Microplastics

Unique identifier / Notation

CH0014

Synonyms

Nanoparticles

Marine debris

Microplastics are small plastic pieces less than five millimetres in length which can be harmful to the environment especially marine life. They originate from a variety of sources, including larger plastic debris that degrades into progressively smaller pieces (adapted from UNEP, 2016 and NOAA, no date).

Primary reference(s)

UNEP, 2016. Marine plastic debris and microplastics: Global lessons and research to inspire action and guide policy change. United Nations Environment Programme (UNEP). Accessed 14 October 2020.

NOAA, no date. What are microplastics? National Oceanic and Atmospheric Administration (NOAA). Accessed 14 October 2020.org/handle/20.500.11822/7720?show=full Accessed 14 October 2020.

Additional scientific description

Microplastics are routinely defined as small particles or fragments of plastic measuring less than 5 mm in length. Some microplastics are intentionally manufactured for industrial and domestic purposes (‘primary’ microplastics). These include ‘microbeads’ used in cosmetic and personal healthcare products, such as toothpaste. ‘Secondary’ microplastics are created by the weathering and fragmentation of larger plastic objects. Weathering and fragmentation are enhanced by exposure to ultraviolet (UV) irradiation. These processes become extremely slow in the absence of UV radiation, as is the case in much of the ocean. Plastics marked as ‘biodegradable’ degrade more slowly in the ocean (UNEP, 2016).

Nanoparticles are a form of marine debris, the significance of which is only now emerging. They are minuscule particles with dimensions of 1 to 100 nanometres (a nanometre is one millionth of a millimetre).

A large proportion of the nanoparticles found in the ocean are of natural origin. It is the anthropogenic nanoparticles that are of concern. These originate from two sources: (i) nanoparticles created intentionally for use in industrial processes and cosmetics and (ii) from the breakdown of plastics in marine debris, from fragments of artificial fabrics discharged into urban wastewater, and through leaching from land-based waste sites (NOAA, 2021).

Recent scientific research has highlighted the potential environmental impacts of plastic nanoparticles. For example, they appear to reduce primary production and the uptake of food by zooplankton and filter-feeders. Nanoparticles of titanium dioxide, which is widely used in paints and metal coatings and in cosmetics, are of particular concern. When nanoparticles of titanium dioxide are exposed to UV radiation from the sun, they transform into a disinfectant and have been shown to kill phytoplankton, which are the basis of primary production in the ocean. The scale of the threat from nanoparticles is unknown, and further research is required (UN, 2017).

About half the global population lives within 100 km of a coastline, and population growth is greatest in that zone. This means the amount of plastic debris entering the ocean from land-based sources is likely to increase unless significant changes are made to waste management practices on land (UNEP, no date).

Metrics and numeric limits

Not available.

Key relevant UN convention / multilateral treaty

The International Convention for the Prevention of Pollution from Ships (MARPOL) is the main international convention covering prevention of pollution of the marine environment by ships from operational or accidental causes (IMO, 1996). The MARPOL Convention was adopted on 2 November 1973. The Protocol of 1978 was adopted in response to a spate of tanker accidents in 1976–1977. As the 1973 MARPOL Convention had not yet entered into force, the 1978 MARPOL Protocol absorbed the parent Convention. The combined instrument entered into force on 2 October 1983. In 1997, a Protocol was adopted to amend the Convention and a new Annex VI was added which entered into force on 19 May 2005. MARPOL has been updated by amendments through the years.

The Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972, the ‘London Convention’ for short, is one of the first global conventions to protect the marine environment from human activities and has been in force since 1975 (IMO, 1972). Its objective is to promote the effective control of all sources of marine pollution and to take all practicable steps to prevent pollution of the sea by dumping of wastes and other matter. Currently, 87 States are Parties to this Convention.

Examples of drivers, outcomes and risk management

To better assess human health risks and inform management actions, a number of research gaps need to be filled. With respect to exposure, there is a need to better understand microplastics occurrence throughout the water supply chain, using quality-assured methods to determine the numbers, shapes, sizes, composition and sources of microplastics and to better characterise the effectiveness of water treatment. Research is also needed to better understand the significance of treatmentrelated waste streams as contributors of microplastics to the environment.

With respect to potential health effects, quality-assured toxicological data are needed on the most common forms of plastic particles relevant for human health risk assessment. Further, a better understanding is needed on the uptake and fate of microplastics and nanoplastics following ingestion. Finally, given that humans can be exposed to microplastics through a variety of environmental media, including food and air, a better understanding of overall exposure to microplastics from the broader environment is needed (WHO, 2020).

The human health risk from microplastics in drinking-water is a function of both hazard and exposure. Potential hazards associated with microplastics come in three forms: the particles themselves which present a physical hazard, chemicals (unbound monomers, additives, and sorbed chemicals from the environment), and microorganisms that may attach and colonise on microplastics, known as biofilms. Based on the limited evidence available, chemicals and microbial pathogens associated with microplastics in drinking-water pose a low concern for human health. Although there is insufficient information to draw firm conclusions on the toxicity of nanoparticles, no reliable information suggests it is a concern (WHO, 2020).