Making Microplastics Matter: Classification,Politics and the Lives of Microplastics as Environmental Objects

Object-centered Classifications: The Making of Epistemic Objects

In laboratories, in workshops and conferences, or in conversations with researchers working on microplastics, the object under discussion is anything but self-evident. One of the first questions after a conference presentation is often deceptively simple: What exactly did you count? Was it everything below 5 mm? Only particles above 10 µm? Were fibers included? What polymers? Using what analytical instrument with which detection limit? Such exchanges are not marginal technicalities. They reveal that microplastics persist as a scientific object only through continuous classificatory work. The object exists because it is repeatedly defined, specified, refined, and contested.

Long before microplastics became a widely recognized public object of environmental concern, plastic fragments were described as present in marine environments (Ryan, 2015). In the early 1970s, oceanographers reported what they called ‘small plastic particles’ encountered during studies of algae and plankton (Carpenter & Smith, 1972)—a key moment frequently recounted in retrospective narratives of the field. What was visible at that time was inseparable from the instrumentation deployed. Early marine studies typically relied on neuston nets with mesh sizes around 333 µm, which effectively set the lower detection threshold for plastic particles (Carpenter & Smith, 1972; Hidalgo-Ruz et al., 2012). What passed through the sieve remained uncounted and, in practical terms, analytically non-existent. Ontological boundaries were thus inseparable from technological limits—a dynamic well documented in laboratory studies (Latour & Woolgar, 1979; Rheinberger, 1997) and still palpable in contemporary debates about detection limits for microplastics.

At that stage, however, these observations did not cohere into a distinct scientific object. Particles were described pragmatically as fragments, pellets, or fibers. They varied in size, color, density, polymer type, and degree of weathering. What existed were scattered descriptions of plastic debris, but no unified object called ‘microplastics’. There was no shared vocabulary, no standardized classificatory scheme, and no stable ontological coherence.

Three decades later, this would start to change when Thompson et al. (2004), in their widely cited article ‘Lost at Sea: Where is all the Plastic?’, introduced the term ‘microplastics’ as a shorthand for ‘microscopic plastic fragments and fibres’. Often narrated as a foundational moment—and celebrated as such within the community, for instance during the 20th anniversary commemorations at MICRO24—this consolidated dispersed observations under a shared label. The paper classified microplastics as a distinct pollution category and emphasized their extent and accumulation. The introduction of the label rendered previously scattered particles communicable and observable across disciplinary boundaries, gradually catalyzing further scientific, public, and policy attention. Labeling, understood here as an initial move in object-centered classification, proved highly productive. Naming the phenomenon enabled aggregation, comparison, and communication. The label did not merely reflect an existing reality but helped organize it. As Daston (2000, p. 13) notes, scientific objects ‘grow more richly real as they become entangled in webs of cultural significance, material practice, and theoretical derivations’. In this sense, the term ‘microplastics’ functioned as a coordinating device: it held together heterogeneous particles without eliminating their internal diversity.

Over time, classificatory practices began to consolidate. Size emerged as particularly consequential—and persistently negotiated—classificatory dimension. Already embedded in the prefix ‘micro’, size determines inclusion and exclusion. It specifically shapes reported quantities: the smaller the detection limit, the higher the particle counts. Size classification thus performs scaling work. It amplifies or attenuates the perceived magnitude of contamination and thus also impacts how the epistemic object is perceived in the public and policy arena.

A key moment occurred during the 2009 workshop of the US National Oceanic and Atmospheric Administration (NOAA), which proposed defining microplastics as ‘plastic particles smaller than 5 mm’ (Courtney et al., 2009). For the first time, a shared upper threshold created a reference point across studies. This marked a moment of provisional stabilization. Conferences and workshops were—and remain—particularly revealing sites for observing fractures and frictions around how to draw boundaries around microplastics—within and beyond NOAA’s initial classificatory move. As Mody (2012) notes for emerging scientific fields, conferences are powerful mechanisms for creating connections among participants and aligning them toward a shared identity or project, especially in areas not yet stabilized through journals or professional societies. In the case of microplastics the 5 mm boundary enabled aggregation. It allowed researchers to speak a shared language, to compare datasets, to count and map occurrences. Yet this stabilization did not eliminate heterogeneity; it organized it. The category ‘below 5 mm’ encompassed millimeter-sized fragments visible to the naked eye alongside microscopic particles with entirely different environmental behaviors. As SAPEA (2019, p. 17), part of the European Commission’s Scientific Advice Mechanism, made explicit, the cut-off at 5 mm is ‘to some extent arbitrary’. The threshold made comparability possible while simultaneously masking internal variation. In conference exchanges and interviews, researchers frequently emphasized this point, questioning how different approaches to studying heterogeneous forms of microplastics could meaningfully speak to one another. The diversity of particles—across size, morphology, polymer type, and degradation state—renders generalization difficult. As Rochman et al. (2019, p. 703) caution, ‘studying the fate and effects of one plastic type with a specific shape and size does not tell us the fate and effects of microplastics in general’.

Unsatisfied with the NOAA’s broad definition (Chae et al., 2023), efforts to refine size categories proliferated. Researchers distinguished between ‘large’ (1–5 mm) and ‘small’ (<1 mm) microplastics (Van Cauwenberghe et al., 2015). Broader frameworks spanning nano-, micro-, meso-, macro-, and mega-ranges were proposed (GESAMP, 2015). Bermúdez and Swarzenski (2021) suggested aligning particle classes with plankton size ranges to ground classification in ecological realities. Increasing attention to nanoplastics—particles below 1 µm—introduced further complexity. Nano-sized particles were argued to possess properties fundamentally distinct from larger particles (Gigault et al., 2018; Koelmans et al., 2015). Rather than closing debate, these refinements multiplied epistemic objects and the reasons to study them also proliferated. Such proposals illustrate that classification is a conceptual struggle over how to render heterogeneity analytically tractable—and how this allows insights to matter in real-world contexts beyond the lab.

These often-theoretical conversations sometimes clashed with practical efforts of sampling and measuring particles (Koelmans et al., 2019). For instance, while some definitions of microplastics in principle include nanoplastics, these remain immensely difficult to study in practice. In the end, detection thresholds—often still around 10 µm in practice—define what becomes visible and measurable. In field settings, this was clearly palpable to us: the object shifted, often depending on methodological choices. During conference Q&A sessions, discussions similarly frequently revolved around measurement instruments and detection limits. Detection ultimately defines what becomes visible and what remains beyond measurement. Classification thus remains inseparable from instrumentation and analytical feasibility.

Through these debates runs a tension between standardization and openness. Thompson (2015, p. 191) contrasts the needs of ‘monitoring science’, which requires defined parameters, with ‘curiosity-driven’ science, for which ‘it might be unwise to set a formal limit to lower size boundary … until there is better understanding about which types/size of microplastics are of concern’. As Poirier (2019) notes, formalizing meaning into infrastructures always entails pragmatic trade-offs: enabling coordination while necessarily restricting complexity. Overly rigid definitions, coupled with persistent uncertainties and limitations in measurement instruments, risk constraining inquiry, epistemic diversity, and openness to future insights (Hartmann et al., 2019; Thompson, 2015). At the same time, monitoring infrastructures—NOAA’s database (Nyadjro et al., 2023), Japan’s Atlas of Ocean Microplastics (Michida et al., 2019), and European monitoring under the Marine Strategy Framework Directive (MSFD Technical Group on Marine Litter, 2023)—require stable parameters to ensure comparability across time and space. Without agreed definitions, aggregation becomes impossible. Similarly, political interventions require stable and actionable regulatory categories; classifications’ feasibility for policy action often became points of reference to judge their usefulness. As Hartmann et al. (2019, p. 1041) note, ‘a globally accepted definition [of microplastics] is an essential prerequisite to tackle the issue, especially from a regulatory perspective’.

Tensions between classifications became increasingly apparent as scientific interest grew and research expanded beyond marine systems into freshwater, soils, the atmosphere, food, and eventually human bodies. With this expansion, classificatory pressures intensified (i.e. Chae et al., 2023; Helm, 2017; Kadac-Czapska et al., 2023; Liu et al., 2019). New disciplines, such as freshwater ecology, soil science, atmospheric science, analytical chemistry, ecotoxicology, materials science, exposure science, biomedical research, entered the field, each bringing distinct epistemic commitments and methodological traditions. With them came new questions, increasingly shaped by public concerns and regulatory desire for action: How do particles move through air? How do they interact with soil matrices? Can they enter the food chain through crops? How do particles enter and interact with human bodies? Can they cross cellular membranes? What constitutes a relevant exposure dose? What are the sources and pathways of microplastics? These shifting problem framings reconfigured classificatory priorities. In toxicology and biomedical research, size became central because of its relevance for biological uptake (Nardi et al., 2024). Smaller particles, especially those in the nanometer range, may cross cellular barriers, intensifying concerns about potential human health effects (WHO, 2022), which is clearly reflected in a fast-growing number of publications in health research over the past decade. In atmospheric science, particle size and form distribution determines transport and deposition (El Hadri et al., 2024). In soil science, polymer composition and density influence interaction with organic matter and uptake in crops (de Souza Machado et al., 2018; Gan et al., 2023). What counts as salient thus depends on the research context.

These tensions surfaced repeatedly in ethnographic encounters. Researchers express frustration about incomparability between studies while defending methodological specificity. One laboratory prioritizes polymer identification; another focuses on particle size; a third emphasizes toxicity assays. Each claims to study ‘microplastics’, yet the underlying objects differ. Classification does not simply transport meaning unchanged but transforms what it describes (Latour, 2005). Classificatory practices structure scientific inquiry under conditions of uncertainty; making particles measurable, comparable, and analyzable—yet without a shared vision of what (and for what reasons) should count as microplastics. Scientific classifications are sites where facts, concerns, and forms of care are continuously recomposed. Classifications are negotiated with empirical measurements (fact making), which are in turn inseparable from varying concerns about marine environments, aquatic ecosystems, food quality, or human health as well as requirements for emerging infrastructures of monitoring and mitigation to care for the particles. Knowledge production, research priorities and financing are, at least implicitly, shaped by anticipated harm, public concerns, regulatory demands, and potential future interventions. These registers do not unfold sequentially; they circulate within scientific debates themselves, sometimes being a justification for doing this kind of research and sometimes as a proof of relevance for their work.

‘Microplastics’ functions as a capacious container, holding together multiple, only partially overlapping epistemic configurations. It enables funding streams, interdisciplinary collaborations, public communication, and regulatory engagements. Growing environmental attention, together with the rapid rise in publications and research projects over the past decade, reflects the productive capacity of a shared label. Yet this coherence remains provisional. Detection limits shift. Nanoplastics are separated out or folded back in. Discrete categories are challenged by continuous distributions. Rather than converging toward a singular, fully stabilized epistemic entity, microplastics persist as a dynamic field of alignment work.

As the label circulates beyond scientific settings, this internal multiplicity does not disappear. Instead, it is reconfigured. The next section examines how object-centered classificatory negotiations within research intersect with broader processes through which microplastics are assembled as an object of public concern.

Labeling and Mediatizing: The Making of a Public Object

For a long time, what we now call microplastics existed without broader public resonance. Small plastic fragments were observed, measured, and occasionally discussed in marine science, but they did not circulate beyond specialized communities. They lacked not only a stable scientific definition, but also the language, imagery, and framing necessary to render them publicly intelligible. To draw on Latour’s (1999, p. 115) formulation, microplastics moved over the past decades from a ‘nonentity’ to what today appears as a ubiquitous environmental threat—an object seemingly present across oceans, soils, air, food, and bodies. This transformation did not follow automatically from the accumulation of scientific findings; it required sustained work to make microplastics visible, nameable, and communicable.

Earlier engagements with plastic pollution focused primarily on marine litter: visible debris, entangled animals, floating garbage patches, beach contamination (Ryan, 2015; Schmid et al., 2021). Plastic pollution was framed as a problem of waste, overconsumption, and individual responsibility (Liboiron, 2012). The ocean was imagined as an ‘ultimate sink’ (Tarr, 1996), and pollution as something accumulating at distant shorelines or ocean gyres (Bergmann, 2019; Phillips, 2017). This framing localized the issue and attached it to specific moral narratives—littering, recycling, clean-up campaigns. It did not foreground microscopic persistence or circulation through air, soil, food, and bodies. Industry efforts to defer responsibility only reinforced the idea of plastics as issue under control (Clapp, 2012; Mah, 2021). As we observed in citizen discussion groups conducted in our project, plastic, as a material, still frequently serves as the primary framing device, with ‘microplastics’ often treated as a secondary or derivative concern. Moreover, for decades, there was little imagination that plastic fragments might persist and accumulate as microscopic particles. Early assumptions that plastics would degrade without residue reinforced their invisibility (Gregory, 1983; Scott, 1972). Without a shared label and without a narrative of persistence, small plastic particles could remain what Zerubavel (2015) calls ‘hidden in plain sight’. They were present but not assembled into a coherent object of concern.

The consolidation of the term ‘microplastics’ marked a decisive shift. As shown in the previous section, labeling functioned as a move within oceanographers’ classificatory practice. Yet its consequences extended beyond epistemic coordination. By naming microplastics as a distinct pollutant, researchers created a communicable object capable of circulating beyond scientific communities and developing a life of its own. The label subsumed diverse phenomena—seabird ingestion of fragments, pellet loss during production, microbeads in cosmetics, particles in remote glaciers, seafood, bottled water, and human tissues—under one encompassing category. It condensed spatially and materially dispersed observations into a recognizable environmental issue, shifting attention from visible litter to diffuse and pervasive contamination.

Drawing on Latour’s (2005) observation on the connection of issues and publics, the emergence of microplastics as a public object can be understood as a process of issue-formation rather than simple diffusion of scientific knowledge. The consolidation of the label did more than stabilize a scientific category; it enabled heterogeneous particles to assemble publics around them. While Latour does not explicitly theorize classification, his account of how objects become matters of concern helps illuminate naming as a political and communicative act: It gathers dispersed material phenomena into a controversy, making them visible as something to be debated, measured, and acted upon.

At the same time, the force of the label did not rest on naming alone. Its stabilizing effect depended on infrastructures of circulation—media routines, NGO campaigns, survey instruments, policy referencing, and institutional relocation into arenas such as food safety governance. Through repeated citation, measurement, and institutional uptake, the category ‘microplastics’ was made salient, and then continually reassembled as an object warranting attention.

This process unfolded gradually rather than instantaneously. For several years, microplastics remained embedded within broader concerns about plastic pollution and marine litter. European media and policy debates initially focused on visible waste rather than microscopic particles. This is reflected, for example, in the 2017 Eurobarometer on environmental attitudes (EC, 2017), where microplastics were not explicitly addressed. Only subsequent surveys expanded the framing of microplastics beyond environmental concerns to include food safety and human exposure, thereby shifting institutional attention toward bodies such as the European Food Safety Authority (EFSA). This reframing altered both perception and governance arenas. In 2019, for example, the EFSA’s survey asked to what extent Europeans were ‘worried about the environmental impact of microplastics,’ with 48% responding that they had heard of microplastics in food and 21% expressing concern—though with considerable variation across countries (European Food Safety Authority [EFSA], 2019). The 2022 and 2025 surveys further documented rising public concern, with microplastics ranking among the highest perceived environmental risks in some countries (EFSA, 2022, 2025). National data illustrate similar trajectories. In Germany, for instance, more than half of respondents in 2015 reported having heard about microplastics in food, even though the issue was not yet institutionalized as a distinct regulatory risk category (BfR, 2015). By 2023, concern had increased significantly, with microplastics ranking among the most salient perceived food-related risks (BfR, 2023). The object had moved from a specialized research topic to a widely recognized public concern.

Media dynamics played a central role in this process. As Schönbauer and Müller (2021) show for Germany, from 2004 to 2018 microplastics gradually shifted from a relatively obscure research topic to a prominent environmental and health issue. Media coverage increasingly framed them as concrete risks, even as peer-reviewed research often emphasized uncertainty, context-dependence, and methodological limitations. Völker et al. (2020) demonstrate similar dynamics for the UK. The epistemic object—characterized by heterogeneity, methodological limitation, and ongoing debate—took on a different configuration in the public arena, where the threshold for what counted as actionable knowledge shifted and potential harm was foregrounded more categorically.

This reconfiguration did not go unnoticed in scientific communities (Koelmans et al., 2017). While appreciating public attention their research received, several interviewees described the public trajectory of microplastics as driven by communicative amplification. As one expert in water quality management noted: ‘I think microplastics are more of a problem of communication. When I see something like that, it is alarming, of course. But that has nothing to do with the issue at hand. And I would say that what the general public is concerned about is not actually what scientists are talking about.’ Another toxicologist emphasized that ‘the mere presence of a substance does not in itself pose a problem’, suggesting that in public discourse presence itself had become sufficient grounds for concern. Ultimately, he suggested that matters of concern had come to outweigh toxicological fact-finding, crystallizing in what he described as the dominant position in the public arena: ‘I don’t care whether it’s toxicologically relevant or not, I just don’t want it. Period.’

Such statements illustrate that the public object ‘microplastics’ does not simply mirror the epistemic one. Rather, it emerges through communicative practices that selectively amplify certain dimensions. This amplification contributed to a reconfiguration of how uncertainty was handled across arenas: while scientific publications continued to emphasize methodological limitations and context-dependence, public discourse increasingly treated ubiquity and potential exposure as sufficient grounds for concern. At the same time, scientific debates increasingly re-entered the public arena. Reviews highlighting the lack of standardized sampling and analysis protocols (Koelmans et al., 2019) and controversies over nanoplastic quantification (Materić, 2024; Monikh et al., 2025) have been reported in media outlets. Widely publicized claims about microplastics in human tissues have been challenged for methodological limitations and contamination risks (Carrington, 2026), generating public ambivalence about what is known and what remains uncertain.

Recent popular science books and documentaries further illustrate the cultural work involved in assembling microplastics as a public object. A popular book (Simon, 2022) is titled ‘A Poison Like no Other’, one documentary calls them a ‘a hidden crisis’ (Addelman & Tong, 2024), and another maintains that they are ‘everywhere, invisible, deadly’ (Harlander, 2024). As narratives translate scientific findings into emotionally resonant stories, the invisibility of microplastics becomes a source of heightened attention—unseen particles that circulate through bodies invite a distinct form of concern.

Importantly, labeling also reconfigured and augmented older environmental debates. Long-standing concerns about marine litter, air pollution, sewage sludge reuse, or particulate matter were reinterpreted through the lens of microplastics. Civil society actors and environmental campaigns adopted and amplified the label. Efforts previously centered on marine litter were reframed through the language of microplastics. The Plastic Soup Foundation’s campaign against microbeads exemplifies this shift: Microbeads became emblematic of the broader microplastics issue. The label provided a focal point for mobilization. In Austria, the public articulation of microplastics contributed to visible policy responses, including revised sludge management regulations. From 2033 onward, sewage sludge from wastewater treatment plants serving more than 20,000 population equivalents must be thermally treated rather than applied to soils—an intervention widely discussed effort in ‘the fight against microplastics’ (Langer, 2024). Similarly, as one interviewee observed, particles previously discussed as ‘fine dust’ were now reframed as ‘microplastics’, acquiring a different affective and moral charge. ‘Today,’ he noted, ‘it’s suddenly this very frightening thing’. The label did not invent particles in the air, but it transformed their significance.

The trajectory of microplastics as a public object illustrates the productive ambiguity of what Bos et al. (2014) call a ‘big word’: a capacious category that enables multiple interpretations and mobilizations. Precisely because they encompass diverse materials, pathways, and effects, ‘microplastics’ functions as a rallying point across activism, journalism, and policy. Its openness facilitates translation between domains with different evidentiary standards and temporalities.

Yet the label alone did not produce public salience. Its force depended on infrastructures of circulation—survey instruments, media routines, institutional relocations into food safety governance, NGO campaigns, and attention in policy—that stabilized concern and rendered it measurable. Through Eurobarometer questions, EFSA surveys, popular science narratives, and regulatory debates, microplastics were repeatedly viewed as warranting attention. The public object emerged through the alignment of communicative, institutional, and affective practices.

In this process, the relation between matters of fact and matters of concern was not one of simple distortion or exaggeration. Rather, the evidentiary thresholds shifted. Within scientific practice, uncertainty and methodological limitation remain central organizing principles. In public arenas, by contrast, ubiquity and potential exposure became sufficient grounds for concern. Presence itself acquired normative weight. What counts as actionable knowledge differs across these arenas.

Importantly, the public object does not replace the epistemic one. Nor does it merely simplify it. Instead, it reconfigures scientific heterogeneity into a communicable and mobilizing form. Scientific debates about detection limits, nanoplastics, or measurement protocols re-enter public discourse, while public concern feeds back into research agendas and funding priorities. The boundary between epistemic and public object is therefore porous and dynamic.

The case of microplastics thus extends STS analyses of classification and public problem formation. It shows how a shared label can coordinate heterogeneous phenomena across arenas without resolving their ontological multiplicity. It also demonstrates how public stabilization operates not through closure, but through repetition, amplification, and institutional embedding. What appears as a singular environmental threat is sustained by ongoing translation work across regimes of fact-making, concern articulation, and emerging forms of care.

Source-centered Classifications: The Making of Regulatory Objects

If the public arena amplifies microplastics as a diffuse and ubiquitous threat, and scientific practice reveals their classificatory instability, the regulatory arena confronts a different challenge: how to render this expansive and heterogeneous object legally actionable. To become governable, microplastics must be translated into categories that are measurable, attributable, enforceable, and compatible with existing legal frameworks. The shift from matter of concern to matter of regulatory care thus requires a further round of classificatory work.

European Union initiatives to regulate microplastics exemplify this process. Under the Action Plan Towards Zero Pollution for Air, Water and Soil (EC, 2021), the EU has set a target to reduce microplastics emissions by 30%. Measures include expanded monitoring across environmental compartments (marine systems, freshwater, wastewater, drinking water, sewage sludge) and, most prominently, the 2023 restriction of ‘intentionally added microplastics’ under REACH (the EU’s Registration, Evaluation, Authorisation and Restriction of Chemicals framework) (EC, 2023).

Regulating microplastics posed a considerable challenge: transforming a scientifically unsettled and publicly amplified phenomenon into an object of possible intervention—without destabilizing complex economic infrastructures. In the process, scientific were translated, narrowed, disaggregated, and selectively reformulated. Epistemic concerns about persistence, measurability, and environmental behavior intersected with regulatory considerations of feasibility, proportionality, enforceability, and market harmonization. Policymakers operated in a space shaped by heightened public attention and incomplete evidence, where precautionary reasoning coexisted with economic constraint.

This regulatory momentum unfolded alongside increasing expressions of scientific and institutional caution. Some experts warned that regulatory action might ‘lose sight of science’ (Burton, 2015, 2017) and that microplastics risk becoming a ‘convenient but distracting truth’ (Backhaus & Wagner, 2018; Stafford & Jones, 2019). Policy-informing documents likewise foregrounded the absence of conclusive evidence linking microplastics to specific health outcomes (Vercauteren et al., 2023). Regulation thus emerged from a political and institutional context in which precaution, public pressure, and epistemic uncertainty coexisted.

The European regulation of microplastics can be understood as a form of anticipatory governance. As one European Commission expert explained: ‘at a certain moment, on microplastics we felt we need to do something because the pressure is too high from everyone [the public]’. Established regulatory tools, particularly risk assessment grounded in dose–response thresholds, proved difficult to apply to a phenomenon characterized by persistence, accumulation, material heterogeneity, and diffuse pathways. Policymakers faced divergent temporalities: the slow pace of scientific consensus-building and the political imperative to demonstrate responsiveness and care for environmental concerns. As one interviewee described:

We could spend another 20 years discussing and eventually reach a compromise on a definition, a method, a monitoring and perhaps a limit value … But we would simply be wasting a huge amount of time and, in the meantime, more and more polymers and plastic products would end up in the environment. We wouldn’t be solving the problem. … This debate is always very scientific.

This temporal friction is central. Whereas scientific classification aims at refinement and consensus, regulatory classification must produce decisions under conditions of incomplete stabilization.

Kramm’s (2023) analysis of the REACH restriction shows that this required the European Chemicals Agency (ECHA) to move beyond conventional chemical risk paradigms. Rather than regulating microplastics through toxicological thresholds, ECHA justified restriction on the basis of persistence and environmental accumulation. Microplastics, Kramm argues, ‘cannot be treated like a classical chemical’ that becomes problematic only beyond a defined limit; they are instead governed as material pollutants whose presence itself is problematic (p. 12). The regulatory object thus departs from toxicology-centered classification and aligns more closely with waste governance logics.

To operationalize intervention, regulators developed what Laurent (2022) calls ‘regulatory categories’—administratively tailored classifications designed to distribute responsibility and enable targeted measures. In the case of microplastics, this took the form of what we term source-centered classifications. Unlike object-centered scientific classifications, source-centered categories organize microplastics according to their pathways into the environment.

The European Commission currently distinguishes four such categories (EC, 2018; Hann et al., 2018; Scudo et al., 2017): (1) microplastics intentionally added to products (e.g., cosmetics, detergents, paints, fertilizers, artificial turf), (2) microplastics released during the production, transport, and use of plastic pellets, (3) microplastics generated through wear and tear of products such as tires, paints, and synthetic textiles, and (4) microplastics resulting from the fragmentation of larger plastic waste. These categories draw loosely on scientific distinctions between ‘primary’ and ‘secondary’ microplastics—the former describing manufactured microplastics and the latter particles coming from degradation of larger plastics (Andrady, 2011; Cole et al., 2011)—but reconfigure them around regulatory steerability. Their purpose is to identify intervention points. The EC’s categories are explicitly created to facilitate regulatory steering, allowing authorities to identify controllable origins, set intervention priorities, and assign responsibilities. They thereby translate scientific descriptors into entities legible to governance, in ways that necessarily incorporate economic, industrial, and market considerations alongside environmental concerns.

Only the ‘intentionally added’ category has been subject to outright restriction under REACH (EC, 2023). Its framing as deliberate addition renders it relatively straightforward to regulate. By contrast, wear-and-tear emissions—although quantitatively more significant—are deeply embedded in mobility systems, consumer practices, and industrial infrastructures. Here, regulatory efforts focus on mitigation measures such as product redesign, labeling, and technological capture. Fragmentation from plastic waste remains largely addressed through circular economy and waste policies. The regulatory landscape thus multiplies categories according to jurisdictional competence and political feasibility rather than environmental magnitude.

The evolution of the category of ‘intentionally added microplastics,’ which ultimately provided the basis for the European Commission’s 2023 REACH restriction (EC, 2023), further illustrates how facts, concerns, and visions of care become intertwined in the making of regulatory objects. The European ban built on earlier environmentalist mobilizations and national restrictions targeting microbeads—small plastic particles intentionally added to cosmetics for exfoliation, visual appeal, or texture. Nongovernmental actors such as the US-based 5 Gyres Institute and the Dutch Plastic Soup Foundation’s ‘Beat the Microbead’ campaign began raising public awareness already in the early 2010s (Dauvergne, 2018). Their framing of microbeads as emblematic of unnecessary and preventable pollution translated diffuse scientific observations into a concrete and morally charged regulatory target. Several countries, including Ireland, France, and Sweden, subsequently adopted national restrictions.

When the European Commission moved toward Union-wide regulation, harmonization of the internal market became a central justification. As the Commission (EC, 2023, p. 2) explicitly stated:

Several Member States have adopted or proposed dedicated measures. However, a patchwork of national restrictions potentially hampers the functioning of the internal market and therefore requires harmonization at Union level.

Environmental concern and market integration thus advanced together. The regulatory object of ‘intentionally added microplastics’ was shaped as much by the need to safeguard economic coordination as by the desire to reduce pollution.

The initial articulation of this category appeared in a 2017 expert report commissioned by the Commission (Scudo et al., 2017). In its broadest formulation, it encompassed ‘microplastics that are intentionally added to products, such as personal care products, detergents, paints, abrasives, agriculture, and others’ (p. 6). Regulators quickly judged this definition ‘too broad to be workable’ (p. 41), because it risked sweeping in extensive industrial sectors. The category was therefore disaggregated into product-specific sub-classifications, with definitions crafted to meet regulatory criteria of feasibility and proportionality. Strikingly, the report acknowledged that ‘the more detailed the definition, the lower the economic effects are expected to be’ (p. 104). Here, granularity functions as a calibration technique: Tightening the definition reduces industrial disruption while maintaining regulatory appearance. Economic considerations were not external constraints imposed after the fact; they entered into the very delineation of what counted as microplastics for regulatory purposes.

The cosmetics sector exemplifies this dynamic particularly clearly. A broad definition of microplastics as ‘synthetic polymers smaller than 5 mm’ would have ‘the most severe impact on virtually all classes of cosmetic products’, rendering numerous formulations unviable and requiring alternative technologies ‘not available and [that] would take years/decades to develop (if at all possible)’ (Scudo et al., 2017, p. 218). A narrower definition—restricting ‘any intentionally added, ⩽5 mm, water-insoluble, solid plastic particle used to exfoliate or cleanse in rinse-off personal care products’—would instead target only those particles ‘capable to contribute to marine litter’ (p. 219), substantially reducing economic impact while preserving environmental intent.

The lower size limit became a central site of contestation because it determined inclusion and exclusion. Industry representatives such as Christian Block from Plastics Europe advocated for a 1 µm cut-off, warning that broader definitions would encompass ‘widely-used opacifiers, film-formers and bulking agents’ and thereby destabilize soap and detergent formulations (Wray, 2018). NGOs, by contrast, argued for no lower limit, warning that narrow definitions would create ‘unjustifiable loopholes’ and might incentivize the use of smaller particles, which were often suspected to be more toxic (Prabhakar, 2019). The European Commission ultimately settled on a 100 nm lower limit, citing ‘significant practical concerns, including regarding enforcement’ (EC, 2023, p. 3)—notably the lack of measurement capacity in the nano range.

This decision reveals how enforcement capacity, measurement technology, economic proportionality, and environmental ambition intersect in the regulatory stabilization of microplastics. What counts as microplastics under REACH is the outcome of, on the one hand, scientific characterizations, and, on the other, institutional negotiation over what can be detected, controlled, and harmonized within the single market. The evolution of ‘intentionally added microplastics’ thus demonstrates that regulatory classification is a site of co-production. As definitions become more granular, microplastics acquire regulatory properties shaped by industrial infrastructures, measurement technologies, and market logics alongside environmental science. The object shifts from a heterogeneous environmental contaminant to a legally circumscribed category whose boundaries are calibrated through feasibility, enforceability, and proportionality.

In this sense, the regulatory object is neither a direct translation of the epistemic object nor a mere response to public concern. It is a reconfiguration that selectively brackets scientific multiplicity and public amplification in order to stabilize intervention. Source-centered classifications do not aim to resolve ontological uncertainty; they partition it into administratively manageable domains. Persistence replaces toxicity as organizing principle; controllability replaces comprehensive characterization.

The making of regulatory categories for microplastics shows how environmental governance proceeds without epistemic closure. Rather than waiting for definitive toxicological thresholds, regulation advances through source-based classifications that redistribute responsibility and align environmental care with market compatibility. What microplastics are, in regulatory terms, becomes inseparable from what can be feasibly governed. Classification here operates as a descriptive and communicative practice while simultaneously functioning as an instrument of anticipatory care under constraint.