Microplastics

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Microplastics are fragments of any type of plastic less than 5 mm (0.20 in) in length,^[1] according to the U.S. National Oceanic and Atmospheric Administration (NOAA)^[2][3] and the European Chemicals Agency.^[4] US EPA researchers define microplastics, or MPs, as plastic particles ranging in size from 5 millimeters (mm), which is about the size of a pencil eraser, to 1 nanometer (nm). For comparison, a strand of human hair is about 80,000 nanometers wide.^[5]

They cause pollution by entering natural ecosystems from a variety of sources, including cosmetics, clothing, construction, renovation, food packaging, and industrial processes.^[1][6] The term microplastics is used to differentiate from larger, non-microscopic plastic waste. Two classifications of microplastics are currently recognized. Primary microplastics include any plastic fragments or particles that are already 5.0 mm in size or less before entering the environment.^[6] These include microfibers from clothing, microbeads, plastic glitter^[7] and plastic pellets (also known as nurdles).^[8][9][10] Secondary microplastics arise from the degradation (breakdown) of larger plastic products through natural weathering processes after entering the environment.^[6] Such sources of secondary microplastics include water and soda bottles, fishing nets, plastic bags, microwave containers, tea bags and tire wear.^{[11][10][12][13]}

Both types are recognized to persist in the environment at high levels, particularly in aquatic and marine ecosystems, where they cause water pollution.^[14] 35% of all ocean microplastics come from textiles/clothing, primarily due to the erosion of polyester, acrylic, or nylon-based clothing, often during the washing process.^[15] Microplastics also accumulate in the air and terrestrial ecosystems. Airborne microplastics have been detected in the atmosphere, as well as indoors and outdoors. Because plastics degrade slowly (often over hundreds to thousands of years),^[16][17] microplastics have a high probability of ingestion, incorporation into, and accumulation in the bodies and tissues of many organisms.^[1] The toxic chemicals that come from both the ocean and runoff can also biomagnify up the food chain.^[18][19] In terrestrial ecosystems, microplastics have been demonstrated to reduce the viability of soil ecosystems.^[20][21] As of 2023, the cycle and movement of microplastics in the environment was not fully known.^[6] Microplastics in surface sample ocean surveys might have been underestimated as deep layer ocean sediment surveys in China found that plastics are present in deposition layers far older than the invention of plastics.

Microplastics are likely to degrade into smaller nanoplastics through chemical weathering processes, mechanical breakdown, and even through the digestive processes of animals. Nanoplastics, or NPs, are a subset of microplastics and they are smaller than 1 µm (1 micrometer or 1000 nm). Nanoplastics cannot be seen by the human eye.^[5]