Sources of microfibers and their distribution in the environment

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Microfibers can be defined as any natural or synthetic microscopic fibres shed from textiles or related fibre-based products. Such particles are with a size of only about 1/5 the diameter of a human hair. Microfibres are estimated to be a key contributor to micropollution and its accumulation in the environment, and have been linked to significant risks to the environment and human health. This article outlines the main sources of microfibers and their distribution in the environment. 

Microfibers enter the environment via three main channels: 

  • wastewater releases from textile manufacturing and laundering 
  • atmospheric releases from textile manufacturing, and textile use 
  • terrestrial releases from improperly disposed textiles releasing microfibres directly into the soil. 

The relative contribution of each of those pathways is not well understood. Fibre shedding during the use phase, and washing, in particular, is more researched than shedding during the manufacturing and end-of-life phases. The contribution of synthetic microfibres also appears to be better researched compared to that of natural microfibres.

 

Internally estimated microfibre release through the textile lifecycle (synthetic and natural fibres)

Despite scarce quantifiable data, the following areas are worth a mention in understanding better the drivers of microfibre pollution:

  • the textile manufacturing process
  • textile maintenance and use
  • textile composition and weave
  •  wastewater treatment.


Textile manufacturing

Microfibres are released through various stages of textile production due to the abrasive processes associated with dyeing, printing, and finishing textiles1. The volume of resulting microfibre losses is generally unknown; an estimate suggests that 10% to 15% of the textile mass is lost during the clothing production process2. This would represent around 10-16 million metric tonnes (MMT) of loss for 2020 alone (based on 109 MMT global fibre production for 20203 . However, not all of these microfibres would be released into the environment - a proportion of them could be captured during the manufacturing process (e.g. through air filtration).

Simplified supply chain for textile manufacturing
 


Textile maintenance and use

Microfibre shedding during textile maintenance and use is affected by several factors including:

Maintenance - As fabrics are washed and dried, microfibres detach due to chemical and mechanical abrasion4. Microfibres are then rinsed from the textiles and discarded in wastewater or emitted into the air, in the case of dryers. The number (and volume) of microfibres that are released with every load of laundry varies widely and depends in part on the contents of the wash. The estimates of the total number of microfibres produced per wash range from 700,000 to 1.5 million to 7 million5. In terms of volume, approximately 0.5-1.3 grams of microfibres are expected to be released in every wash and it is estimated that the average household in North America releases approximately 135g of microfibres via its laundry every year6. Estimates of global synthetic microfibre release from washing clothes range from 0.18 MMT to 0.36 MMT to 0.50 MMT annually7. We further estimate that synthetic and natural microfibre release from laundry could be in the range of 0.12-1.07 MMT annually.

Factors that increase microfibre loss during washing include:

  • use of powder detergent8
  • use of top-loading washers9
  • drying clothes using tumble dryers10

Use - Although most studies on microfibre shedding have focused on microfibre loss during washing, it has been suggested that textiles may shed as many microfibres when they are being worn as when they are being washed11. For example, a study estimated that between 3-10 metric tonnes of microfibres would fall on an urban area the size of Paris every year via atmospheric deposition12.

Textile / garment age - Garment age may also have an impact on shedding rates depending on the composition of the garment in question. For example, aging may increase shedding rates in certain blends but decrease them in others13.


Textile composition and weave

Different types of textiles and fibres shed microfibres at different rates, meaning some types of textiles contribute to microfibre pollution more than others. Natural fibres, such as cotton and wool, tend to shed more than synthetic ones and among the synthetic and semi-synthetic textiles, polyester typically sheds more than nylon14. Post 2010, polyester accounted for over 50% of the global fibre production15.

The textile weave also considerably affects shedding rates: fabrics with a greater number of exposed filaments (such as fleece), tend to shed more compared to those with fewer (such as kmit or woven fabrics).

 

Shedding rates across major textile categories

Shedding rates across textile weave patterns

Source: Vassilenko et al. (2021)
Individual sample date depicts the average weight of lint over three laundry washes. Standard deviations are not pictured but vary between 1-61% for all samples. Category medians are calculated based on averages for the samples within a given subcategory. Two outlier samples are excluded for both the chart and the calculation of the category medians [polyester/fleece (778 mg lint/kg wash) and mixed fabrics/knit spun staple (838 mg lint/kg wash).


Wastewater treatment

Residential and commercial wastewater can be sent to wastewater treatment plants for processing before the decontaminated effluent is released back into the environment. Therefore, wastewater treatment can act as a barrier for microfibres, but its effectiveness depends on several factors including:

Connectivity to wastewater treatment infrastructure - Less than a third of the human population is connected to wastewater management infrastructure, and an estimated 80% of wastewater globally is released into the environment without sufficient treatment16. Therefore, there is often no mechanism to remove waste products from the effluent before it reaches the environment. 

Capture efficiency of wastewater treatment processes - Although modern wastewater treatment processes were not designed to filter out small buoyant particles, the capture efficiency of wastewater treatment plants (WWTPs) is relatively high, often higher than 90%17. However, given these plants' large volumes of wastewater, the resulting volume of microfibres entering the environment from WWTP effluent can still be large.
WWTPs typically have primary, secondary, and tertiary treatment processes, although this depends on the location of the plant and the intended end use for the treated water18. Microparticles, such as microfibres and microplastics, appear to mostly be removed during primary treatment (the sludge settling and skimming processes)19.

Application of sludge to agricultural lands - Removing microfibres from wastewater effluent by sequestering them in sewage sludge does not necessarily prevent them from entering the environment. This is because sewage sludge, a semi-solid by-product from wastewater treatment that is high in nutrients, is frequently applied to agricultural lands in North America and Europe as fertiliser20. The sludge could be also incinerated, sent to a landfill, or added to cement, with varying degrees of success in retaining microfibres21. For example, roughly 93% of the WWTP sludge produced in the UK is applied to agricultural or other lands, while 4% is incinerated and 3% is used in industry22. In addition, untreated or minimally treated wastewater can be used in irrigation, also leading to the application of microfibres and other contaminants to terrestrial systems23.

As research regarding microfibre shedding advances, it will be important to improve our knowledge of the microfibre shedding potential along the entire textile lifecycle. Understanding all sources and drivers of pollution, including their relative contributions, will facilitate the identification and adoption of effective pollution prevention.

 

 

References

1 The Nature Conservancy & Bain & Company. Toward eliminating pre-consumer emissions of microplastics from the textile industry. (2021).

2 Gavigan, J., Kefela, T., Macadam-Somer, I., Suh, S. & Geyer, R. Synthetic microfiber emissions to land rival those to waterbodies and are growing. PLoS One 15, 1–13 (2020).

3 Textile Exchange. Preferred Fiber & Materials Market Report 2021. 1–118 (2021).

4 De Falco, F., Di Pace, E., Cocca, M. & Avella, M. The contribution of washing processes of synthetic clothes to microplastic pollution. Sci. Rep. 9, 6633 (2019).

5 Napper, I. E. & Thompson, R. C. Release of synthetic microplastic plastic fibres from domestic washing machines: Effects of fabric type and washing conditions. Mar. Pollut. Bull. 112, 39–45 (2016); De Falco, F., Di Pace, E., Cocca, M. & Avella, M. The contribution of washing processes of synthetic clothes to microplastic pollution. Sci. Rep. 9, 6633 (2019); Vassilenko, E. et al. Domestic laundry and microfiber pollution: Exploring fiber shedding from consumer apparel textiles. PLoS One 16, 1–17 (2021).

6 Eunomia and ICF. Investigating options for reducing releases in the aquatic environment of microplastics emitted by (but not intentionally added in) products. (2018); Vassilenko, P. K., Watkins, M., Chastain, S., Posacka, A. & Ross, P. S. Me, My Clothes and the Ocean: The role of textiles in microfiber pollution. https://assets.ctfassets.net/fsquhe7zbn68/4MQ9y89yx4KeyHv9Svynyq/8434de64585e9d2cfbcd3c46627c7a4a/Research_MicrofibersReport_191004-e.pdf (2019).

7 Belzagui, F., Crespi, M., Álvarez, A., Gutiérrez-Bouzán, C. & Vilaseca, M. Microplastics’ emissions: Microfibers’ detachment from textile garments. Environ. Pollut. 248, 1028–1035 (2019); Gavigan, J., Kefela, T., Macadam-Somer, I., Suh, S. & Geyer, R. Synthetic microfiber emissions to land rival those to waterbodies and are growing. PLoS One 15, 1–13 (2020); Ellen MacArthur Foundation. A New Textiles Economy: Redesigning Fashion’s Future. https://www.ellenmacarthurfoundation.org/assets/downloads/publications/A-New-Textiles-Economy_Full-Report_Updated_1-12-17.pdf%0Ahttps://www.ellenmacarthurfoundation.org/publications/a-new-textiles-economy-redesigning-fashions-future (2017).

8 Carney Almroth, B. M. et al. Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment. Environ. Sci. Pollut. Res. 25, 1191–1199 (2018); Hernandez, E., Nowack, B. & Mitrano, D. M. Polyester Textiles as a Source of Microplastics from Households: A Mechanistic Study to Understand Microfiber Release during Washing. Environ. Sci. Technol. 51, 7036–7046 (2017).

9 Hartline, N. L. et al. Microfiber Masses Recovered from Conventional Machine Washing of New or Aged Garments. Environ. Sci.Technol. 50, 11532–11538 (2016).

10 Pirc, U., Vidmar, M., Mozer, A. & Kržan, A. Emissions of microplastic fibers from microfiber fleece during domestic washing. Environ. Sci. Pollut. Res. 23, 22206–22211 (2016).

11 De Falco, F., Cocca, M., Avella, M. & Thompson, R. C. Microfiber Release to Water, Via Laundering, and to Air, via Everyday Use: A Comparison between Polyester Clothing with Differing Textile Parameters. Environ. Sci. Technol. 54, 3288–3296 (2020).

12 Dris, R., Gasperi, J., Saad, M., Mirande, C. & Tassin, B. Synthetic fibers in atmospheric fallout: A source of microplastics in the environment? Mar. Pollut. Bull. 104, 290–293 (2016).

13 De Falco, F., Di Pace, E., Cocca, M. & Avella, M. The contribution of washing processes of synthetic clothes to microplastic pollution. Sci. Rep. 9, 6633 (2019); Carney Almroth, B. M. et al. Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment. Environ. Sci. Pollut. Res. 25, 1191–1199 (2018).

14 Vassilenko, E. et al. Domestic laundry and microfiber pollution: Exploring fiber shedding from consumer apparel textiles. PLoS One 16, 1–17 (2021); Carney Almroth, B. M. et al. Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment. Environ. Sci. Pollut. Res. 25, 1191–1199 (2018).

15 Textile Exchange. Preferred Fiber & Materials Market Report 2021. 1–118 (2021).

16 Boucher, J. & Friot, D. Primary Microplastics in the Oceans: A Global Evaluation of Sources. https://www.iucn.org/content/ primary-microplastics-oceans (2017) doi:dx.doi.org/10.2305/IUCN.CH.2017.01.en; UNESCO & UN-Water. United Nations World Water Development Report 2020:Water and Climate Change. (2020).

17 Eunomia and ICF. Investigating options for reducing releases in the aquatic environment of microplastics emitted by (but not intentionally added in) products. (2018); Nizzetto, L., Futter, M. & Langaas, S. Are Agricultural Soils Dumps for Microplastics of Urban Origin? Environ. Sci. Technol. 50, 10777–10779 (2016); De Falco, F., Di Pace, E., Cocca, M. & Avella, M. The contribution of washing processes of synthetic clothes to microplastic pollution. Nature 9, 6633 (2019); Prata, J. C. Microplastics in wastewater: State of the knowledge on sources, fate and solutions. Mar. Pollut. Bull. 129, 262–265 (2018); Xu, X., Hou, Q., Xue, Y., Jian, Y. & Wang, L. P. Pollution characteristics and fate of microfibers in the wastewater from textile dyeing wastewater treatment plant. Water Sci. Technol. 78, 2046–2054 (2018).

18 FAO. Wastewater treatment and use in agriculture - FAO irrigation and drainage paper 47. http://www.fao.org/3/t0551e/ t0551e08.htm (1992); Carr, S. A., Liu, J. & Tesoro, A. G. Transport and fate of microplastic particles in wastewater treatment plants. Water Res. 91, 174–182 (2016).

19 Carr, S. A., Liu, J. & Tesoro, A. G. Transport and fate of microplastic particles in wastewater treatment plants. Water Res. 91, 174–182 (2016).

20 Carr, S. A., Liu, J. & Tesoro, A. G. Transport and fate of microplastic particles in wastewater treatment plants. Water Res. 91, 174–182 (2016); FAO. Wastewater treatment and use in agriculture - FAO irrigation and drainage paper 47. http://www.fao.org/3/t0551e/ t0551e08.htm (1992).

21 Carney Almroth, B. M. et al. Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment. Environ. Sci. Pollut. Res. 25, 1191–1199 (2018).

22 Biosolid Assurance Scheme. About Biosolids. https://assuredbiosolids.co.uk/about-biosolids/ (2021).

23 5,29 Henry, B., Laitala, K. & Klepp, I. G. Microfibres from apparel and home textiles: Prospects for including microplastics in environmental sustainability assessment. Sci. Total Environ. 652, 483–494 (2019); FAO. Wastewater treatment and use in agriculture - FAO irrigation and drainage paper 47. http://www.fao.org/3/t0551e/ t0551e08.htm (1992).