I'm not sure they are. Microplastics have been found in snow[1] and in "oceans, air and food supply"[2]. Additionally, the so-called forever chemicals (PFAS) originated with PTFE (Teflon) plastic, and PFAS 'forever chemicals' are used to produce polymers used in plastics, rubber and fabrics so they are intimately linked with plastics and microplastics.
