In 2010, 8 million tons of plastic garbage was thrown into the ocean（Jambeck et al. 2015）. This is the same as throwing enough plastic to fill a dump truck into the sea every other minute.
Plastic production is increasing explosively worldwide. It is estimated that the weight of plastic debris in the sea will exceed the weight of fish by 2050 if we continue to make plastic products and leak plastic waste into the sea at this pace（World Economic Forum 2016）.
Will all plastic waste that ends up in the sea disintegrate or disappear? Unfortunately, almost all plastics will not be broken down by living things（Andrady 1994）. Unlike naturally occurring organic materials, plastics, which are synthetic polymers, have a stable structure and are surprisingly strong, and they cannot be decomposed by living organisms.
Plastics have a high molecular weight, are hydrophobic, have a crosslinked structure, and are extremely strong. They decompose very slowly through thermal oxidation and photolysis, but in theory they will still exist for anywhere from hundreds of years to thousands of years（Barnes et al. 2009）. Therefore, unless it has been incinerated, plastic debris that was made around 1950 is still around somewhere today（Geyer et al. 2017）.
Once plastic enters the ocean, its lifespan will increase further. This is because thermal oxidative decomposition hardly occurs in the water, unlike on land, while photodegradation also barely takes place in the deep dark ocean（Andrady 2015）.
Therefore, it is believed that plastic waste produced today or in the past and abandoned in the ocean will remain there for decades, centuries, or even millennia. Some scientists go so far as to say that plastic fossils will form some day.
Will plastic waste that enters the ocean disintegrate or disappear? No, it will not. The decomposition referred to here means to be mineralized into water, carbon dioxide, methane, etc. Unfortunately, almost all plastics will not be disintegrated by living organisms. Also, plastic is still plastic even it has degraded and been miniaturized and is invisible to the naked eye.
Even biodegradable plastics that are “degraded by microorganisms” require special microorganisms and temperatures, so, unlike in land landfills or the composting process, plastics in the ocean will remain in the environment for a very long time（Kyrikou & Briassoulis 2007, UNPE 2015）.
Furthermore, most plastic products have additives added at the manufacturing stage. Additives are chemicals that are added to make plastics transparent, to soften them, or to add functions such as fire resistance and high durability. It is said that the lifetime of plastics containing such additives will be even longer.
Do bioplastics made from biological sources decompose in the ocean? Bioplastics are made from such raw materials as maize and algae. They are also made from renewable resources, thus have the advantage of not consuming fossil fuels.
Plastic waste that has entered the ocean cannot remain unscathed forever. Plastic debris is exposed to sunlight while drifting on the sea surface or while coming into contact with the coast. On the beach, the sand and waves create movement and pieces of plastic debris collide with each other and friction occurs. The plastic waste will be gradually weathered and miniaturized .
Even if a piece of plastic debris becomes small, its structure as a polymer remains intact and the plastic retains its nature（Hopewell et a. 2009）. Miniaturized plastics are called microplastics and these threaten the ecosystem.
Microplastics are found in the ocean all over the world（LITTERBASE）. They exist everywhere, from the shallows to the deep ocean. They are even found in the Arctic ice. It is impossible to remove them, and they will remain in the ocean environment for centuries to thousands of years.