Primary microplastics are basically produced in this form and enter the environment as particles smaller than 5 mm. Primary sources can be tiny residues from plastic production. There are products that also contain added microplastics as components. These include fertilizers, pesticides, cosmetics, household and industrial detergents, cleaning products, paints, and many products used in the oil and gas industry [19]. Personal care and cosmetic products, facial cleansers, toothpastes, shaving foams, exfoliants mainly contain polyethylene (PE) and polypropylene (PP) microparticles as additives (e.g. for emulsion stabilization or viscosity adjustment). They also include the grains for special medical purposes (e.g. tooth polishing) as well as the fine grains used by industrial grinders to produce particularly smooth surfaces [9]. After use, these microbeads (a kind of microplastic with a specific function for scrubbing or cleaning) find their way into wastewater, pass through sewage treatment plants and can end up in natural waters [19]. As a result, each year approximately 42,000 tons of microplastics may enter the environment in Europe [20]. In addition, the leaching of granules used as filler material for artificial grass for sports fields is also a primary source; the annual emission can reach 16,000 tons [20].

Secondary sources form from the fragmentation and breakdown of larger plastic items; the particles – produced by the physical, chemical, and biological degradation of macroplastics – are referred to as secondary microplastics [9]. The most significant amount comes from the wastes that have been removed from the landfill or not properly treated in the landfill. In addition, they originate from agriculture, fishing, and the decomposition of hygiene products. Small fibers shedding during the washing of man-made textiles and synthetic fabrics [19], as well as small pieces coming from worn tires/brake shoes end up in the wastewater or in the air. The use of synthetic polymer-based (dispersion) paints, the release of unused paints in landfills/the environment, and the plastic residue in organic waste and laminated paper in paper waste are also secondary sources. It is estimated that approximately 176,000 tons of unintentionally generated microplastic particles enter the surface waters in Europe during the wear and tear of larger plastic products [20].

In 2020, an interesting article was published about the global distribution and extent of pollution caused by synthetic microfibers, the largest primary source of microplastics [19]. Synthetic fibers account for 14% of global plastic production and generate microfibers during their use. Land emissions from synthetic textiles, which are increasing by 12.9% each year, are currently 176,500 tons per year, which already exceeds the annual amount of 167,000 tons that enter the aquatic environment. Gavigan and his colleagues summarize the results of their calculations in a spectacular way (Figure 1).