Micro/Nanoplastic Sources within the Environment
Micro/nanoplastics can be released into the environment, either as primary or secondary plastics as described earlier. These plastics can be found on land or in freshwater or marine environments.
Micro/Nanoplastics on Land
The majority of plastics manufactured are being used in consumer products. Increased plastics on land are majorly due to improper waste management, which includes loss during the waste disposal chain, industrial spillages or release from landfill sites. These items can degrade to form secondary micro/nanoplastics within the environment. Micro/ nanoplastics may also be released directly to land along with sewage sludge applied to agricultural land as a fertilizer [14-16].
Micro/Nanoplastics in the Freshwater Environment
Freshwaters such as lakes, rivers, ditches, streams and ponds represent the most complex systems regarding micro/nanoplastic transport and retention. They receive plastics from the land and produce micro/nanoplastics through break up of larger items. Larger plastic items can enter the freshwater environment through inadequate waste disposal, either through littering or loss from landfill or through transport from land via wind or surface runoff [17,18].
Micro/Nanoplastics in the Marine Environment
Sources of micro/nanoplastics to marine environments are widespread, as oceans are generally considered to be the ultimate sink for all plastic within the environment. In addition to the inputs from rivers, plastics will also enter oceans directly via mismanaged waste, including abandoned fishing gear, accidental cargo loss and illegal dumping. This will most likely be in the form of plastic waste that will degrade to form micro/nanoplastics within the marine environment. Micro/nanoplastics are prevalent throughout various locations and even within marine organisms worldwide, with ocean currents leading to specific areas of accumulation such as the well-known “Great Pacific Garbage Patch” [19-21].
Microplastics in the Atmosphere
Owing to the lightweight nature of plastic, many micro/nanoplastic particles remain suspended and transported within the air as “urban dust.” These commonly originate from road dust (e.g., tire and paint particles) and fibers from synthetic textiles, especially from soft furnishings, and can lead to deposition of microplastics to land or aquatic environments. Although urban dust will originate especially in cities and densely populated areas, air currents and wind can carry plastic particles to other regions far from the source [22-25].