What is micropollution and why is it a concern for the environment and human health?

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Plastics are some of the most versatile man-made products. Being durable and lightweight, they've integrated into nearly every facet of everyday life - from food packaging to toiletries to vehicles to textiles. However, the resulting proliferation of plastic use has come with the significant downside – microscopic fragments of plastic accumulating in the environment (this development can be referred to as micropollution). The growing presence brings risks for ecosystems and human health, which are briefly outlined in this article.  

 

Sources of micropollution

Microplastics can be defined as plastics smaller than 5mm (approximately the length of an average red ant)1. Microplastics can either enter the environment at the micro-sized scale (primary microplastics) or fragment from larger, ‘macro’-sized plastics already in the environment (secondary microplastics). Primary microplastics manufactured at the micro-scale are typically used in industrial and domestic products including cosmetics, cleansers/exfoliators, and air-blasting media, as well as preproduction pellets for plastic production. Secondary microplastics are plastic fragments resulting from the mechanical, chemical, or biodegradation of larger plastic debris, such as the particles resulting from the breakdown of plastic bags2.

Microfibres are generally defined as any natural or synthetic microscopic fibres shed from textiles or related fibre-based products, with a size only about 1/5 the diameter of a human hair3. All textiles shed microfibres, including natural (derived from plants and animals), synthetic (derived from plastics) and semi-synthetic  (artificially produced plant-based) textiles. Clothes and textiles are the main sources of microfiber pollution4; however microfibers also come from a range of industrial textile applications5:

  • Industrial textiles (e.g. carpets)
  • Home textiles (e.g. bedding furniture, towels)
  • Automotive textiles (e.g. seating fabric)
  • Geotextiles (e.g. those used in construction)
  • Cigarettes
  • Fishing lines and nets
  • Personal care products.

Micropollution as environmental and human health hazard 

The key characteristics of micropollutants which pose danger to humans and the environment

  • Small size that facilitates widespread distribution in the environment
  • Lack of biodegradability
  • Negative impacts on the environment and human health.

 

Distribution in the environment

Microplastics and microfibres have been found in virtually every type of habitat on the planet, including the deep ocean6, on coastlines7, in Artic seawater8, in freshwater lakes and rivers9, in soil10, on mountaintops11, and in the air12. The abundance of micropollutants in the marine environment has been particularly well-documented:

  • The Indian Ocean has approximately 4 billion microfibres per square km of sediment13
  • Synthetic microfibres account for over 90% of the microplastic pollution identified in Arctic seawater14
  • The most commonly found type of synthetic microfibre in the ocean is polyester15.

Local geographical conditions can impact micropollution levels. For example, the Mediterranean Sea has been found to contain relatively high concentration of microfibres, despite the fact that it is remote from the largest pollution entry points, such as Asia and the US. This could be due to the Mediterranean Sea having the lower exchange and flow of water (it being a more closed water system compared to the other basins), resulting in higher pollution accumulation.

Lack of biodegradability

Biodegradation ultimately depends on how accessible the micronutrients of an item are to the microorganisms in the environment. Due to their unique molecular properties, plastics are fairly resistant to biodegradation16. Plastics are largely broken down in the environment by chemical and physical factors including UV radiation, temperature, and abrasion, and as a result may take hundreds of years to decompose. Microfibres also biodegrade slowly under natural conditions, if at all. Although natural and semi-synthetic fibres degrade faster than synthetic fibres, the speed of degradation between different polymers is currently under-researched17.

Existing evidence indicates that:

  • A polyester fabric remained largely intact after 100 days both in laboratory conditions and in a composting environment18
  • Natural microfibres and some semi-synthetics can biodegrade under the right conditions, and may degrade within weeks to months (e.g. natural fibres may be more likely to degrade in warm, moist environments in the presence of microorganisms and chemical, photochemical and mechanical abrasive forces)19
  • Almost 80% of the microfibres identified in various oceanic basins are cellulosic (i.e. cotton, linen and regenerated cellulose like rayon and viscose) - this suggests that natural and semi-synthetic fibres may persist in the environment longer than we would expect them to20. One reason that cellulosic fibres may persist in the environment is because textiles often contain residues of chemicals used in fibre production and textiles processing that can interfere with the nutritional value of the fibre to microorganisms21. However, the extent to which these chemicals can interfere with the deterioration of different materials remains an open question.

Lack of biodegradability in micropollutants presents a problem because they:

  • Continue to accumulate in the environment
  • Can serve as breeding grounds for pathogens22
  • Can act as concentrators for contaminants such as metals and other chemicals23
  • Can be easily ingested by organisms.


Negative impact on the environment

Once in the environment, microplastics and microfibres can be easily ingested by marine and terrestrial fauna. In marine environments, crustaceans (such as krill, shrimps, crabs) , shellfish, zooplankton, and fish often mistake micropollutants for food24. Over one third of UK-caught fish were found to contain microplastics in their gastrointestinal tracts. Due to their size and shape, microfibres are significantly more likely to be ingested - nearly half of the microplastics found in the guts of common tropical fish were microfibres25.

Micropollutants also move up the food chain and eventually contaminate human food: microplastics and microfibres have been found in bottled water, tap water, beer, salt, shellfish, fish, birds, vegetables, and fruit26. Humans are estimated to consume between 39-52 thousand microfibre particles per year, and to inhale between 35-69 thousand particles (mostly fibres), although these figures are likely to be underestimated27. These estimates roughly equate to consuming, either through ingestion or through inhalation, a paper clip’s worth of microfibres annually28.

 

An arrow worm in the plankton has eaten a plastic microfibre that has blocked the passage of food through its gut.

Copyright: Richard Kirby

While the effects of micropollution are still not fully understood, there is some evidence of negative impact:

  • In the aquatic species, microfibre exposure has been linked to endocrine disruption, toxicity, gut blockages, reduced reproduction and death; the uptake of microplastics allows for the transfer of innate and adsorbed toxins into the organism, which can affect reproduction, impair development, and induce genetic aberrations in invertebrates, fish and amphibians29
  • the ingestion of prey containing microplastics by organisms on the higher levels of the food chain  (i.e. ‘indirect ingestion’ or ‘secondary poisoning’) can lead to the bioaccumulation of toxic chemicals30
  • For humans, microplastics can be consumed through the ingestion of contaminated shellfish and fish, but also from some canned foods, honey, sugar, table salt, root crops, leaf crops, meat, and beverages including milk, drinking water, and beer31; humans are also exposed to inhalation of airborne particles and dermal exposure. Atmospheric microfibre exposure has been linked to respiratory complications, as well as reproductive, carcinogenic, and mutagenic effects32.

There has been limited research on the effects of microplastics on terrestrial organisms, although similar exposure pathways are likely to exist on land, as soil organisms, including earthworms and collembola, have been shown to carry microplastics in their gastrointestinal tracts33.

Micropollution can also cause negative economic impacts on the tourism and fishing industries: tourists may avoid engaging in water-based recreational activities or consuming local seafood in regions where microplastic pollution is a problem.

Observed effects on microfibre exposure on organisms and humans
Effects on organisms Effects on humans
Reduced growth‚ reproduction and survival of water fleas and amphipods34 Respiratory complications‚ including obstructive lung disease43
Gut blockages and nutritional deficiency in fish35 Endocrine disruption and cancer (from bisphenol A (BPA))44
Reduced feeding in mussels‚ worms‚ and crabs36 Inflammation and fibrosis45
Reduced growth in crabs37 Reproductive dysfunction‚ cancer and mutations caused by plasticisers46
Toxicity and mortality in zooplankton38 Microplastics could permeate biological membranes and enter organs47
Translocation to organs after consumption in crabs39 Presence in lung tissue49
Toxicity and endocrine disruptions40 Found in placenta50
Impaired development and reproduction in invertebrates‚ fish and amphibians caused by plasticisers41
Bioaccumulation of toxins in larger organisms through indirect digestion42
Crossing the brain barrier in mice48

Observed effects on microfibre exposure on organisms and humans

Reduced growth‚ reproduction and survival of water fleas and amphipods34

Effects on humans
Respiratory complications‚ including obstructive lung disease43

Gut blockages and nutritional deficiency in fish35

Effects on humans
Endocrine disruption and cancer (from bisphenol A (BPA))44

Reduced feeding in mussels‚ worms‚ and crabs36

Effects on humans
Inflammation and fibrosis45

Reduced growth in crabs37

Effects on humans
Reproductive dysfunction‚ cancer and mutations caused by plasticisers46

Toxicity and mortality in zooplankton38

Effects on humans
Microplastics could permeate biological membranes and enter organs47

Translocation to organs after consumption in crabs39

Effects on humans
Presence in lung tissue49

Toxicity and endocrine disruptions40

Effects on humans
Found in placenta50

Impaired development and reproduction in invertebrates‚ fish and amphibians caused by plasticisers41

Effects on humans

Bioaccumulation of toxins in larger organisms through indirect digestion42

Effects on humans

Crossing the brain barrier in mice48

Effects on humans


How significant is the problem? The current scale and the projected pace of micropollution

Micropollution projections vary; based on available data, we estimate that around 1-5.6 million metric tonnes (MMT) could enter the environment every year. Given their microscopic size, this is a material volume of pollution – the higher estimates reach over 10% of global annual mismanaged plastic waste50. The global release of microplastics into the ocean is estimated to be between 0.8 and 2.5 million tonnes per year,.

Despite these concerns, microplastic and microfibre pollution is still largely unregulated51. If left unaddressed, growth in textile consumption is likely to exacerbate it even more. By 2030, with the continuing increase of global apparel consumption and fibre production, annual microfibre release into the environment could increase by 54% by 2030 (or to approximately 0.5 – 6.0 MMT per annum)52. Another estimate suggests that further 22 MMT of synthetic microfibres could enter the environment by 205053. Microplastic pollution can also be expected to grow, as the production of many microplastics sources, especially vehicle tyres and pre-production plastics, is projected to increase over the next 15 years54.

For a detailed overview of the challenges and potential solutions to micropollution, please see the SII reports on microfibers https://www.firstsentier-mufg-sustainability.com/research/Microfibres.html and microplastics pollution https://www.firstsentier-mufg-sustainability.com/research/microplastics-05-2020.html.

 

 

References

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