||Mukesh Doble, Ramasamy Venkatesan
||Smithers Rapra Technology
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Plastics are synthetic organic polymers that are produced worldwide at a rate of 100 million tons per year and have replaced several construction, automobile and engineering materials, because of their advantages, ease of fabrication, and cost. Plastics and composites which include polyester, polyethylenes, fluorinated hydrocarbons, foams, urethanes, carbon fibre reinforced plastic and glass fibre reinforced plastic and so on, are also used in marine applications as hulls, fenders, insulating materials, pipelines and so on. The increased consumption over time has led to escalating levels of them as waste in the land and in the ocean. The waste from the land reaches marine waters via industrial discharge, littering beaches and runoff. Most polymers are highly persistent in the marine environment and those that float degrade slowly via photocatalysis using ultraviolet (UV) radiation. Plastics that sink remain persistent for very long periods of time. Approximately 80% of plastic pollution in the sea originates from the land, and the rest is produced from recreational sailors, commercial operations, maritime industries, and the military. Plastics that reach the sea break down into microplastics (less than 5 mm) because of the activity of nature. A gyre is a naturally occurring vortex of wind and ocean current that rotates in a clockwise direction in the northern hemisphere and counterclockwise in the southern hemisphere seas. Currently there are five gyres. The North Pacific Gyre, also known as the Great Pacific Garbage Patch, swirls in the Pacific Ocean between the coast of California and Hawaii and contains about 11 million tons of floating plastic covering an area of nearly 5 million square miles in the Pacific Ocean. Sea animals including turtles, seabirds, sea lions, seals, mammals and fish get entangled or ingest these marine debris and die. Debris that settles on the seabed inhibits the exchange of gases between the pores in the sediments and the overlaying water which affects the oxygen supply to the ocean floor. This, in turn interferes with the organisms that are present on the sea floor and finally affect the ecosystem. Chemicals leach out from the plastics which could be toxic and are then absorbed by the animals and fish. For example bisphenol A, one of the monomers of polycarbonate, a transparent engineering plastic, is an endocrine disordering chemical which leaches out when thrown in the dump yards or in water bodies and can affect fish and other marine creatures.