A fibre can be informally defined as a particle in which one of its dimensions is considerably larger than the other two, which are also equal or very similar to each other. However, the precise definition of a fibre in the context of research on plastic contaminants requires additional explanations. The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) considers a synthetic polymer particle to be a microplastic if its larger dimension is below 5 mm and not below 1 µm. This definition does not mention the shape of the particle, so in the case of fibers, the larger dimension corresponds to its length. The fact that fibers are flexible and their length changes with configuration adds an additional complication that is often not taken into account. To avoid ambiguity, the length of a fibre is generally considered to be its maximum length when fully stretched. Therefore, a microplastic fibre is one whose length is less than 5 mm (and greater than or equal to 1 micron) whose main component is a synthetic polymer.
Adding complexity, the Committee for Risk Assessment (RAC) and the Committee for Socio-economic Analysis (SEAC) of the European Chemicals Agency (ECHA) in their proposal to restrict intentionally added microplastics in certain products consider a fibre to be an approximately cylindrical particle whose length is ≤ 15 mm and whose aspect ratio (the ratio of length to diameter) is > 3. (The 3:1 aspect ratio is derived from or coincides with the regulation on asbestos fibers established by the World Health Organization.) As observed, the definition is only partially coincident with the one commonly used in environmental pollution studies.
Furthermore, there is often a curious terminological error consisting of synthetic polymer fibers falling within the size range of microplastics are referred to as ‘microfibers.’ This is a mistake even the GESAMP makes into their reports and that should be avoided because the term ‘microfiber’ has a specific technical meaning. It refers to textile fibers with a thickness of less than 1 decitex (dtex, with 1 tex being the weight in grams of 1000 meters of thread) or, in the United States, 1 denier (weight in grams of 9000 meters of thread). Most commercial microfibers are made of polyester or polyamides, and their diameter is less than 10 µm (thinner than a human hair), although they are obviously only microplastics if their length is not larger than 5 mm.
Synthetic fibers (microplastic fibers) constitute a significant source of microplastic pollution. The release of these fibers from fabrics during their use or washing represents a major source of emissions of synthetic polymers and their additives into the environment. It has been described that these emissions can reach tens of thousands of fibers per gram of fabric in each wash (especially in the initial washes, possibly due to threads trapped inside the fabric during production). This fact and the discussion about how it could be avoided or reduced have become a popular topic in the media. It is known that like other microplastics, these fibers escape relatively easily from wastewater treatment plants and represent a constant flow of contaminants reaching our rivers and seas.
Microplastic fibers not only end up in our waters but also constitute a significant portion of the atmospheric deposition of particulate contaminants. Deposition rates are particularly high in urban centres and in general in areas with higher population density. Deposition rates of over a thousand microplastics per square meter per day have been described in the centre of London, of which the vast majority (> 90%) were microplastic fibers. It is also known that fibers are more mobile than other microplastics, capable of traveling distances of thousands of kilometres carried by atmospheric circulation.
However, fibers whose main component is a synthetic polymer are not the only ones we release to the environment. ISO/TR 11827:2012 (Textiles — Composition testing — Identification of fibres) classifies fibers as natural and manufactured. Manufactured fibers can be synthetic (synthetic polymers) or artificial (made from existing macromolecules in nature such as cellulose, latex, or proteins). Natural fibers encompass a wide range of fibers of animal (silk, wool), plant (cotton, hemp), and even mineral (asbestos) origin. It is important to distinguish artificial fibers (like viscose) from natural ones (like cotton), although they can be chemically quite similar (cotton consists of cellulose, and viscose is regenerated cellulose).
Some scientists consider natural textile fibers as environmental contaminants since their origin is essentially anthropogenic, regardless of whether they come from natural polymers or not. This is because fibers from our clothing can originate from natural macromolecules, but they have undergone industrial processing. As mentioned in a previous post, they are normally treated with or incorporate a variety of chemical additives, which can be synthetic compounds. The risks posed by these fibers are not well understood, but their abundance in the environment has been well documented. Furthermore, all fibers, whether of natural origin or not, can interact with other environmental contaminants, altering their distribution due to their high mobility.
In sum, fibers are a significant source of air and water pollution. They originate from the fabrics we produce, and even natural fibers like cotton must be considered a potential contaminant due to their industrial processing and their ability to interact with other pollutants. Natural fibers that do not have a completely natural origin (such as plant residues, for example) should be regarded as artificial materials, and their dispersion into the environment should be avoided, at least their uncontrolled dispersion. To this end, Directive 2008/98/EC as amended by Directive (EU) 2018/851 and its transposition in the different Member States establish the mandatory separate collection of municipal textile waste by December 31, 2024. This obligation is a result of the constant (and arguably unnecessary) increase in textile production and its extremely low recycling rate.
Science, Plastic and Environment 