Microplastics are tiny plastic particles less than 5 millimeters in diameter that originate either as “primary” microplastics—manufactured pellets, microbeads in cosmetics, and synthetic textile fibers—or as “secondary” fragments created when larger plastic items weather and break apart. Because of their small size and buoyancy, they can travel long distances and are hard to capture once released into the environment.

In aquatic systems, microplastics are now ubiquitous: they float on the surfaces of oceans, lakes, and rivers, mingle in the water column, and accumulate in deep‑sea and estuarine sediments. Ocean currents disperse them across the globe, so they are found from crowded coastal zones to remote mid‑ocean gyres, Arctic ice, and even the Mariana Trench. Freshwater bodies, stormwater runoff pathways, and wastewater effluent streams all act as conduits that deliver these particles to marine environments.

On land, microplastics have been detected in agricultural soils (often introduced via sewage sludge used as fertilizer), roadside dust from tire and brake wear, and landfill leachate. Airborne fibers drift onto mountain snowfields and urban rooftops alike, while microplastics also show up in drinking water, bottled beverages, table salt, and many foods. Their pervasive presence across air, water, and soil illustrates how thoroughly plastics have infiltrated every corner of the planet.