Microplastics primarily originate from the fragmentation of larger plastic debris, whereas nanoplastics can also be produced directly through industrial processes or by digestive fragmentation in marine organisms.

While microplastics form mostly as secondary pollutants from the breakdown of macroplastics, nanoplastics have multiple origins. Antarctic krill, for example, can physically fragment ingested microplastics into nanoplastics during digestion, introducing a biological pathway for size reduction. Additionally, industrial manufacturing processes may release engineered nanoplastics. This diversity in sources complicates tracing particle provenance and assessing environmental accumulation.