Plastic falling from the sky

There is also plastic in the atmosphere. It is part of a group of particles known as atmospheric aerosol. These are small solid or liquid particles suspended in the air, with diameters typically ranging from 1 nm to 10 μm (from one nanometre to ten microns). These diameters correspond to nanoscale-sized molecules, such as organic molecules, or to particles like pollen, sand, or salt, which can reach sizes of microns or larger. Atmospheric aerosols are generated in large quantities due to natural phenomena, such as volcanic eruptions or emissions from the surface of the seas, which make up marine aerosol. Furthermore, human activities release a significant amount of aerosols into the atmosphere through the use of both fossil and non-fossil fuels, including biomass combustion, human-caused fires, and industrial, and agricultural activities. In general, the anthropogenic fraction dominates over the natural one, both in rural and urban/industrial areas.

The influence of atmospheric aerosols on climate is well-known. Their impact on human health is also recognized, as particles smaller than 10 µm can be easily inhaled and are potentially harmful to pulmonary and cardiovascular functions. The episodes of smog (an acronym for smoke & fog) that occurred in post-war London due to the combustion of low-quality coal in power plants are outstanding examples. These events culminated in the episode in December 1952 that resulted in several thousand deaths. It’s important to note that particulate matter is not a single pollutant but a complex mixture of different organic and inorganic compounds, in liquid and solid forms. In current air pollution monitoring programs, two ranges of particulate matter are considered: PM10, which consists of particles with a diameter equal to or less than 10 microns, and PM2.5, or fine particulate matter, with a diameter equal to or less than 2.5 microns.

Recently, microplastics have emerged as a component of the anthropogenic aerosols. Microplastics are solid particles of synthetic polymers, with their largest dimension being less than 5 mm. Large microplastics readily sediment, but the smaller ones can remain suspended for prolonged periods. (Their suspension is favoured by the lower density of polymers compared to mineral matter and in the case of non-spherical particles like fibers.) Urban areas are important sources of microplastic emissions into the environment. We release a significant amount of microplastics into freshwater and marine environments through treated wastewater, but they also enter the atmosphere due to the wear and tear of materials such as textiles and other objects made from synthetic polymers. Furthermore, cities facilitate the dispersion of microplastics released into the atmosphere due to the urban heat island effect, which generates upward air currents of relatively warm air. This occurs because cities are built with materials that absorb solar radiation, like asphalt, and they also emit heat due to the operation of heating systems, vehicles, and a wide variety of machinery and electrical devices.

The presence of microplastics in the atmosphere can be quantified using passive or active samplers. Passive samplers (or collectors) are containers that collect atmospheric deposition over a given period. They can be designed to collect dry and wet (during rain episodes) deposition separately or together. Passive samplers allow for the determination of deposition rates in terms of microplastics per square meter per day or equivalent units. Active samplers are filtration systems equipped with a suction pump that passes a certain volume of air through a filter medium. These samplers enable the establishment of the concentration of microplastics per unit volume of air at a specific time and location.

Passive sampler (left) and air filter (right)

There are few data available on the amount of plastic carried by the air in our cities. The diversity of urban, suburban, rural, and remote environments sampled, along with methodological differences between studies, result in significant dispersion in the published data. It has been estimated that the most polluted areas in Asia emit as much as one thousand tons of plastic into the Pacific and Indian Oceans through the atmosphere each year. Our teams (Universities of Alcalá and Autónoma de Madrid and the Centre for Astrobiology CAB-INTA-CSIC) have measured concentrations of microplastics exceeding ten particles per cubic meter in direct samplings using aircraft flying over urban centres at up to 3500 m above the surface. Trajectory analyses indicate that plastic particles can be deposited hundreds of kilometres away from their point of emission.

The figure below shows microplastic deposition rates from recent studies. The figures range from approximately one thousand microplastics per square meter per day measured in central London to values of less than ten microplastics per square meter per day recorded in a remote area in Iran. The significant dispersion of available data (the ordinate axis is in logarithmic scale) is due to the diversity of sampled environments and the use of different characterization techniques: Raman microscopy allows the analysis of particles about ten times smaller than mid-infrared microscopy, leading to a bias towards higher concentrations as smaller particles are always more abundant. Also, quite a few studies only analyse a small fraction of the total collected particles, which may lead to high sampling errors.

Deposition rates of microplastics reported in recent studies (R corresponds to spectroscopic determinations performed using Raman microscopy)

The data for Madrid, Barcelona, Vigo, and Tres Cantos are comparable in terms of methodology, as they come from a larger research project conducted by EnviroPlaNet network groups and recently published in the journal Science of the Total Environment. This study was carried out in ten Spanish cities over four months, one in each of four consecutive seasons. The average deposition rate ranged from 5.6 to 78.6 microplastics per square meter per day, depending on the sampled city. More in Madrid and Barcelona, and less in smaller cities. To put this result into context, the figures obtained correspond to the deposition of over one hundred thousand plastic particles per day on the grass at the Santiago Bernabéu stadium (approximately 50 million microplastics per year). They represent a small mass because they are small particles, ranging from a few tens of microns to less than half a millimetre, with an average size close to that of a human hair’s thickness; but they are there. Most of them are polyester and acrylic fibers, generally of clear textile origin, polyolefins (the most commonly used polymers), and alkyd resins (used in paints).

In summary, the atmosphere carries remnants of our plastic materials, sometimes over long distances from their point of emission, and deposits them at distances that depend on the atmospheric conditions. A significant portion of these plastics consists of textile fibers, and all of them are small-sized particulate matter, small enough to be inhaled, thereby posing risks to human health that are still challenging to assess. For example, these materials are easily colonized by microorganisms, some of which can be pathogens.

Uses of Bioplastics

According to European Bioplastics, the global production of bioplastics is around 2.2 million tons (data from 2022), which represents less than one percent of the over 390 million tons of plastic produced annually (Plastics Europe for 2021, Plastics – The Facts, 2022). Within these 2.2 million tons, approximately one million correspond to non-biodegradable but bio-based plastics, mainly polyethylene (PE), polyamides (PA), and poly(trimethylene terephthalate) (PTT). (These are plastics that don’t differ from conventional ones in anything except the raw materials they are made from.) Also included are slightly less than 100,000 tons of poly(butylene adipate-co-terephthalate), PBAT, a biodegradable but not bio-based polymer. PBAT is an aromatic polyester produced from petrochemical-derived 1,4-butanediol, adipic acid, and dimethyl terephthalate. Other similar polymers, biodegradable but not bio-based and produced in smaller quantities, are polycaprolactone and poly(butylene succinate).

As indicated in a previous post, the most relevant bioplastics are those at the same time bio-based and biodegradable (meaning compostable), which have been referred to as BioCom. This category excludes biodegradable polymers that are not bio-based (PBAT) and those bio-based but not biodegradable (PE, PA, PTT). The global annual production of bioplastics mentioned earlier includes 80,000 tons of regenerated cellulose films (there are other types of industrial cellulose) and 400,000 tons of thermoplastic starch (TPS) (Source: European Bioplastics). The rest of the BioCom polymers amount to 460,000 tons of polylactic acid, PLA, and about 90,000 tons of polyhydroxyalkanoate, PHA. There are other emerging polymers expected to play a significant role in the future, such as poly(ethylene furanoate), but for now, BioCom production is concentrated on the four types mentioned earlier: cellulose, TPS, and the aliphatic polyesters PHA and PLA.

It is still a relatively small production, although projections anticipate sustained growth in the near future. The main commercial bioplastic is PLA, produced by the polymerization of lactic acid or its esters, which in turn can be biotechnologically obtained from raw materials like corn starch or sugarcane. TPS is a blend of two polymers, amylose, and amylopectin, both consisting of a sequence of glucose units. When mixed with water and plasticizers such as glycerol or sorbitol, it becomes a thermoplastic material. Despite its easy obtention (from cereals, legumes, or potatoes) and numerous potential uses, the industrial use of TPS is hindered by its high hydrophilicity (due to the presence of hydroxyl groups) and limited mechanical properties. For this reason, it’s used in blends with various fillers and other polymers, particularly with biodegradable polyesters like PLA or PBAT.

The potential uses of bioplastics are quite extensive, although the majority of current production is concentrated in agricultural applications, particularly in the production of plastic film for mulching, as well as the manufacturing of various types of bags and packaging materials. Another well-established application is the manufacture of biodegradable consumer products that range from tableware (cutlery, cups, and the like) to parts of electronic equipment such as circuit boards or computer casings. Still under development there are various biomedical applications, such as the production of absorbable staples or sutures, and controlled-release capsules (PolyActive by Afinitica). Finally, an area with significant developmental potential is the automotive industry, for uses such as coatings, carpets, and other interior vehicle components.

Main uses of bioplastics (the size of the sectors is proportional to the volume of their production in the EU in 2022 according to European Bioplastics)

Agricultural mulching is currently the primary application of bioplastics. The first use of plastic for mulching (and also as greenhouse covering) took place in the 1950s in the United States, following the work of Professor Emery Myers Emmert from the University of Kentucky, who laid the foundation for plasticulture. Mulches cover the soil around plants, retain moisture, regulate soil temperature, and inhibit the growth of unwanted plants (weeds in agricultural terms), thereby increasing productivity. Over time, films of varying thickness have been developed for different crops, with different colours for different climates or target soil temperatures. The installation and management methods for mulch films have been improved, but the traditional (and cost-effective) polyethylene film has the drawback that it is difficult (generally impossible) to completely recover after harvest. This is because it easily tears off due to its thinness, which can be as fine as 60 microns. Additionally, its use is incompatible with certain mechanical harvesting operations.

Biodegradable mulches are products that disintegrate in the soil at the end of the cultivation period, thereby eliminating the need to remove and recycle mulches made from conventional plastics. Their use not only avoids the costs of collection and waste treatment (complex due to the mixture of soil and crop residues), but also limits soil pollution with plastic fragments. Biodegradable mulches must comply with the EN 17033 standard – Plastics – Biodegradable mulch films for use in agriculture and horticulture, which is complemented by requirements for conventional mulches that need to be recovered after use (EN 13655). Commercial biodegradable mulches are made of biodegradable polymers depending on the manufacturer and may contain TPS, PLA, and PBAT, along with plasticizers, additives such as UV filters, antioxidants, colorants, and various fillers. This category includes BASF’s Ecovio, a blend based on Ecoflex (PBAT) and PLA, and mulches based on Novamont’s Mater-Bi, a material whose most common version contains TPS and PBAT (though Mater-Bi encompasses other formulations as well). These materials currently have a small market share, accounting for 5% of the total mulch market, which in Europe amounts to over 100,000 tons, but their use is expected to follow a growing trend, with global market growth estimated at just under 10% annually until 2030.

Biodegradable bags, packaging, and other materials are made from the same biopolymers mentioned before that can combine with other easily degradable natural substances such as paper, cardboard, and natural fibers. Generally, this type of product only degrades properly in industrial composting facilities, as defined by the harmonized standard EN 13432, which sets specific criteria for packaging to be composted. Only lightweight bags can be compostable in home composting facilities if they meet the recent EN 17427 standard. The composition of these lightweight bags also involves a combination of the aforementioned biopolymers: TPS, PBAT, PLA, and various additives. Finally, biopolymers are used to create a range of items including compostable cutlery, plates, and cups (all subject to EU Directive 2019/904 on the reduction of the impact of certain plastic products on the environment).

It is important to emphasize that not all bioplastics are biodegradable, and those that are biodegradable can generally degrade only in industrial composting facilities. A bioplastic, even if it is biodegradable and not just bio-based, can persist in the environment for years or decades if improperly discarded, so its use should not be trivialized. Lastly, it is important for consumers to be able to distinguish compostable bioplastics (which can be composted along with organic waste) from conventional plastics (among which only packaging is typically recycled), in order to avoid mixing incompatible materials that hinder proper recycling.

How biodegradable are biodegradable plastics?

In a previous post, the different types of bioplastics were introduced. It was shown that bioplastics constitute a family of materials that includes bio-based and biodegradable materials. When both characteristics occur simultaneously, the bioplastic, being both bio-based and compostable at the same time, is referred to as BioCom. It is important to emphasize the distinction between ‘biodegradable’ and ‘compostable’. A biodegradable material is one that can break down through the action of biological agents such as bacteria or fungi over a certain period of time and under unspecified or natural conditions. A compostable material is necessarily biodegradable, but additionally, it must degrade under precisely specified conditions, resulting in a material similar to humus that can serve as fertilizer or organic soil amendment.

Composting is an aerobic process (although it can be applied to the residue of anaerobic digestions aimed at producing methane) carried out in both industrial and household settings. In some countries, household composting is very popular. However, it is important to note that home composting is not simply a scaled-down version of the industrial process; they are two different methods. Household composting promotes personal responsibility in waste management and streamlines the treatment of portions that otherwise would reach centralized management facilities. Nevertheless, the conditions for the process, such as temperature, humidity, and aeration, are challenging to control in home devices and differ substantially from those maintained in industrial facilities. In the latter, compost piles are consistently aerated, humidity is controlled, and temperatures of up to 65 °C are reached. Such conditions support the growth of thermophilic microorganisms and maintain a high biological diversity. As a result, decomposition times are significantly reduced in comparison to home composting.

Bioplastics are not generally suitable for home composting. Industrial compostability is regulated by standards such as EN 13432 (packaging) and EN 14995 (general). Various entities like DIN Certco or TÜV-Austria certify the compostability of materials, and there is even a recent European standard (July, 2023) certification materials for home composting systems (EN 17427: Packaging – Requirements and test scheme for carrier bags suitable for treatment in well-managed home composting installations.). The most significant difference is that while home composting systems operate at room temperature (typically 25 °C), the industrial ones are certified at 58 °C. This is why specific certifications like TÜV OK Compost Home exist.

Industrial and home composting and BioCom materials

Domestic composting works reasonably well with lightweight bags. These are films made from thermoplastic starch and bioplastics such as poly(lactic acid), which degrade in industrial composters over a period ranging from a few weeks to several months, depending on the conditions and technology used (compliance with the EN 13432 standard requires at least 90% degradation within 6 months). In household piles, the process is much slower and can take a year or more, which might lead to suspicions of fraudulent certification, though this is not necessarily the case. Recent research in this regard can be found in the original publication, and its media coverage is documented in the review published in The Age of Extinction section of The Guardian newspaper.

It was previously mentioned that bioplastics do not simply disappear in the environment, as demonstrated a few years ago by an article showing how a biodegradable bag could remain functional even after years submerged in the sea. This is not surprising but rather a consequence of the fact that compostable plastics are precisely that: compostable. If they were so fragile as to decompose quickly in the environment, especially under low-temperature and low-oxygen conditions like those of the marine environment, they would be impractical. The following photo shows pellets of PHB, polyhydroxybutyrate (PHB), or poly(hydroxybutyric acid). It can be observed that after five years submerged, they have barely undergone any changes, as expected.

Pellets of virgin polyhydroxybutyrate (PHB) and after 5 years submerged in water at room temperature (they are not the same specimens, although they are from the same batch)

What has been said so far makes it clear that bioplastics are not harmless materials that can be abandoned in the environment with the hope that they will disappear on their own. (A special case is agricultural mulch films that can be left in the soil after the harvest period; this topic will be addressed in a later post in this blog.) Similar to conventional plastics, bioplastics are materials designed for specific uses and can help solve certain problems, such as the carbon footprint associated with the use of fossil resources. However, they will not by themselves solve the issue of plastic dispersion in the environment, which is fundamentally a waste management problem, not a material science problem.

What is a bioplastic?

Most of the plastics we currently use come from fossil sources. In other words, the carbon they contain comes from petroleum-derived products. As a result, their degradation releases into the environment carbon previously trapped underground. The steady increase in carbon dioxide concentration in the atmosphere since the Industrial Revolution is an undeniable fact. Its potentially serious effects on the climate have prompted the search for ways to reduce the carbon footprint of our industrial activities, and one of these is the replacement of conventional plastics with renewable alternatives.

The industry has developed for this purpose a range of materials collectively known as bioplastics. The idea is that using raw materials from plant sources, the balance would be neutral, as the emitted carbon would have been previously captured (and recently, not over geological timescales) by plants. It’s important to highlight that the carbon footprint of a product is not solely that of its raw material, but also includes processing, storage, and transportation phases that might not be decarbonized: the calculation method is defined by the EN-ISO 14067 standard (Carbon footprint of products – Requirements and guidelines for quantification).

However, when seeking a concrete definition of bioplastics, things become complicated. According to European Bioplastics, a European association of bioplastics manufacturers that brings together many leading companies in the sector, bioplastics are a family of materials that includes products that are bio-based, biodegradable, or both. In fact, bioplastics can be produced from renewable sources like cellulose, they can be synthesized from monomers produced through biotechnological processes, or they can be biodegradable plastics derived from fossil sources. In other words, bioplastics are loosely defined materials, and under this heading, a wide variety of typologies can be found. Let’s explore the issue more in detail.

First, a material is considered biobased when it is produced from biomass, meaning it is obtained from plants, algae, microorganisms, or any other biological source. The criterion is reasonably clear, although most definitions like the one provided by the cited European Commission or the United States Environmental Protection Agency include partially biobased materials in the bio-based category.

As for biodegradability, there are standardized norms for quantifying it in different environments, such as EN ISO 19679 related to the interface between marine water and sediments, or EN ISO 14851 which determines the aerobic biodegradability of plastic materials in aqueous environments. However, biodegradability is not an on-off concept. All organic materials are potentially biodegradable, although in some cases, the process might take a long time. A key issue is that a biodegradable product is not designed to be discarded into the environment, as highlighted a few years ago in a famous article by Richard Thompson (the same person who coined the term ‘microplastic’), which demonstrated how a biodegradable bag was capable of surviving in the sea for years.

That’s why instead of biodegradability, it’s preferable to use the term compostability, which refers to biodegradability under industrial composting conditions and is quantified as indicated in the standard EN ISO 14855-1 (determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions). Achieving proper composting is not a straightforward task, and degrading bioplastics might require a significant amount of time even in well-designed composting facilities.

All plastics, not only bioplastics, can be classified based on their compostability (compostable/non-compostable) or their material carbon footprint (fossil-based/bio-based), as shown in the Figure. It’s important to emphasize that this classification refers to the polymer that forms the plastic, not to the additives the plastic may incorporate (sometimes in proportions as high as 40% by weight). Materials that are both compostable and bio-based are referred to as BioCom, which some authors consider to be the true bioplastics.

Classification of plastic polymers based on their carbon footprint and compostability: TPS: thermoplastic starch, PLA: polylactic Acid, PBAT: poly(butylene adipate-co-terephthalate), PCL: polycaprolactone, PE: polyethylene, PP: polypropylene, PET: polyethylene Terephthalate, PVC: polyvinyl chloride

The figure includes some compostable (biodegradable) plastics of fossil origin, as it is possible to synthesize compostable materials from petroleum. This is the case for poly(butylene adipate-co-terephthalate) (PBAT) or polycaprolactone (PCL). It is also possible to synthesize non-biodegradable or traditional polymers like polyethylene (PE) from renewable sources, using conventional petrochemical synthesis routes.

It’s important not to confuse biodegradable plastics with oxo-degradable or oxo-plastics, which are conventional plastics that included additives to accelerate their fragmentation through heat or exposure to sunlight. These materials were true sources of microplastics and were banned in Europe under Directive (EU) 2019/904 on reducing the impact of certain plastic products on the environment.

In essence, compostable bioplastics (BioCom) contribute to decarbonizing the life cycle of plastic because regardless of their end-of-life destination, the materials used in their manufacturing do not come from fossil sources. If properly processed at the end of their life, they don’t generate the secondary microplastics that contaminate compost.

However, it’s important to take into account that:

1. Plastics consist not only of the polymer, as it also contains additives; besides, its carbon footprint can also stem from manufacturing and distribution processes.

2. The management of bioplastics at the end of their life isn’t always clear, as they might be recyclable (sharing bin with packaging), compostable (biowaste bin), or both. (Furthermore, distinguishing a bioplastic from a conventional plastic isn’t always easy.)

3. Producing plastic from plant sources can divert arable land from food production.

4. Biodegradable plastics are also less stable than conventional ones, which can result in toxicity due to faster release of additives or the emission of nanoplastics.

Plastic waste, circularity, and recycling

The global economic order is built upon the exploitation of numerous non-renewable resources. The unsustainability of this model in the long term is increasingly hard to ignore and is evident not only in the depletion of raw materials but also in numerous negative impacts on the environment. In 1972, an essential book on this topic was published. It is called ‘The Limits to Growth’, written by various scientists from the Massachusetts Institute of Technology at the request of the Club of Rome. The authors used computer models to predict an ecological crisis that would occur during the 21st century due to resource depletion and pollution. The 2012 version, ‘Les limites à la croissance (dans un monde fini)’, updated and revised through the concept of ecological footprint, essentially agrees with the earlier version.

In this context, there arises the need to replace traditional, non-linear flows with circular flows that minimize resource extraction and waste generation. This is known as a circular economy, which takes inspiration from biological systems and is scientifically grounded in the concept of ‘Industrial Ecology‘, formalized by Thomas E. Graedel in 1996. Nature produces no waste. Accordingly, and from the point of view of Industrial Ecology, waste is the consequence of imperfect production processes that need to be overcome in favour of a circular flow of materials. It is very challenging -probably impossible- for an industrial society to operate in a fully circular manner, but the reality is that the current production flow is highly non-circular, leaving ample room for improvement.

According to Plastics Europe, global plastic production reached 390.7 million metric tons (Mt) in 2021 (excluding polymers not used in the conversion of plastic parts and products such as textile fibers, adhesives, or coatings). In 2020, the amount of plastic waste recovered in the EU 27+3 (EU plus UK, Norway, and Switzerland) amounted to 29.5 Mt, which is slightly over half of the plastic production in these countries. Approximately one-third of the collected plastic waste is recycled (although only half, 5.5 Mt, is incorporated into new products). A quarter of those 29.5 Mt goes to landfills (23.4%, 36% in Spain), and the rest is incinerated. Across the countries, the plastic cycle is even further from being circular. According to the OECD, plastic waste increased from 156 Mt in 2000 to 353 Mt in 2019. Out of this, 55 Mt could be collected for recycling, and only 33 Mt could be reintroduced into the production cycle (9.3%).

Plastic cycle in global figures from OECD (in brackets figures form Plastics Europe) for 2019 and figures for the UE 27+3 in 2021, last year with data available. Sources: OECD (2022), Global Plastics Outlook: Economic Drivers, Environmental Impacts and Policy Options, OECD Publishing, Paris, https://doi.org/10.1787/de747aef-en and Plastics Europe. Plastics—The Facts 2022: An Analysis of European Plastics Production, Demand and Waste Data. PlasticsEurope; Association of Plastics Manufacturers, Brussels, 2022, https://plasticseurope.org/knowledge-hub/plastics-the-facts-2022/

In this context, the Directive 850/2018 amending Waste Directive 1999/31/EC established that Member States must take necessary measures to ensure that by 2035 the amount (weight) of municipal waste deposited in landfills is reduced to 10%, at least, with respect to the total amount of municipal waste generated. This text and the local regulations transposing it establish recycling targets and the need to set up separate collection of domestic-origin textiles and biowaste. The key to the expansion of reuse and recycling lies in Extended Producer Responsibility schemes that embody the idea that producers and distributors are responsible for the waste generated by their products throughout their entire lifecycle. Depending on the type of waste, different schemes of that type exist, including packaging, tyres, and electronic devices among others.

Plastic has not been mentioned so far, as current recycling systems do not always have specific provisions for it. In Spain Ecoembes established a recycling system for packaging made from any material (including wood) and elements such as caps or closures, but not non-packaging plastics. According to Ecoembes, in 2021, they processed 1.6 million tons of packaging waste that representing 84% of domestic packaging put on the market, although the figure is controversial and has been lowered by independent estimations to around 30%. Small containers, dark-coloured items, multi-layered (Tetra Brik) containers are not recycled, or their recycling is very limited. All these materials end up in landfills or, in the best case, are incinerated. Plastic kitchen utensils, toys, pens, coffee capsules, and, in general, any plastic material that is not packaging or a part of it, are currently outside recycling schemes. It’s important to highlight that many objects are made from multiple materials and, therefore, are very difficult to recycle. A typical example of composite material is diapers, with outer and inner layers of polyethylene and polypropylene, respectively, and polyacrylate as the absorbent material. Limiting to packaging is indeed a weakness, although it’s also important to acknowledge that packaging constitute a quantitatively significant portion of plastic waste: 39.1% of the plastic demand in EU 27+3 is devoted to packaging production.

Another important aspect to be highlighted is that plastic recycling is not unlimited. After a few cycles, the polymer loses quality due to degradation during use or reprocessing, or due to the presence of additives from previous uses. It is possible to use degraded plastic to manufacture products with lower requirements, but sooner or later, it will have to be discarded. It’s a well-known fact that polyethylene terephthalate can be recycled into textiles (polyester): five large bottles can produce a t-shirt. Recycling materials for textiles is a positive step, although it’s not an absolute solution. Garments incorporating recycled polyester still release microplastic fibers, and furthermore, their incorporation into textiles disrupts circularity in the packaging sector, given the nearly non-existent recyclability of synthetic textiles.

The recycling of plastics is typically mechanical. It involves shredding the material to produce recycled pellets used by compounders. When this is not feasible for technical reasons, chemical recycling can still be used, which involves techniques such as thermal cracking or hydrolysis to convert the macromolecules that constitute the plastic into products suitable for new uses. The new uses could involve the production of new polymers or not. For example, Plastic Energy operates two plants in Almería and Seville with the capacity to produce 10,000 tons/year of pyrolysis oil from agricultural plastics, which can be used as fuel or in catalytic cracking units to produce plastic monomers. Gasification to obtain synthesis gas (a mixture of carbon monoxide and hydrogen) is another form of chemical recycling. In Spain, Repsol, Enerkem, and Agbar have announced the construction of a gasification plant for non-recyclable municipal solid waste (including plastics) to produce methanol. Finally, energy recovery allows for harnessing the energy contained in the chemical bonds of waste. This practice is less common in Spain than in other countries (20% compared to 42% of plastics recovered in EU 27+3), but it is always preferable to landfill plastics that cannot be treated otherwise.

Certainly, there are materials easier to recycle than others. Polyethylene terephthalate (beverage containers) or high-density polyethylene (common in numerous plastic objects) are relatively straightforward to recycle. Others like polyvinyl chloride (water pipes, synthetic leather) or polystyrene (insulation, packaging material) present greater complexity. Bags and films (low-density polyethylene) are difficult to recycle because they tend to produce jams. Composite materials are generally not recyclable. Hence the need to manufacture single-material products, especially for high-demand items like packaging. Reducing the need for virgin material, extending the lifespan of objects (including textiles), investing in selective collection systems, limiting single-use plastic items, and using rational fiscal policies with fees for suboptimal waste management (Pay-as-you-throw) are some of the main tools available to enhance circularity in the plastic market.

Synthetic, artificial, and natural fibers

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.

Fleece lining and polyester fibre taken out from it

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.

Synthetic, semi-synthetic, natural and artificial polymers

The concept of microplastics is reasonably well established. As mentioned in other posts, microplastics are plastic particles whose major dimension falls within the range of 1 to less than 5000 microns (5 mm). However, it is important to provide some clarifications regarding what constitutes a plastic for regulatory and environmental purposes, as the term ‘plastic’ corresponds more to common language than to scientific terminology. As indicated later, a plastic is a subclass of polymeric materials. A polymer (Article 3.5 of the REACH Regulation and ECHA Guidance for Monomers and Polymers) is a substance composed of at least 50% by weight of molecules formed by the covalent bonding of (at least three) constituent units called monomers, that may also include a variety of simple molecules acting as plasticizers, stabilizers, or other functions.

Polymers can be thermoplastics, thermosets, and elastomers. Thermoplastics (including all synthetic fibers) can be melted and indefinitely moulded without suffering substantial degradation- Thermosetting polymers have their molecules linked in a three-dimensional network and cannot be melted. Elastomers, like thermosets, have their molecules crosslinked, as in vulcanized rubber, but instead of being rigid, they exhibit elastic behaviour without undergoing permanent deformations. Typical examples of thermoplastics are polyolefins (polyethylene or polypropylene), polystyrene, or PVC, while epoxy resins and polyurethanes are thermosets. Some old classifications of polymers only include thermoplastics and thermosets, excluding elastomers, but the development of thermoplastic elastomers, especially since the 1970s, has blurred the boundaries between these materials and suggests their unified treatment.

Polymer types: thermoplastics, elastomers, and thermosets

Plastic materials, regardless of its shape and in the context of environmental pollution and related fields, must be water insoluble. (This excludes some polymers like povidone or polyethylene glycol.) This limitation can be found in the restriction proposal developed in 2020 by the European Chemicals Agency (ECHA) concerning intentionally added microplastics in products placed on the community market. The report was jointly prepared by the Committee for Risk Assessment (RAC) and the Committee for Socio-economic Analysis (SEAC) at the request of the European Commission in order to adopt the measures required by the REACH Regulation (Annex XV). In addition to clarifications about particle dimensions, the report indicates that the regulation excludes natural polymers that have not been chemically modified, biodegradable polymers (according to specified criteria in Table 22 of the background document), and those with solubility > 2 g/L. Natural polymers are excluded from regulation as defined in the REACH Regulation, Article 3.40, provided they have not undergone a modification of their original structure (though certain chemical or physical treatments are allowed, for instance, to remove unwanted substances).

There is a variety of polymeric materials that, despite originating from natural polymers, cannot be considered as such because they have undergone chemical modifications. The most well-known example of this family of semi-synthetic polymers is regenerated cellulose. This material is obtained from cellulose fibres (such as cotton), which are treated with carbon disulphide in a basic medium to form cellulose xanthate. Cellulose xanthate is then mechanically processed, and cellulose subsequently reconstituted in an acidic medium (while there are other methods to regenerate cellulose, the one mentioned is the most commonly used in commercial applications). Rayon and cellophane belong to this group of materials. Rayon, referred to as viscose in Europe, is the most common semi-synthetic polymer. Its silky shine made it very popular as a silk substitute since the late 19th century. (Nylon is another classic example of synthetic silk substitute, although nowadays, polyester is used for that purpose.) Once cellulose is regenerated, the resulting material is difficult to distinguish from cotton or other cellulosic fibres using spectroscopic techniques. Vulcanized natural rubber is another example of a semi-synthetic polymer, although it has long been replaced by fully synthetic elastomers. Another notable group consists of cellulose nitrates, which include celluloid and gun cotton.

The typology of polymeric materials thus encompasses three types of substances: (1) natural polymers, (2) artificial materials based on natural polymers that have undergone chemical transformations or industrial processing, and (3) purely synthetic polymers. In the context of environmental sciences, the term ‘plastic’ exclusively refers to synthetic polymers, which are those in which the constituent monomers have been obtained through chemical synthesis (from materials of any origin, fossil, or non-fossil).

Types of polymeric materials based on their chemical composition

The previous classification includes a dual typology of artificial materials: semi-synthetic polymers (such as rayon) and industrially processed (but not chemically modified or treated) natural polymers. This is because natural polymers are not marketed in their raw state as obtained from nature. Instead they reach our hands after undergoing various industrial processes that generally involve the incorporation of a wide range of chemical additives. Without straying from the textile industry, the list of chemical substances involved in fabric manufacturing processes is quite extensive. It includes bleaching agents, softeners, lubricants, antistatics, emulsifiers, coagulants, defoamers, dyes, and biocides, among others. Many of them are entirely synthetic compounds that become incorporated to different degrees into the fabric, either incidentally or intentionally. Some dyes are toxic, such as those based on quaternary ammonium compounds which, being cationic, can interact with the negatively charged cell membranes. Azo dyes, common in many fabrics and generally considered non-toxic, are also hazardous as some of their metabolization and degradation products do exhibit toxicity to various organisms.

In essence, both plastics themselves and semi-synthetic polymers, along with industrially processed natural materials (thereby transformed into artificial materials), should be regarded as anthropogenic pollutants, either due to their inherent properties or to the substances accompanying them as additives or remnants of the reagents used in their production. Their effect to the natural environment is still poorly understood, but it is certain that they reveal an impact of human activity on the natural environment.

Size matters, but it’s not the only thing that matters

Size defines a microplastic. As mentioned earlier, a solid particle is considered a microplastic when its main component is a synthetic organic polymer, and its size, measured as its major dimension, falls between 1 µm and < 5 mm. However, size is not the only important information about microplastic particles. Along with size, it’s common to include descriptors that help understand the material’s origin. Industrial granules, packaging foams, or remnants of fishing nets correspond to very different sources of emission, and their identification is relevant for the purpose of combating this type of pollution.

Since the beginning of the research on microplastics, several classifications based on shape or typology have been proposed. Hidalgo-Ruz and coworkers, in a well-known review article, mention the following types of microplastics: fragments, pellets (granules), filaments, films, foams, granules, and Styrofoam (a commercial name for extruded polystyrene foam). In another common reference, Lusher and her team distinguish fragments, fibers, beads, foams, and pellets. Finally, the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) in their 2019 Report No. 99, while acknowledging the difficulty of standardizing the morphological classification of microplastics, proposes five categories:

1. Fragments: Irregular particles originated from the fragmentation of larger ones.

2. Foams: Approximately spherical and easily deformable particles.

3. Films: Flat and flexible particles.

4. Lines (or filaments): Particles with substantially greater length than width (high aspect ratio).

5. Pellets: Granular particles that are hard and have a smooth surface.

The subjectivity of that classification is evident, and even though GESAMP suggests creating subdivisions, such as distinguishing lines or filaments (from fishing nets, for example) from textile fibers, the separation between categories is blurred. For instance, the length-to-width ratio that distinguishes a filament from a fragment is not specified. The flexibility required for a particle to be classified as foam rather than a fragment is also not mentioned.

The shape of particles can be quantitatively described using various descriptors. The clearest one is the minimum aspect ratio (the ratio of length to diameter) required for a fibre or filament. It’s common to use a minimum value of 3 for the length/diameter ratio of fibers, which is a value inherited from asbestos legislation: “The term respirable asbestos fibres denotes asbestos fibres with a diameter of less than three micrometres and with a length-to-diameter ratio greater than 3 to 1” (International Labour Organization, C162 – Asbestos Convention, 1986).

Particle science employs techniques to accurately quantify a particle’s shape. X-ray microtomography, for instance, enables the determination of the three orthogonal dimensions of a particle: L (major dimension), I (intermediate dimension or the greatest dimension perpendicular to L), and S (dimension perpendicular to both L and I). To ensure this attribution is unambiguous, some additional clarifications are necessary, such as requiring L, I, and S to be the dimensions of the smallest orthogonal parallelepiped that encloses the particle, as shown in the following figure.

Microplastic defined based on the dimensions of the smallest orthogonal parallelepiped that encloses the particle

The shape description based on L, I, and S can be made dimensionless by defining three parameters: roundness, S/L; planarity, (I-S)/L; and elongation, (L-I)/L. These three parameters sum up to one, and they can be visually represented on a ternary diagram. In this diagram, spherical shapes, which exhibit greater roundness, approach the upper vertex. Flat shapes, with higher planarity, move toward the lower-left vertex. Lastly, fibers, characterized by greater elongation, converge at the lower-right vertex as shown in the figure below. (Plastic number 5 is the one shown in the preceding figure.)

Basic morphologies of microplastics in a ternary diagram of roundness-planarity-elongation, along with examples of actual plastics from marine origin

A classification like this is relevant because the environmental distribution of plastic particles depends on size (measured as the major dimension) and shape, and both factors determine their behaviour in a fluid medium, whether it’s water or air. Specifically, the shape of particles strongly influences their sedimentation rate. A fibre settles at a much slower rate than a rounded particle of equal mass and volume. This explains the high mobility of fibers and their prevalence compared to fragments as we move away from urban centres. The unique characteristics of synthetic fibers will be discussed later in this blog. For more information on the topics covered here, you can refer to this article, available in the author’s version.

What is and what is not a microplastic

If we ask a random person what a microplastic is, they might respond that it’s something that can only be seen with a microscope. The answer is both yes and no, and this may be surprising, because in this neologism, science and common sense don’t entirely align. Let’s start with the definition. The word ‘microplastic’ was set to refer to the small plastic fragments that have become one of the main threats to the environment and human health. The Merriam Webster dictionary lists the word in an imprecise manner: ‘a very small piece of plastic especially when occurring as an environmental pollutant’. Despite the vagueness of the definition, it includes two important elements that define microplastics: size and their nature as anthropogenic pollutants. In what follows, I will explain how size defines microplastics in a precise way.

The observations of Dr. Kara Lavender Law’s group precisely documented the accumulation of small plastic debris in the North Atlantic Gyre. The results of 22 years of studies (from 1986 to 2008) on samples collected using trawl nets were published in Science in 2010, enabling the quantification of the number of particles and the mass of floating plastic in one of its main accumulation zones. In this work, nets with a mesh size of 335 microns were used for practical reasons, as finer nets clogged up quickly. The published data indicated that 12% of the plastic particles were bigger than 10 mm in their larger dimension. The term ‘microplastic’ existed at the time this article was published (in fact, it’s used three times), although it did not yet have a precise definition.

The term ‘microplastic’ was coined by Richard Thompson and collaborators in another celebrated (and brief) article that appeared in Science in 2004 as an acronym for ‘MICROscopic PLASTIC.’ With this neologism, the authors referred to small granular or fibrous fragments with an approximate dimension of around 20 microns that were being found in sampling campaigns of beaches and seas in the United Kingdom. Much smaller, therefore, than those that were being detected floating is floating debris in the oceans.

The first precise definition of microplastics came from the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP). In their Report Number 90, issued in 2015, they defined microplastics as ‘particles in the size range of 1 nm to < 5 mm.’ The reason for the upper limit of 5 mm, which is somewhat inconsistent with the use of the prefix ‘micro,’ is due to the need to ensure continuity with the scientific data collected up to that point, mostly using plankton nets with mesh sizes in the hundreds of microns range. The fact that 5 mm refers to the ‘major dimension,’ which is a non-trivial detail, was not explicitly stated until 2019 in GESAMP’s Report Number 99: ‘Guidelines for the monitoring and assessment of plastic litter and microplastics in the ocean’.

The image shows several plastic fragments with dimensions larger than a few millimetres and a filament that, despite its reduced diameter, does not fit the definition of microplastic due to its length being over 5 mm. The issue posed by objects with high aspect ratio (length divided by width) is complex and will be addressed in another post. For comparison, a human hair is shown, with an average thickness around 70-80 microns. Plastics equal or larger than 5 mm are referred to as mesoplastics (5-25 mm), macroplastics (25 mm-1 m), or megaplastics (> 1 m). This classification comes from the aforementioned GESAMP Report Number 90 and should be understood in reference to the major dimension, although it wasn’t specified as such at that time. Plastics smaller than 1 micron, approximately the size of a cell of the bacterium Escherichia coli, are termed nanoplastics. The definition of nanoplastic warrants a more detailed treatment.

Lower and upper limits for the definition of microplastics based on their size, understood as their larger dimension

At the origin of plastic waste research, there was no lower limit for the size of microplastics. In GESAMP’s Report Number 90, it was stated that ‘microplastics extend to nanometric scales.’ Recently, the RAC (Committee for Risk Assessment) and SEAC (Committee for Socio-Economic Analysis) committees of the European Chemicals Agency (ECHA) recommended a lower size limit of 100 nm for the purpose of implementing restrictions on intentionally produced microplastics, which are the so-called ‘primary microplastics’. After considerable discussion, the Committees did not establish a lower limit due to practical reasons, although they acknowledged that there are commercial products with plastic additives < 100 nm. Therefore, the 100 nm limit only applies to the restrictions imposed on manufacturers by the REACH Regulation, specifically targeting substances placed on the EU market, and is not generally suitable for environmental studies.

Secondary microplastics are those produced by the degradation of larger plastics and not intentionally manufactured at that size. A lower size limit for secondary microplastics, and in general for microplastics in environmental studies is generally established as 1 µm. Below this limit, plastics are commonly referred to as ‘nanoplastics’. As in the case of microplastics, the nomenclature doesn’t align well with the use of the prefix ‘nano’, which in the case of synthetic nanoparticles are those with at least one dimension < 100 nm. However, the 1 µm boundary suits the characteristics and behaviour of these small plastic particles in the environment. In the first of their two articles on the subject, Julian Gigault and his team proposed that unintentionally produced particles (secondary plastics) with colloidal behaviour and a size range between 1 nm and 1 µm should be termed nanoplastics. (Once again, the lower limit is relevant: 1 nm is the size of a sucrose molecule, and in that range, the concept of ‘particle’ ceases to make sense.) Precisely among the distinctive characteristics of nanoplastics, the most relevant is their ability to remain in colloidal suspension in water and to undergo Brownian motion in the air. The micrometre roughly marks the difference between colloidal/Brownian behaviour and that of particles that settle or deposit due to gravity.

In summary, microplastics encompass a vast range of sizes, spanning from 1 µm, equivalent to the size of a bacterium, to < 5 mm, comparable to that of a garden ant. This range is as large as the difference between an ant and a blue whale. It is important to note that the limits of 1 µm and 5 mm are operational and do not denote absolute distinctions.

Ocean gyres and plastic “islands”

It’s easy to come across information that refers to the “plastic islands” supposedly accumulating in the world’s oceans. Even in seemingly reputable sources, images like the one below frequently appear. This particular one is accompanied by the caption “300-Mile Swim Through The Great Pacific Garbage Patch Will Collect Data On Plastic Pollution” and it appears to depict a buildup of garbage in one of the seven plastic islands located in the five major gyres, which I will mention below, along with additional accumulations in the Sargasso and Barents Seas. There are many other examples of striking accumulations of plastic presented as images from the ocean gyres. However, those “plastic islands” don’t actually exist. They are a manipulation assembled upon a true reality, which is the accumulation of plastic in the environment, particularly in the oceans. Let’s explore what’s accurate and what causes plastic fragments to float in our seas.

Press image illustrating one of the alleged “super islands” of plastic floating in the world’s seas

The first data on the presence of plastic in the sea dates back to 1972 when Carpenter and Smith reported the presence of small plastic particles in the Sargasso Sea, collected during surface samplings using plankton nets. The surface density they calculated was 3500 particles per square kilometre, equivalent to one particle per 280 square metres (less than 1 mg per square metre). The majority of the particles were described as pellets (industrial material) ranging from 2.5 to 5 mm in size. This is the type of material often seen in areas near plastic production facilities, such as the beaches of Tarragona, Spain.

This finding (like others) went relatively unnoticed until solid evidences were presented regarding the accumulation of plastic in the ocean gyres. Ocean gyres are currents that follow a circular path due to Earth’s movement. There are five major ocean gyres, one in the Indian Ocean and two in each the Atlantic and Pacific Oceans, rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. In 2010, Kara Lavender Law and her team published the results of twenty-two years of studies on samples collected in the subtropical North Atlantic gyre. Their findings demonstrated that in the area of greatest accumulation (from 29° to 31° N), the number of floating plastic particles was about 20,000 per square kilometre (this is one per every 50 m²).

Law and her team collected particles larger than 335 microns (a micron being one thousandth of a millimetre) and mostly smaller than 10 mm. The estimated total mass was 1,100 tons, distributed over the approximately two million square kilometres of the gyre. It’s noteworthy that as of 2010, the size of microplastics hadn’t been defined yet, so the particles counted by Law and her team included both microplastics (between one micron and 5 mm) and mesoplastics (from 5 to 25 mm). The term “microplastic” was coined in 2004 by Richard Thompson from the University of Plymouth, as an acronym for “microscopic plastic”, although the upper size limit of 5 mm wasn’t established until 2015. Though the best documented, Law’s discovery wasn’t the only one. A few years earlier, in 2001, Charles Moore and his team published data confirming the presence of plastic in the subtropical North Pacific gyre, with maximum concentrations of 334,271 particles/km² (one particle every 3 m²).

As seen, the density of floating particles, less than one per square meter of surface area, and their small size, most of them smaller than a millimetre, make their detection difficult even when sailing through them. The image below is an actual photograph taken at the centre of the subtropical North Pacific gyre: The real Great Pacific Garbage Patch. Photo by Miriam Goldstein, 2010 EX1006 cruise. It’s nothing like the first picture, but that doesn’t make it any less of a significant environmental pollution issue.

Actual photograph of the “plastic island” in the subtropical North Pacific gyre

It’s a pity that reality spoils a terrifying fiction, but distorting facts can only contribute to not taking seriously the threat posed by plastic accumulation in the environment. Plastic pollution is mainly a result of the mismanagement of our waste. (There are other causes like the aforementioned pellet leaks and other hardly avoidable factors like the wear and tear of materials during use, such as in the case of tires or synthetic textiles.) Furthermore, what we see floating in the sea is exactly that, floating plastic: most plastic has a density higher than that of water and doesn’t float, but that doesn’t mean it ceases to exist.

The OECD recently estimated that globally, less than ten percent of plastic is properly recycled. The rest ends up in landfills or is incinerated at best; at worst, it’s scattered in the environment. Most plastics consist of a synthetic polymer with additives that give rise to a material considerably resistant to degradation, making it a persistent contaminant when dispersed in the environment, capable of lasting for years or even centuries. To date, around ten billion tons of synthetic polymers have been produced, and it is estimated (as per the same OECD report) that around 140 million tons of plastic have already accumulated in aquatic ecosystems, three-quarters of which are in rivers and the rest in oceans. Once in the environment, plastic releases the chemical compounds added in its formulation and breaks down into smaller and smaller pieces, the actual risks of which are still undetermined.

In conclusion, “plastic islands” do not exist, but the accumulation of plastic in the natural environment is a very real fact, primarily stemming from the mismanagement of a material that is inherently extremely useful, even irreplaceable in many applications.