G.S. Pathak, M. Hinge, D.E. Otzen, Transdisciplinary pragmatic melioration for the plastic life cycle: Why the social, natural, and technical sciences should prioritize reducing harm, Sci Total Environ 895 (2023) 165154. PDF version
Towards a policy of pragmatic melioration for plastics use: why the social, natural, and technical sciences should collaborate to reduce harm
Gauri S. Pathak,1,* Mogens Hinge,2,* and Daniel E. Otzen3,*
1 Department of Global Studies, Aarhus University, Jens Chr. Skous Vej 7, 8000 Aarhus C, Denmark
2 Department of Biological and Chemical Engineering - Process and Materials Engineering, Aarhus University, Aabogade 40, 8000 Aarhus C, Denmark
3 Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark
All authors contributed equally to the work.
Plastics underpin modern society but also threaten to choke it. Only 9% of all plastics are recycled, usually with loss of quality (“downcycling”); the rest is landfilled or dumped (79%) or incinerated (12%). Put bluntly, the “plastic age” needs a “sustainable plastic culture.” Consequently, we urgently need to develop a global and transdisciplinary approach to fully recycle plastics as well as to manage the harms across their life cycle. The past decade has witnessed an explosion in research on new technologies and interventions that purport to help solve the plastic waste challenge; however, this work has, in most cases, been carried forward within single disciplines (for example, researching novel chemical and bio-based technologies for plastic degradation, engineering processing equipment innovations, and mapping recycling behaviours). In particular, although vast progress has been made within the individual scientific fields, such work does not address the complexities of various plastic types and waste management. Meanwhile, research on the social contexts (and constraints) of plastic use and disposal is rarely in conversation with the sciences to drive innovation. In short, research on plastics typically lacks a transdisciplinary perspective. In this review, we urge the adoption of a pragmatic and transdisciplinary approach that we call pragmatic melioration, which combines the natural and technical sciences with the social sciences to focus on the mitigation of plastic harms and the maximization of their value. We first review the status of plastic recycling from these three scientific perspectives. Based on this, we advocate foundational studies to identify sources of harm and to prioritize global/local interventions aimed at those plastics and aspects of the plastic life cycle that cause maximal harm, both in terms of planetary welfare and social justice. We believe that such an approach to plastic stewardship can also be a showcase for tackling other environmental challenges.
The invention and application of plastics is one of the technological revolutions that form the basis for our consumer society. One of the attractions of plastics, when they were introduced at the beginning of the 20th century, was their durability. “Plastic is forever” was a promise, not a threat. Plastics are immensely useful because of their weight, strength, and resilience, thermal and electrical insulation, and resistance to water and gas. Consequently, they have numerous applications in daily life, ranging from packaging to extend food shelf life (for example, meat trays, fruit, and vegetable wrap) and protect goods during transport (for example, boxes and dividers) to serving as components in industrial products (for example, wind-turbine blades) or as household items (for example, bowls), to being essential in life-saving medical devices (for example, personal protective equipment, syringes, and medical tubes)1,2. Plastic items are ubiquitous and have become entangled with almost all aspects of life. However, a future with plastics has its complications.
More than 400 million tonnes of plastics are produced annually3. Packaging comprises the largest single segment (40.5%), followed by building and construction (20.4%), transportation (8.8%), and electronics (4.3%). As can be expected from this distribution, ≈50% of all produced plastics have a short usage span (less than 6 months), and the remaining have a long usage span (for example, 25–30 years in service). Thus, a conservative estimate is that ≈200 million tonnes of plastic waste is generated within a year4; additional tonnage is discarded from long-term items going out of service (for example, house renovation and demolition).
The potential human health and environmental harms caused by plastics, including micro- and nano-plastics as well as additives used to modify plastic properties, are of increasing concern5-9. Moreover, poor waste management means that an estimated 79% of all plastics ever produced end up in landfills or are directly discarded into the environment3. Rising political awareness of these challenges has resulted in a push for a binding Global Plastics Treaty, initiated by the recently (December 2022) concluded intergovernmental negotiating committee session in Uruguay10, which will be followed by a second session in Paris in May–June 202311.
The plastic “waste hierarchy” states that we should first and foremost reduce consumption. Thereafter, we should reuse plastic items as much as possible. Following that, we should aim to recycle materials from products that (inevitably) break; purify inferior plastics (for example, those containing unwanted additives or that are otherwise degraded) to recover the constituent polymers; degrade the plastics thermally, chemically, or (preferably) biologically to chemicals (for example, fuels and monomers); and, if that is not possible, recover energy through plastic waste incineration (preferably combined with carbon capture and storage to minimize greenhouse gas release). Disposing in landfills or (even worse) dumping in nature is the absolute last resort as it results in a complete loss of value and presents issues of leachate, landfill gas emissions, and space, among other things12,13. However, dumping and open burning (and in some cases landfilling or burying) is the norm in most of the world, resulting in vast amounts of plastic pollution.
The highly simplified waste hierarchy approach clearly demonstrates that an extremely broad set of research disciplines is needed to tackle the problem. These span from fundamental science (to invent new and much-needed technologies to modify plastics), to designers and engineers (to establish facilities and implement applications), economics, business, and to the legal, social (to investigate social contexts and develop tractable interventions), and pedagogical sciences (for eco-literacy campaigns). In addition to this, biologists, toxicologists, ecologists, and medical and public health experts are needed to map out the human and environmental consequences of plastic production, use, and disposal. This interplay between disciplines is summarized in Fig. 1. These disciplines will also need to work together to generate public awareness and political willingness to undertake broad-based change. No single research branch alone can solve the plastics challenge.
Figure 1. The connection between different disciplines working together towards a sustainable plastic culture. AI: Artificial Intelligence, ML: Machine Learning.
In this Perspective, we bring together the natural sciences (D.E.O), technical sciences (M.H), and social sciences (G.S.P) to highlight the need for interventions and solutions that are locally adapted to ground realities of waste collection, segregation, recycling, and management. Towards that end, we propose transdisciplinary collaboration across the natural, technical, and social sciences aimed at reducing harms in due recognition of the complex and interlocking challenges that must be met. We name this approach pragmatic melioration.
What Are Plastics?
“Plastics” is a common word covering a myriad of different materials14. As a first division, plastics can be classified as thermoplastics or thermosets15. Thermoplastics can be melted and reshaped, whereas thermosets are cross-linked (“cured”) and cannot be reshaped after curing. These two groups can be further subdivided according to their monomer or polymer components. Thermosets are thus divided into polyurethanes (PUR), epoxies, silicones, and so on. Thermoplastics include polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and so on. Plastics can also be divided into groups based on the chemistry of their repeating unit, as illustrated in Fig. 2.
Figure 2. The most prevalent types of plastic with the structures of the repeating units and examples of enzymes identified to be able to degrade them to smaller components. Numbers indicate million tonnes produced in 2016. Reproduced from16 with permission under the terms of the Creative Commons Attribution 4.0 International license.
Group I plastics have carbon–carbon (C–C) bonds in their polymer backbone, that is, PE, PP, PS, and PVC. Group II plastics contain non-carbon atoms, such as oxygen (as in the ester bonds in PET) and nitrogen (as in the amide bonds in PUR). The properties (for example, mechanical, stability, processing, visual) of pure polymers are often adjusted with additives. These additives include physical fillers (for example, sand, chalk, and so on), strength-giving fillers (for example, glass or carbon fibre), softeners or plasticizers, UV stabilizers, antistatic agents, flame retardants, and dyes and pigments, among others, depending on the application. For example, glass fibre-reinforced epoxy is used for wind-turbine blades to allow them to absorb/withstand wind forces, UV absorbers are added to automotive parts (for example, the dashboard) to withstand sunlight, construction components and furniture include flame retardants, and pigments enhance the visual appeal of lunchboxes and toys. Clearly, plastics are generally designed and optimized for a specific product and purpose. This means that the plastic waste stream is a mixture of a breath-taking number of plastic compositions.
Recycling Technologies and Innovations
Current mechanical recycling efforts typically involve opening, washing, sorting, cutting, and pelleting. Mixed plastic fractions are only recycled for low-value products (for example, pallets and traffic cones). Obtaining sufficient purity (95%+) for high-end and demanding products is a challenge for mechanical recycling17. The recyclers can meet this purity demand by processing either mono-component waste streams or by waste sorting. The dominant waste sorting technology is based on density (flotation sorting) and only removes polyolefins (a low-density fraction of mixed PE and PP), leaving a sinking fraction with the remaining plastics combined with non-plastic components such as sand, glass, and metals (for example, aluminium). Currently, the rising use of PET increases the sinking fraction at the expense of the recycled fraction. There is thus a paramount demand for technologies that use the sinking fraction. Among these, the enabling technology is plastic sorting, in particular, near infrared (NIR) sorting, which covers a plethora of technologies. The simpler versions employ single or dual wavelength light-emitting diodes and sensors; however, more advanced short-wave infrared camera technologies with higher success and efficiency are emerging18,19. The next challenge is to remove unwanted (or to pick out wanted) plastics. This is currently done by air blades and/or air nuzzles that “shoot” out the selected material to divert it from the remaining plastic waste stream. This technology is highly sensitive to waste shape, and most systems operate as flake (~10 x 10 mm) sorters. Despite encouraging successes, minimizing the number of operations required per tonne material removed still presents a challenge. More research is needed before the sorting challenge is solved and pure (95+ wt%) and ultrapure (99+ wt%) fractions can be obtained for further processing.
Part of the mechanical recycling process involves thermal reprocessing of the plastic material into pellets. As all thermal processes degrade polymers to various degrees, we still need to establish how many times a given plastic type can be recycled before it becomes mechanically inferior. Currently, mechanical recycling tends towards downcycling of plastic quality (e.g. mechanical, thermal and rheological properties) because of contaminants, additives, and/or complex plastic mixtures. Consequently, virgin plastic often needs to be added to satisfy material standards20.
Technologies that aim to extract unwanted additives and reclaim the polymers for making new products are being developed. Currently, the most promising technology is dissolution21-23. The general approach is to dissolve the polymer in an appropriate solvent and then filter off pigments, remove, for example, softeners via column absorption, and so on24-26. Subsequently, the polymer is extracted by precipitation, achieved by the addition of a non-solvent27-30. There are several obvious challenges facing this young technology, of which solvent recovery is the most pressing. In addition, dissolution is highly plastic-type sensitive; no solvent can dissolve all plastics. The technologies are still at a research level, and significant innovation is needed before they become commercially viable.
We urgently need technologies that can upcycle plastic by “resetting” it, that is, break it down to simple but high-value components that can be used afresh to build new plastics or other useful components. Degradation of plastics to their monomeric building blocks is attractive in principle but is unfortunately difficult in practice. At present, only some plastics (for example, polyoxymethylene (POM), poly(methyl methacrylate) (PMMA), PET, and some polyamides) can be degraded to monomers. We will subdivide chemical processing into pyrolysis and solvolysis. Enzymatic reconstruction, another degradation technology, involves radically different reaction conditions and will be grouped under biological degradation.
Pyrolysis is oxygen-free (anaerobic) thermal degradation of plastics. Pyrolysis shows promise for polyolefins and for yielding naphtha (liquid hydrocarbons) that can be processed in the petrochemical industry to fuels31,32. In addition, some polymers thermally degrade back to their constitutive monomers, directly providing monomers for repolymerization: polyoxymethylene (POM) with almost 100% yield to formaldehyde33, poly(methyl methacrylate) (PMMA) with 95% yield to methyl methacrylate32, and PS with ≈50% yield to styrene32,33. On the other hand, PET, upon pyrolysis, undergoes a cyclization and generates vast amount of char34, blocking process equipment. This process is at an industrial scale in several countries, but it is sensitive to input material and demands 80–95% pure waste streams for useful yields. It thus presents the same sorting and purification challenges as mechanical recycling. In addition, the process is energy consuming and the product typically needs post-purification prior to use. Intense research efforts are ongoing to address these challenges.
Solvolysis uses a solvent (invariably water) as reactant or media in the polymer degradation. Research is focused on either chemical degradation (breaking ester or amide bonds) or on chemically cracking the mixed plastic fraction into fuels (hydrothermal liquefaction; HTL) via thermal hydrolysis at elevated pressures. HTL degrades the plastics in sub- or super-critical water into naphtha and/or higher molecular compounds (waxes). This approach generates more fuel than pyrolysis because of free-radical chain scissions of, for example, polyolefins, while taking place under milder reaction conditions35-37. Solvolysis has also proven valuable in the depolymerization of PET into the monomers terephthalic acid and ethylene glycol, along with different lengths of oligomers38-40. It is envisioned that these monomers can be repolymerized into pristine PET. Polycarbonate (PC) studies have shown that bisphenol-A, which is the building block for new PC, epoxy, and urethane monomers, can also be obtained41-43.
Although promising, more research is needed in the depolymerization of a broader span of polymers and in a process that is less sensitive to plastic purity. HTL, while less sensitive to purity, is limited by operation and reactor costs that are challenged by very low fuel and monomer prices. Finally, HTL does not recycle plastic waste back into mono-, oligomers, or plastics. Therefore, it should be considered a dramatic downcycling, only preferable to incineration for energy and heat recovery.
Chemical resetting is sometimes challenged by its use of corrosive and toxic reagents along with very energy-demanding reaction conditions which, with few exceptions, are environmentally and energetically unsustainable44. Biological solutions are an alternative because of their mild (that is, low energy demanding) operating conditions and the enormous possibilities for improvement through engineering. A priori one would not expect biological solutions for plastic degradation to be readily available. The vast majority (>99%) of all human-made plastics are artificial compounds made by the chemical processing of fossil fuels, whose biological origins are hundreds of millions of years in the past and which have subsequently undergone a series of long and slow chemical–geological transmutations. Our ecosystems have not had enough time to develop tools to deal with plastics as they would deal with biological materials; there is no ready-made metabolic system in place to degrade plastics to smaller components, which can be recycled in other contexts. Yet our planet’s ecosystems are adaptable and versatile. There are encouraging indications that many, if not all, plastics are susceptible to biodegradation, both by microorganisms and by individual enzymes obtained from them. However, there is no one-bug-fits-all solution, as plastic degradability varies with plastic types.
Group I plastics with C–C bonds are truly alien to biology and lack obvious points of attack by normal enzymes. Before they can be dismantled to smaller pieces, they have to be made more “approachable” by oxidation. This introduces oxygen-rich chemical groups, which can then be recognized by hydrolytic enzymes and used as attack points for cleavage. Oxidation can occur either by abiotic means (typically photo-oxidation after long exposure to sunlight and air) or oxidative enzymes, such as laccases or other so-called oxidoreductases. These enzymes require helper molecules or mediators in their activity, which poses an additional challenge for efficient degradation. Overall, group I plastics present the biggest hurdle for sustainable plastic recycling. It remains to be seen whether group I plastics should be pre-treated by photo-oxidation or whether optimized oxidoreductases can do this in a competitive fashion, leaving them open to subsequent cleavage by other enzymes. There are numerous examples of microorganisms (bacteria or fungi, for example, white rot fungi which can attack tough hydrophobic polymers such as lignins in wood45) and invertebrates (particularly moth larvae such as the wax worm46) able to, for example, remove plastics from surfaces and create holes in films. While it may seem appealing to use microbes or larvae as “living factories” for plastic degradation, this approach has significant drawbacks. Plastics do not lead to growth and increase in biomass of larvae unless supplemented with more ready sources of nutrients such as starch or cellulose. It is also unclear if larvae can metabolize plastics on their own or need help from bacteria present in their gut (the microbiome); in addition, we have very limited knowledge of the actual enzymes that carry out the degradation. Plastic degradation products (for example, compounds from PVC) can be toxic and thus stunt biological activity; furthermore, larvae need to be maintained in insect cultures. Often, the final breakdown of plastic fragments requires the uptake of plastic inside the cells for intracellular conversion steps, and this can lead to bottlenecks that limit turnover. Finally, the production of large amounts of microplastics can physically compromise growth. A preferable scenario is to reconstruct plastic degradation as a series of individual steps in an open and acellular environment using pre-treated plastics together with appropriate combinations of different optimized enzymes, where both desirable degradation products and toxic side-streams can be removed in a continuous fashion (for example, by ultrafiltration).
Group II plastics contain chemical links found in biological molecules, and therefore they are in principle susceptible to natural degradation by enzymes such as esterases and amidases. The greatest progress in biodegradation has been made with PET. One of the first PETases was discovered in the bacterium Ideonella sakaiensis, isolated from a Japanese PET recycling station, which turned out to be a modified cutinase (an enzyme which degrades the waxy substance called cutin covering most plant surfaces)47. It is not particularly thermostable, though, and this is a problem. PET degradation occurs more readily above the glass temperature (between 60 and 80 oC) where the amorphous region of PET becomes more liquid-like and thus more accessible (the crystalline phase remains unaffected as PET melts at 260–280 °C, that is, much higher temperatures). However, various protein engineering approaches have yielded more thermostable enzyme variants. A relatively thermostable PETase (also a cutinase), which has a half-life of 40 minutes at 70 oC, has been isolated from leaf compost48 This enzyme is now being optimized further by multiple research groups around the world in a healthy race to develop the most effective and stable PETase. The record is currently held by a variant developed by the University of Toulouse and the company Carbios, which can degrade PET material to >90% within around 10 hours and with a cost price that is ca. 4% of that of virgin PET49. Encouragingly, the material from this degradation was used to make new PET bottles of the same quality as the originals49. It will be exciting to see if this approach can outcompete current chemical hydrolysis strategies which are highly efficient but require higher temperatures (7 minutes at 250 oC)38-40. Protein engineers have other tricks up their sleeves to improve PETase performance further, for example, by attaching “homing devices” in the form of binding domains that improve the ability of the enzymes to bind to their plastic substrates50. Finally, researchers have managed to engineer the photoautotrophic diatom C. tricornutum to overexpress and secrete bacterial PETase in seawater, which opens up possibilities for large-scale bioremediation efforts51 powered by sunlight.
The enzymatic degradation of PUR is not quite as far in the development, reflecting the polymer’s more complex chemical structure. It contains ester bonds and amide (urethane) bonds, and both must be cleaved for efficient recycling. Enzymes found to degrade PU largely target the ester bonds52. However, there are intense efforts underway based on high-throughput screening from a diversity of genetic sources, and promising urethanases have very recently been identified53. This work is also encouraged by the many high-value products that can be obtained from PU, including alcohols, acids, and aromatic precursors for the chemical industry52.
Prospects for enzymatic recycling of plastics: In summary, with the exception of PET, for which scalable production facilities are currently under development, we still lack well-defined and well-characterized enzymes to attack plastics. We need to develop novel screening methods to identify new plastic degrading enzymes as efficiently as possible and to understand the molecular mechanisms by which these high molecular weight petropolymers are broken down. While such systems may, over the next decade, assume a significant role in biochemically recycling our plastic waste, they will not magically transform our current wasteful plastic consumption, nor will they address the enormous amounts of micro- and nano-plastics which accumulate both on land and in the sea. Moreover, to be able to recycle plastics, we need to first become much better at efficiently collecting our plastic waste on a global scale. The next section will consider the challenges posed by how this is currently done.
The Global Waste Management Context
Around two billion people worldwide lack access to municipal solid waste collection services. Collection coverage ranges vary globally and regionally: North America, 100%; Europe, 80–100%; Latin America and the Caribbean, 80–100%; Asia, 50–90%; and Africa, 25–70%54. Rural areas tend to have less coverage than urban areas, including a complete lack of coverage in some cases55. When there is coverage, it can be infrequent—with long wait times between collection—or inconvenient—with collection occurring at locations far away from households or small 56. Amid such patchy collection, concerns about ritual purity, hygiene, or sorcery can lead to the burning or dumping of certain kinds of wastes (for example, clothes, diapers, or sanitary pads)57-59. Moreover, even with waste collection coverage, low-income households (also in the Global North) may choose to burn or dump their wastes to avoid or reduce collection fees60-62.
In areas with waste collection services, the nature of those services can vary widely, from coverage through the public sector, the private sector, a mixture of both, or through the informal sector, such as micro- or small-enterprises, community-based organizations, or NGOs54. Friction and a lack of coordination between various arms of waste collection services are common, especially in the Global South, and can result in waste leaks or open burning to reduce trash volumes or make to make wastes “go away”63. Complex governance regimes, resource-poor settings, and realities of corruption also mean that waste management officials across most of the globe must navigate diverse and often contradictory funding and policy directives64,65.
An informal waste economy plays an important role in plugging the waste collection gaps left by local authorities in much of the Global South. The informal waste economy is informal in the sense that the services provided by this economy are not paid for by the state. Informal recycling economies typically comprise waste pickers, itinerant buyers, scrap dealers, and other scrap materials traders, and such an economy recovers large volumes of waste material for recycling, reducing the burden on dumping grounds and of uncollected wastes66-69. However, when it comes to plastics, such recovery focuses on high-value wastes, such as PET bottles, that are relatively easier to collect. Thus, smaller pieces of plastic waste, such as sachets or torn pieces of packaging, that require more labour-intensive effort to collect, wastes deposited in difficult to access areas, and plastics with lower scrap value are typically ignored.
In the Global South, the segregation of wastes for recycling usually occurs through the efforts of waste pickers, often at dumping ground sites, rather than at source. In some places, there is even active resistance to segregation-at-source as it requires thought, effort, and space from end users and households70,71. In the Global North, where segregation-at-source is increasingly being encouraged as the norm, non-sorting behaviour and misunderstandings regarding what plastics are recyclable, how to separate them, and how to clean them abound, resulting in mixed or unclean wastes72,73. Even when wastes are appropriately segregated, further separation (that is, to separate out different polymers from mixes) is required. Whereas technology exists for sorting at an industrial scale, for example in the case of PET bottles with PE bottle caps, reliance on manual labour is the norm in most of the world. Managing high volumes of non-biodegradable wastes is a challenge even for OECD countries, and wastes are frequently shipped to lower income countries (with lower labour costs) for segregation and purported recycling. China was the favoured destination for such shipping until 2018, when it implemented a ban on low-quality waste imports under its Operation National Sword74. The policy had major consequences for international recycling, as countries in the Global North were faced with growing piles of plastic scrap that they could not process. Trade in recyclable scrap was displaced onto other low-income countries, such as Indonesia, Turkey, and Vietnam. Once shipped to these countries, wastes are segregated and cleaned, and those that cannot be recycled are often dumped or burned in the open75-77. The cleaning also presents problems, as lack of regulations mean that the runoff is often discharged into open sewers and the soil with obvious adverse environmental consequences.
The question of economics and resources is significant. Low- and middle-income countries typically lack adequate waste management resources. Of the total municipal solid waste generated in 2016, 93% in low-income countries and 66% in middle-income countries was deposited in open dump sites rather than in scientifically managed landfills, which control emissions of landfill gases and leachate that otherwise enters the soil and groundwater78. Mixed wastes generate landfill gases, which are not managed at dump sites79, and the decay of biodegradable wastes is an exothermic process, which produces heat. Under those conditions, temperatures at dumping grounds can rise above the auto-ignition temperatures of landfill gases such as methane. Thus, these highly flammable gases can catch fire, leading to dumping ground conflagrations that wastefully feed off—and consume—high calorific-value plastic deposits.
Recovery of wastes from dumping grounds is further complicated by the fact that organized criminal gangs often wield control over these grounds and the materials there80-82. Criminal involvement in waste management is not limited to control over dumping grounds in the Global South. It also negatively affects waste flows, landfill locations, and landfilling volumes in countries in the Global North83.
The Need for Transdisciplinary Approaches Across the Plastic Life Cycle
Given all these challenges, the effective implementation of sustainable technologies for plastic control will require the development and implementation of solutions that are integrated into their real-world contexts. Plastic waste collection, segregation, and storage systems, as well as laws and policies for their appropriate regulation, will need to be developed while bearing in mind local capacities—including, for example, waste pickers and the informal economy, constraints, and sociocultural contexts. Not just systems but also technologies will have to adapted; to be cost-effective and feasible, for example, bioreactors and technologies cannot merely be scaled up but will also require localization to regional variations in feedstock, temperature, humidity, and sun exposure, among other factors. Such alignment can only be achieved by integrating substantive transdisciplinary collaboration and exchange right from the development stage.
Collaboration will also be required in overcoming roadblocks to change. The primary hindrance is one of economics: how will the costs of implementing new waste and recycling systems be distributed? Are these costs to be borne by taxpayers and the state, plastic industry players, consumer goods’ companies, retailers, consumers, or recyclers themselves? This is a question that already plagues plastic control policies84. Although more salient in low- and middle-income settings, it also presents a challenge for high-income countries. At its core, this question is about which stakeholders are to be held accountable—and to what degree—for plastic wastes. Furthermore, entrenched systems of plastic production, materials recovery, recycling, and disposal, whether formal or informal, bring with them stakeholders invested in the continuation of these systems85. Without buy-in from a significant proportion of stakeholders, implementation will fail. Here, the role of social scientists in developing policies that minimize distributional consequences, incentivize uptake, and promote social justice seems obvious. Yet the natural and technical sciences are essential to fine-tuning technologies and solutions such that they leverage existing infrastructures. Transdisciplinary exchanges will also be crucial to behavioural interventions and eco-literacy campaigns that draw from public understanding of science to build awareness and change social norms towards practices of plastic disposal suited to the new technologies and systems. Such campaigns will have to account for constraints faced by individuals, households, and communities, taking care not to reduce non-compliance to an issue of behaviour or choice alone86. Moreover, such campaigns will be needed to overcome public resistance and misinformation. Finally, technological innovations can have unintended real-world consequences or can raise unforeseen concerns (such as when energy efficiency leads to increased consumption), and collaborative assessment efforts will be needed to monitor such effects and tackle them.
Even when effectively harnessed, scaled up, and translated to divergent real-world contexts, innovations in recycling technologies will address only the end stage of the plastic life cycle, revolving around plastic waste and disposal. Unless such degradation is combined with a reduction in production of virgin polymers, it cannot address issues of a continued dependence upon a carbon economy. Moreover, irrespective of the efficiency of plastic recycling, these processes cannot tackle other aspects of plastic-related pollution and contamination that proceed apace, such as the release of toxicants during plastic manufacturing87,88, the discharge of microplastics and nano-plastics during use, and the leaching of endocrine disrupting chemicals used as polymer additives into the soil, water, and food chain89,90. Tackling the harms of these other stages of the plastic life cycle too will require multi-scalar transdisciplinary interventions that centre issues not just of environmental but also social justice. This is summarized in Fig. 3.
Figure 3. A transdisciplinary approach for interventions across the plastic life-cycle. The red arrow highlights major challenges in the sorting, collection and management of plastic waste
Perspective: A Call for Pragmatic Melioration
Plastics have far too many crucial utilities and are too enmeshed with our lives for us to get rid of them. What, then, is to be done? Environmental crises at the scale of the plastic problem can lead to either a sense of helplessness and cynical resignation or a desperate faith in salvation through human ingenuity and techno-fixes. We make the call for a different stance, one of a transdisciplinary and pragmatic approach revolving around harm reduction. Drawing from the work of the moral philosophers John Dewey and William James, we call this stance pragmatic melioration91. This envisions a middle path between an optimism that sees the world as automatically headed towards progress and a pessimism that views it as irrevocably doomed: it expresses a belief that the world can be improved and made more inclusive through human action92. Through this stance, we advocate a focus on plastic stewardship and continually reducing plastics’ most pernicious harms. This will require foundational studies to identify local and global sources of harm, not just in terms of environmental justice but also in terms of social justice. Emergent technical innovations for plastic recycling will require time to be rolled out. That time can be used to set up such a base of foundational studies and to begin optimizing policies for plastic waste management and recycling that are best suited to their local contexts.
The Pareto principle states that 80% of outcomes can be attributed to 20% of sources. As a heuristic, it speaks to how a relative minority of inputs can affect a majority of outputs and suggests action targeted towards that critical minority. Prioritizing action in accordance with this insight, transdisciplinary teams can work to design localized interventions and policies that target the types of plastics and the plastic life cycle that are linked to maximal harm, especially for the most vulnerable and marginalized. For example, styrofoam, which often escapes waste collection efforts as a result of its light weight and breakability, produces hazardous and combustible styrene gas when openly burned, and is currently not recycled, or small sachets, which are not recycled and often end up as litter or openly burned. Periodic reassessments can then aid the continual targeting and shrinking of harms. Pragmatic melioration, we believe, can be leveraged as a way out of not just our plastic predicament, but it can also provide a model for tackling other environmental challenges and developing socially and ecologically sustainable policies.
D.E.O.’s research on enzymatic plastic degradation is supported by the Novo Nordisk Foundation (grant no. NNF22OC0072891) and the Independent Danish Research Foundation | Green Initiative (grant no. 0217-00125B). G.S.P.’s work on anthropological examinations of plastic use and disposal is supported by the Carlsberg Young Researcher Fellowship (CF-20-0151). We are grateful to Andreas Møllebjerg for constructive comments to the manuscript.
All authors discussed the topics addressed in this Perspective, contributed equally to the writing, commented on the manuscript at all stages, and agreed on the final text. Fig. 1 was produced by D.E.O. and Fig. 3 was produced by G.S.P. and D.E.O. Fig. 2 is reproduced from16 with permission under the terms of the Creative Commons Attribution 4.0 International license.
Declaration of interests
The authors declare no competing financial or personal interests.
CRediT author statement
D.E.O., M.H. and G.S.P. all contributed to conceptualization, writing – original draft and writing – review & editing. No funding acquisition, project administration or supervision was involved in this work.
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