Microplastics are defined by the US National Oceanic and Atmospheric Administration as plastic particles smaller than 5mm. The European Chemical Agency (ECHA) further describe microplastics as being resistant to biodegradation and consequently, having a tendency to accumulate in the (marine) environment. ECHA is concerned that safe thresholds for microplastics have yet to be determined, that the level of microplastics may accumulate progressively over time, and that the presence of microplastics in the aquatic environment could theoretically affect organisms in the ecosystem (though conclusive scientific evidence for this is absent).
Microplastic particles are intentionally added to various products (i.e. primary microplastics), including cosmetics, clothing, detergents, medical, agricultural and horticultural products. ECHA has proposed a restriction on the use of intentionally added microplastic particles to any consumer or professional-use product, though this restriction has not been adopted as law. Another potential source is from the degradation of larger plastic material (i.e. secondary microplastics).