Microplastics

Microplastics are small plastic particles or fibres, commonly defined as less than five millimetres in size. The term covers different shapes, including fragments, fibres, films, foams, pellets and beads; standardized sampling and laboratory methods are important for comparing measurements, and protocols continue to be developed and tested. Primary microplastics are manufactured at small sizes or as pellets used to make larger plastic products. Secondary microplastics form when larger plastic items break down or shed particles during use.

Sources include plastic resin pellets lost during production or transport; microbeads intentionally added to some products; fragments of discarded bags, bottles and other items; and particles released through the wear of vehicle tyres, synthetic textiles, fishing gear and other plastic products. Sunlight, heat, wind and waves can make larger debris brittle and break it into smaller pieces. Microplastics can move with rivers, stormwater, wastewater, wind and runoff, reaching oceans, lakes, soils and the air. Some particles are intercepted in wastewater treatment or sludge, while others can pass through treatment or enter the environment by other routes.

Microplastics have been reported in marine and fresh waters, beaches, sediments, sea ice, soils and air. Their small size makes ingestion possible for organisms ranging from plankton to larger animals. Laboratory studies have reported adverse effects in some aquatic organisms, but the levels at which risks occur and the importance of particular effects in natural populations remain uncertain. Potential effects may depend on particle characteristics and exposure, and laboratory findings require careful interpretation before they are generalized to wild populations. The detection of particles alone does not establish the scale of ecological harm.

People may encounter microplastics through food, drinking water and inhaled air. The presence of particles in an exposure pathway does not by itself show that a particular dose causes disease. The World Health Organization has reviewed evidence on microplastics in drinking water and separately assessed dietary and inhalation exposure to nano- and microplastic particles. These assessments identify gaps in the available evidence and research needs; health implications remain an area of investigation rather than a settled conclusion.

Comparisons between studies depend on consistent sampling, size cut-offs, identification techniques and reporting, and standard methods continue to be developed. Responses can target the full life cycle of plastics: designing products that shed less, reducing avoidable releases, improving waste handling, and capturing particles in wastewater, stormwater or road runoff. The OECD has examined textiles and tyres as important sources of unintentionally released microplastics and describes source-directed, use-oriented, end-of-life and treatment measures. Because sources are diffuse and uncertainties persist, monitoring and further research are important alongside prevention and mitigation.