There are two categories of micro-plastics: primary (which include microfibers from clothing and micro-beads from cosmetic products) and secondary (which are broken-down particles from larger plastic items including water bottles caused by natural weathering process such as sun radiation and ocean waves).
In 2014, it was estimated that there are between 15 and 51 trillion individual pieces of micro-plastic in the world’s ocean, which was estimated to weigh between 93,000 and 236,000 metric tons.
According to a 2017 IUCN report, micro-plastics are a bigger source of marine plastic than visible pieces of marine litter and could contribute up to 30% of the Great Pacific Garbage Patch.
Textiles, types and city dust account for over 80% of all micro-plastic pollution in the environment.
Due to the small size of microbeads, wastewater treatment plants can only remove an average of 95 – 99.9% of microbeads, leaving an average 0-7 micro-beads per liter being discharged. A 2015 study estimates that around 8 trillion microbeads per day are emitted into the aquatic habitats in the United States, equivalent to the size of 300 tennis court is these microbeads are lined side by side.
Micro-plastics enter the ocean through various pathways, including deterioration of road paints and tyre wear, plastic pellets spilled from shipping containers, synthetic textiles dumped into the ocean, and cosmetic discharges and laundry products entering sewage water.
Some micro-plastics remain on the ocean’s surface. According to a 2017 study, micro-plastics account for 92% of plastic debris on the ocean surface.
Some micro-plastics sink to the ocean floor. A 2020 study estimates that there are 14 million metric tons of micro-plastics on the ocean floor.
Some micro-plastics leave the sea and enter the air according to a 2020 study. Airborne micro-plastics have been detected both in doors and outdoors, as well as can be transported to remote areas through wind according a 2019 study.
Micro-plastics can enter human body via food (packaging and sea food), air and drinking water and potentially causes negative health consequence when reach a certain dose. Micro-plastic can also act as a carrier for pathogens as well as heavy metal by absorbing pollutants into its surface.
A 2020 study from University of Arizona finds micro-plastics in all 47 human tissues studied. In December 2020, micro-plastics were found in the placentas of unborn babies for the first time.
One study suggests that 93% of the bottle water from 11 different brands showed micro-plastic contamination. Compared to water from taps, water from plastic bottles contained twice as much micro-plastics.