no changes.
In the oceans, it is rather cold, and the low temperature slows down the degradation of plastic. For a material to decompose, a little warmth always helps, just like when you keep your food in the fridge to keep it fresh and prevent it from spoiling. Additionally, in oceanic conditions, there is often little available oxygen, especially in the depths, so the chemical reactions responsible for degradation occur slowly or not at all. Finally, the low light limits the effect of UV: less sunlight means less photochemical reaction to break down those stubborn plastics. In short, under these conditions, plastic can float peacefully for years without degrading.
Ocean currents act like real conveyor belts, transporting plastic waste far away from its place of origin. The ocean gyre, a massive loop of marine currents, concentrates plastics into real floating "islands" that can stretch for thousands of kilometers. Waste can sometimes be carried for years in this ocean circuit. Lightweight plastics, easily floating on the surface of the water, can travel great distances thanks to these currents. A plastic bag discarded on a European beach may end up a few years later near the coasts of America or Africa. Large quantities of plastic accumulate in remote areas off the coasts, forming concentrations known as the infamous Great Pacific Garbage Patch.
UV rays make plastics brittle by gradually destroying their molecules. This process is called photodegradation and weakens the plastic without completely making it disappear. Saltwater, on the other hand, acts differently: it further slows down this degradation by stabilizing certain chemical structures in plastics. As a result, even if they become small pieces, they remain there for decades. Just because they become invisible to the naked eye doesn’t mean they disappear; they simply become even more resilient microplastics.
Typical marine organisms, which love to nibble on wood or algae, find no nutritional interest in plastic. Most plastics are made from artificial polymers whose chemical bonds are extremely strong, making them difficult to break down for these organisms. As a result, bacteria and other small marine creatures that are usually capable of decomposing natural materials simply do not know what to do with these strange materials. This makes plastic biologically resistant, therefore nearly unwearable, sometimes floating for several years before even being slightly altered. The almost complete lack of specialized marine organisms capable of digesting plastic further slows its potential degradation, allowing this waste to travel quietly from one continent to another.
Some plastic waste found on beaches comes from regions located thousands of kilometers away, transported by major ocean currents known as gyres.
The 'plastic continent' located in the North Pacific covers an estimated area about three times the size of France, demonstrating how plastic waste can be transported over very long distances.
Nearly 80% of the plastic waste found in the ocean comes from land-based activities, such as littering objects or bottles on beaches or throwing waste into waterways.
It is estimated that certain plastics can take between 400 and 1,000 years to completely decompose in the oceans, due to their resistant chemical properties and specific environmental conditions.
Ocean currents, such as gyres, act like true highways, passively transporting floating plastic debris over hundreds or even thousands of kilometers, allowing them to disperse on a global scale.
Very few marine organisms can effectively break down plastic. The majority of them do not have the necessary enzymes to degrade the complex polymers that make up plastics, which contributes to their accumulation in the marine environment.
The long lifespan of plastics in the ocean leads to numerous ecological impacts: ingestion by marine wildlife, entanglement of animals in debris, introduction of toxic chemicals along the food chain, and alteration of marine ecosystems.
To reduce the global transport of plastic waste, it is essential to prevent its entry into the marine environment through efficient recycling, reducing plastic packaging, and developing technologies for intercepting and eliminating ocean waste before it spreads.
Plastics are materials that are very resistant to natural degradation. Their chemical stability makes them very unreactive to environmental influences such as salt, UV rays, and marine microorganisms, which explains their persistence over long periods.
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