Plastics that are originally manufactured in a particularly small size for specific applications are called primary microplastics. In the marine environment, plastic debris of every size can be mechanically broken down into smaller pieces by external forces such as UV radiation, wind, waves, or animals. This physical weathering produces secondary microplastics.6,12


Further breakdown of plastic into ever-smaller particles does not lead to a complete degradation into monomers. Instead, the original plastic polymer remains intact at microscopic scale unless the original polymer is converted into carbon dioxide, water, methane, hydrogen, ammonia, and other inorganic compounds, a process of biodegradation influenced by external conditions and the properties of the particular plastic polymer. This generally does not happen to plastics in the aquatic environment.


Microplastics


The term ‘microplastics’ is widely used to describe plastic particles with the size ranging from 1 nanometre to 5 millimetre22


Monomer


into a chain, using a catalyst, to form polyethylene (C2


H4 H4 )n Polymer


Polymers are large organic molecules composed of repeating carbon-based units or chains that occur naturally and can be synthesised. Common natural polymers include chiton (insect and crustacean exoskeleton), lignin (cell walls of plants), cellulose (cell walls of plants), and protein fibre (wool, silk)6


Global plastics production (metric tonnes)


200 220 240 260 280 300 320


Photo Credit: Pressmaster/ Shutterstock.com


38% increase from 2004


Monomers are molecules capable of combining, by a process called polymerisation, to form a polymer. For example, the monomer ethylene (C2


) is polymerised


2004


2007


2009


2011


2012


2013


2014 Data source: PlasticsEurope (2015)


33


UNEP FRONTIERS 2016 REPORT

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