Other meanings of Microplastics
Environmental science
Microplastics are small plastic particles resulting from manufactured products or the breakdown of larger plastics. They are commonly defined as particles smaller than 5 millimetres, although researchers increasingly distinguish still-smaller nanoplastics. Their persistence, mobility, and tendency to carry chemical additives or pollutants have made them a major subject in marine science, freshwater research, and public-health assessment.
Microplastics are defined chiefly by particle size, not by a single chemical composition. The widely used threshold is less than 5 millimetres, and particles may be fragments, fibres, films, foams, or beads made from polymers such as polyethylene, polypropylene, polystyrene, and polyvinyl chloride. Primary microplastics are manufactured at small sizes, including industrial pellets, cosmetic particles, and some abrasive media. Secondary microplastics form when sunlight, oxygen, heat, and mechanical wear fragment larger objects such as packaging, fishing gear, paint, and synthetic textiles.1
The boundary is practical rather than a claim that particles above 5 millimetres are harmless. Larger debris can continue breaking down, while the smallest particles—often called nanoplastics—are difficult to detect and do not yet have a universally applied measurement standard.
Microplastics move between land, freshwater, oceans, sediments, and the atmosphere rather than remaining at their point of release. Urban runoff, wastewater effluent, sewage sludge, litter degradation, tire wear, and textile laundering are important pathways; wind can transport fibres and fragments through the air, and rainfall can return them to land or water.1 Wastewater treatment can remove many particles from the water stream, but captured material may be concentrated in sludge and later redistributed if that sludge is applied to soil.
Particle behaviour depends on density, shape, surface chemistry, and biofouling. Some plastics float, whereas denser polymers or particles attached to organic matter sink. Currents, estuaries, sea ice, and sediment can therefore act as temporary reservoirs. Microplastics have been found in remote environments, including polar regions, demonstrating that distance from cities does not prevent exposure.4
Microplastics can be ingested by organisms across food webs, from plankton and benthic invertebrates to fish, seabirds, and marine mammals. Laboratory and field studies have examined physical blockage, reduced feeding, inflammation, altered energy budgets, and the transport of attached chemicals or microorganisms, but effects vary greatly with particle size, dose, polymer, and exposure duration.3
People may encounter particles through food, drinking water, household dust, and inhalation. The World Health Organization concluded that available evidence did not establish a clear human-health risk from microplastics in drinking water, while emphasizing substantial uncertainties in measurement, exposure, and toxicology.2 Potential concerns include additives, persistent pollutants, and biological responses, but detection alone does not demonstrate disease. Research therefore distinguishes hazard—the capacity to cause harm—from risk under realistic exposure conditions.
The most informative measurements often concern particle shape and material, not just total count. Fibres from clothing and ropes, irregular weathered fragments, thin films, and tire-derived particles behave differently and may require different sampling and analytical methods. Contamination from laboratory clothing, air, and equipment can also distort results, so clean procedures and chemical confirmation are essential.
Microplastics are not exclusively an ocean problem: agricultural soils can receive particles in compost, irrigation water, atmospheric deposition, and sewage-derived amendments. Paint abrasion from buildings, roads, and ships is another overlooked source. Conversely, some particles are intentionally used in industrial processes and can be controlled at the source more readily than diffuse pollution. The most effective responses combine product redesign, improved waste collection, restrictions on preventable releases, textile and tire controls, and standardized monitoring rather than relying on cleanup alone.4
Particle counts are not directly comparable when studies use different size cutoffs, sampling locations, contamination controls, or analytical methods.
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