Microplastics are essentially very small pieces of plastic which their length is between one nanometer to five millimeters according to the U.S. National Oceanic and Atmospheric Administration (NOAA).
Microplastics are not a specific type of plastic, It's every type of plastic we can find in our ecosystem including some sources like cosmetics, clothing, industrial processes and 3D printing. There are two classifications of microplastics which are primary and secondary.
Primary microplastics are the plastics that are in our environment and the given range above. They are manufactured as microbeads, capsules, fibers or pellets. To give some examples to microplastics, microbeads are small pieces of polyethylene plastic used in cosmetics and personal care products such as some cleaners and toothpaste, industrial scrubbers used for abrasive blast cleaning, microfibers used in textiles and resin pellets(also known as nurdles) used in plastic manufacturing processes.
Secondary microplastics are the small plastic pieces that are a result of larger pieces of plastics breaking down into smaller pieces. When the larger piece of plastic products enter the natural environment degradation process begins. Such products are soda bottles, fishing nets and plastics bags.
Primary and Secondary microplastics both are recognized to persist in the environment at high levels, particularly in aquatic and marine ecosystems. Besides, plastics degrade slowly, often over hundreds if not thousands of years. This increases the probability of microplastics being ingested and incorporated into and accumulated in, the bodies and tissues of many organisms. The entire cycle and movement of microplastics in the environment are not yet known, but research is currently underway to investigate this issue.
Nanoplastics are less than 1 μm (1000 nm) or less than 100 nm in size. The occurrence of nanoplastics in the environment is under debate since disclosure and quantification in environmental models endures a challenge. Speculations over nanoplastics in the environment range from it being a temporary byproduct during the fragmentation of microplastics to it being an invisible environmental threat at potentially high concentrations. The presence of nanoplastics in the North Atlantic Subtropical Gyre has been confirmed and recent developments in Raman spectroscopy and nano fourier transform infrared (nano-FTIR) technology are promising answers soon regarding the nanoplastic quantity in the environment.
They are considered to be a risk to environmental and human health. Due to their small size, nanoplastics can cross cellular membranes and affect the functioning of cells. Nanoplastics are lipophilic and models show that polyethylene nanoplastics can be incorporated into the hydrophobic core of lipid bilayers. Nanoplastics are also shown to cross the epithelial membrane of fish accumulating in various organs including the gall bladder, pancreas, and the brain. Little is known on the adverse health effects of nanoplastics in organisms including humans. In zebrafish, polystyrene nanoplastics can induce a stress response pathway changing glucose and cortisol levels, which is potentially tied to behavioral variations in stress phases.