Introduction
Emerging from early nanoscale research in the 1990s [
1], carbon nanotubes (CNTs) have earned a reputation for being the paradigmatic example of nanotechnology [
2]. CNTs are carbon nanofibers with high aspect ratios, i.e., with much longer lengths than diameter [
3,
4]. Both single-wall and multi-wall CNTs share useful properties, such as high strength, conductivity, and corrosion resistance [
3], and may serve as a substitute for rare metals [
3]. Since the 2000s, CNT applications have proliferated and the material is now used across various fields, from material coatings, composites, microelectronics, and batteries [
5,
6], to water purification and drug delivery [
7]. In a recent review, Temizel‑Sekeryan et al. [
5] find production estimates between a few thousand to 20,000 metric tons in the first half of the 2020s.
This commercial success story has also been marked by scientific and regulatory disputes about the classification, standardization, and ultimate implementation of CNTs in society, which parallel longstanding discussions on the potential environmental implications of nanotechnologies [
8]. These issues remain contentious and unresolved [
7,
9], as is common for nanomaterials in general [
10‐
12]. In November 2019, this contentiousness was made more acute by the publication of a
Nature Nanotechnology article, in which the Swedish NGO ChemSec pointed to the potential hazards of CNTs [
13]. ChemSec, or the International Chemical Secretariat, “[…] is an independent non-profit organization that advocates for substitution of toxic chemicals to safer alternatives”, through “[…] independent research, cross-border collaboration and practical tools” [
14]. These substitution efforts are targeted at corporations, with various online tools to help evaluate products that might contain hazardous chemicals.
With CNTs, a nanomaterial was added to the organization’s SIN (short for Substitute-It-Now) list of hazardous chemicals for the first time [
15]. This was remarkable, as the SIN list evaluates materials on the basis of the very same criteria as the European Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulation [
13], suggesting that CNTs should become subject to future EU regulation. ChemSec implicitly supports this claim by stating that “out of all the substances that are officially regulated under REACH today, ChemSec named over 94% of them well ahead of the authorities,” on their website [
16]. However, the SIN list has no direct legal implication and avoiding SIN entries in products is voluntary. Still, Hansen and Lennquist [
13] assert that many companies (e.g., H&M, AkzoNobel, and Scandic) are aware of and make decisions about their chemical use in consultation with SIN to highlight its industry relevance. The implications of this development might thus be significant for the CNT industry.
Following ChemSec’s decision, a debate ensued in the journal
Nature Nanotechnology: should CNTs be substituted or not? [
7,
9,
13,
17,
18].
Nature Nanotechnology “aims to be the voice of the worldwide nanoscience and nanotechnology community” [
19]. This community extends from the natural sciences to the “broader nanotechnology picture,” including “funding, commercialization, ethical, and social issues” [
19]. The journal promises “independence from academic societies and other vested interests,” high-quality science, and lists social diversity as well as science for “positive change” as guiding editorial values [
20].
The aim of this paper is first to analyze the main theses and arguments of the debate about CNT substitution. Second, this leads to an exploration of the implicit values that underpin the arguments for and against CNT substitution. This demonstrates that the debate—which is presented by protagonists and antagonists as a technocratic conflict about facts—is equally about value-laden preferences in the management of technology (cf. [
21]). Swierstra and Rip [
22] introduced this journal,
NanoEthics, by presenting two models for ethical discussion about nanotechnology: the Athenian
agora and the Machiavellian
arena. In an agora, the forum is deliberative, and issues are resolved by reaching consensus. The arena is instead seen explicitly as a space of competing interests, “where some win and others lose.” Here, the consensus is illusory, and compromise is the goal. The present work attests to the debate about CNTs as a combined agora-as-arena in the sense that the arena masquerades itself as an agora.
The focus on CNTs addresses a gap in the literature on the above social and ethical issues [
21,
23] in the “broader nanotechnology picture.” With various social science [
24‐
26] and applied ethics [
22] approaches investigating the nexus of nanoscience, nanotechnology, and society, there is a lack of research at the level of specific materials, products, and technologies, especially as nanotechnologies begin to mature [
27].
1 Previous research has produced generalist accounts of nanoscale-to-society relations, notably building upon two principal research perspectives. One is the public and expert perception [
34,
35] and engagement with nanotechnology in a broad sense [
36‐
39]. The other is oriented towards policy-making practices for science, technology, and innovation (STI) [
40,
41], often explicitly to strengthen trust and legitimacy [
42]. This includes aligning research and innovation with societal values, as typified in Europe with Responsible Research and Innovation (RRI) [
43], after rising lay “backlash” [
44] to emerging technologies like GMOs that preceded nanotechnology in the 1980s and 1990s [
45]. In contrast, this article seeks to understand the regulatory and ethical discussion about the specific nanomaterial CNT.
The article is structured as follows: after a brief methodological description (Sect.
2), the subsequent section contains a mapping of the arguments of the opposing camps in the above-mentioned debate (Sect.
3). The next section analyzes the implicit values that help explain the latent fissures of the debate (Sect.
4). The article is concluded by a restatement of the thesis and a call for further studies of the implicit institutionalization of values and ethics for CNTs and other nanomaterials.
Discussion
As shown above, the two camps provide various arguments for and against the substitution of CNTs as implicated by the SIN listing. Some of these arguments to a large extent regard matters of fact, such as whether CNTs—all or some—are carcinogens. However, some of the arguments posed by the camps are not only about such technical matters of fact. The use of technologies in society—here with CNTs—is never value-free [
23]. This debate thus oscillates between an explicit technical and implicit ethical dimension, as proposed by Swierstra and Rip:
“The focus on technical questions is only
possible when some closure of the open-ended ethical (or normative, or
political, or foundational) debate has occurred, and further discussion can be
delegated to technical–analytical work. Conversely, the technical discussion can
be opened up again to ethical discussion when the assumptions protecting the
technical approach are questioned” [
22].
This section will unravel how these assumptions are contested by the mobilization of values, both by the pro- and contra-substitution camps. Three intrinsic values, or final values, emerge from the arguments (as illustrated by Fig.
1): (i) environmental protection and human safety, (ii) good science, and (iii) technological progress. The pro-substitution camp largely invokes environmental protection and human safety, whereas the contra-substitution camp also relies upon the values of good science and technological progress—all three values. These intrinsic values are not made explicit, with the exception of the progress argument used by the contra-substitution camp but can be inductively derived from the arguments. Nevertheless, the debate revolves around the two camps not agreeing on the best means to safeguard such values, as developed below.
Environmental Protection and Human Safety
The pro-substitution camp sees unharmed environments (including non-human organisms) and human safety as the main value to be safeguarded, as foregrounded in the hazard and asbestos arguments. This is also clear from the emphasis on effectively functioning safety regulation, as emphasized in the regulatory feasibility argument. Regulatory feasibility is a norm to be defended even when in conflict with, for example, the scientific norms of precision (the case-by-case argument) or standardization (the lack of standardization argument). Scientific experimentation on CNTs produces the empirical evidence to inform regulatory action, but regulatory and scientific reasoning should not be conflated. Science is the means of regulatory ends to safety.
The pro-substitution camp’s review of available evidence concludes that CNTs are hazardous in the regulatory sense (i.e., the hazard argument). However, the contra-substitution camp argues against a conclusion on the higher CNT level because of either (i) inconclusive or non-standardized, unreliable research (in the lack of standardization argument) or (ii) outcomes varying across CNT morphology (in the case-by-case argument). This opposing viewpoint by the contra-substitution camp uses available experimental data to tell a different story: CNTs do not merit group-level categorization and regardless, they are not demonstrably hazardous.
As both camps refer to empirical work through nanotoxicology studies, the key contention is not the availability of testing, but how to interpret results and thereafter shape regulation—a point detailed by Philbrick’s paper [
49] for the asbestos argument. One way to deal with this uncertainty, or “ignorance” in Swierstra and Rip’s lexicon [
22], is by directly taking action—developing regulation from assumed ignorance, instead of delaying under the promise of stable knowledge in the future. This rationale is akin to the precautionary principle, which encourages action to prevent or avoid potential risks in the absence of scientific certainty and the capacity to undertake comprehensive risk assessment [
54]. There is a clear appeal to the precautionary principle as a way to proactively regulate under uncertainty [
55‐
57].
However, the contra-substitution camp both (i) claims that the precautionary principle is already followed for CNTs [
7] (in the precautionary argument), but at the same time (ii) dismisses it as irrelevant considering the rich availability of information about CNT properties [
18]. There is thus an ambivalent view on the precautionary principle and precautionary regulation in the contra-substitution camp. On the contrary, in the pro-substitution camp, precautionary logic is frequently reiterated: uncertainty must according to them not be an excuse to delay regulatory intervention. They argue that prioritizing scientific certainty before regulatory intervention can incentivize unfortunate substitutions [
13]. Producers might then switch to less studied or newer—and thus not yet regulated—substances, even if these are equally or more hazardous to humans and the environment.
6
Good Science
The relationship between science and regulation is unsettled in the debate. Science is clearly useful or instrumental to develop and ultimately practice regulations that protect humans and the environment from toxic pollutants. This view is shared by the two camps. However, to the contra-substitution camp, quality science, presented as experimental scientific research (mostly nanotoxicology) and performed in a robust manner—precise and standardized—is a value to maintain, in and of itself. Science is therefore articulated as a virtue, in the sense of virtue ethics. The key phrase underlining this value, “scientifically unjustified”, is shared in the titles by two of the responses to the SIN listing: Fadeel and Kostarelos [
18] and Heller et al. [
7].
A science-forward perspective, imbued across the contra-substitution camp and especially evident in the case-by-case and lack of standardization arguments, hinges upon a linear trajectory from good science, producing fundamental certainty, to best regulatory practice. For CNTs that cannot currently be easily grouped through reviewing scientific studies, and where hazards remain unclear and speculative, then hard regulation and demands for substitution are consequently premature. Further, regulatory norms—like high-level grouping—that challenge scientific knowledge or ignore either the unstudied variants or inconclusive work on CNT hazards, should be questioned. The right thing to do is to regulate based on the principle of good science in areas of certainty, which implies that only that which is scientifically well-studied is an appropriate regulatory object.
The pro-substitution camp suggests that because of uncertainty, empirical indications of hazards for some CNTs should be generalized to the rest. CNTs must exist as one aggregated regulatory object for practical purposes to ensure feasibility (as in the regulatory feasibility argument). Regulations should prioritize feasibility in order to safeguard humans and the environment. The burden of proof is then dissimilarity for prospective CNT producers and importers. The contra-substitution camp, on the other hand, starts from the position that the best policy is the most scientifically justified route. According to them, the current scientific evidence suggests that CNTs as a group vary widely [
7,
9,
18]. The burden of proof should thus be similarity. Policy-making should prioritize the science over ease of practical implementation. The best policy is not to group CNTs together
ex ante, but to group at a sub-type level according to empirical evidence.
This value schism between the pro- and contra-substitution camps is thus about priority. The general question remains value-laden: should scientific rigor or regulatory feasibility be the determinant? Here, it can be noted that grouping and precaution are presented as alternative approaches to good science in recent European regulatory research [
4], which assumes both ignorance and practical constraints for nanomaterial innovators. This adds external support to the regulatory feasibility argument through extending these norms into research and innovation, contesting the contra-substitution camp’s unilateral invocation of good science.
Technological Progress
Technological progress is a central concern for the contra-substitution camp, especially Heller et al. [
7], as voiced in the progress argument. In addition to placing safety and good science as key values at stake in the debate, progress in terms of technological advancement is also seen as in jeopardy. The turn from abstract progress to tangible innovation is highlighted with both the progress and safe-by-design arguments: progress and safety happen through continued investment and prioritization of research and innovation. Safety can be achieved by modifying CNTs as suggested in the safe-by-design argument, but might also be a direct effect of progress, since CNT innovation might benefit sectors such as nanomedicine. Progress is thus understood here as deontological—the duty to advance technologically—coupled with the consequentialist assertion of beneficial applications, a recurring trope from Swierstra and Rip’s [
22] “patterns of moral argumentation.” Instead of a sciento-regulatory divide, progress, and safety are articulated as almost inseparable. Technological progress, as described here, results in safety, and is exemplified by two initially problematic cases of nanoparticles: iron oxide, and silica [
7]. This constitutes a rationale for being cautious when discussing hazards and potential regulation; continued investment is seen as the prime mover of both progress and safety. CNTs, like other emerging technologies, depend upon hype [
22,
60] in order to ensure investment and fuel their progression. Regulation, and even its anticipation, puts this at risk.
This processual understanding of progress and safety pivots from the regulatory focus on hazard towards evaluations of risk, echoing elements of the longstanding debate about the role of hazard contra risk in regulation [
61]. There are two positions, risk-predominant and hazard-predominant, that differentiate the pro- and contra-substitution camps.
The first position extends from earlier arguments made by the contra-substitution camp. Safety in terms of the safe use of CNTs is a process of development. Identifications of hazards—the inertia behind the debate—ought to signal substantive development of (i) safe CNTs by less hazardous formulations and (ii) safe use through lessened exposure and thus reduced actual risk. Heller et al. [
7] write that neglecting risk for hazard across emerging technology regulation could threaten the linear progress paradigm: from hype to investment to innovation to safety. Without the safety-through-progress rationale, any emerging technology could struggle to secure funding, as hazards are often inherent to early research and development phases (cf. [
4]). Even if CNTs would be cleared for widespread safe use in the end, it might not be relevant after this supposed initial stigmatization by ChemSec.
The second position, made by the pro-substitution camp, is aligned with the European norm of hazard identification first and risk assessment second, implemented through REACH [
62]. With the hazard identification behind the SIN listing, the limitation of CNTs becomes the mantra, instead of cautious development to eliminate the hazard or minimize exposure. CNT use after hazard identification can, at least according to the weaker variant of the pro-substitution thesis, be tolerated only under exceptional circumstances and not encouraged to achieve progress. Progress can then be redefined as pursuing substances or nanomaterials which, Hansen and Lennquist [
13] conclude, “[…] provide similar functionalities with less risk.”
Conclusion
The researchers from the two camps arrive at different conclusions regarding the core question of the debate: should CNTs be substituted? The debate is indeed devoted to technical issues, with references to experimental studies about CNT carcinogenicity, reproductive toxicity, persistence, and other properties. It can thus appear as if the substitution of CNTs is solely a technical issue, and that its resolution requires further accumulation of data in delaying intervention in favor of stable knowledge (cf. [
9]). However, despite citing similar sets of experimental evidence and shared conceptual understandings, the two camps reach opposing conclusions. This study shows that beyond matters of fact, the technical is indeed exposed as normative in contesting critical assumptions that motivate these dueling positions [
22]. The regulation of CNTs—as problematized in the debate—does not only have ethical implications, but is itself an ethical issue [
21].
The debate is not so much presented as a contest between intrinsic values, but on the optimal means to safeguard them. The value of environmental protection and human safety is shared by both camps, but the instrumental means of safeguarding that value are disputed. The pro-substitution camp favors the substitution of all CNTs based on evidence of hazard for some CNTs, as their preferred means to safety. The contra-substitution camp instead believes that CNTs should be made safe through research and innovation and substituted only on a case-by-case basis given sufficient scientific evidence. The value of good science is advocated by the contra-substitution camp as an intrinsic value to challenge the pro-substitution camp’s prioritization of regulatory norms. Yet, good science is additionally presented as a prerequisite, a means, for environmental protection and human safety through the production of certainty.
In deciding on the future of CNTs, this ethical ambivalence adds to the case for compromise over consensus, of arena behind agora [
22], in resolving the debate. At present, CNTs remain on the SIN list, but not as a Substance of Very High Concern under REACH. Substantive closure remains to be seen, with both ChemSec’s decision made [
13,
17] and
Nature Nanotechnology’s editorial recourse to scientific certainty [
9] functioning as two dueling “temporary stabilizations” [
22]. Put together, this marks an impasse for the debate, underlining the limits to a consensus-oriented, agora model.
Currently, there are at least five areas of future research that can build on the approach elaborated upon in this paper. First, the arena model above suggests a broader power analysis of these conflicting interests—both central and marginal—through stakeholder analysis [
63] that captures CNT governance beyond academia and regulators. Second, this expert debate has implications for the public as well, with a need to investigate their perceptions of CNTs, risk, and toxicity [
28,
35]. Third, while exposing a few inconsistencies, this methodology stops short of normative prescriptions for CNT regulation, a task for additional applied ethics research [
51]. Fourth, similar studies that interrogate anticipatory practices, like the SIN list [
29], could further establish the makings of promissory nanotechnologies in context, as is forthcoming with a follow-up on the institutional position of ChemSec [
64]. Fifth, with the current proliferation of nano-enabled products [
27], narrative studies could trace the temporalities within Swierstra and Rip’s [
22] postulated “co-evolution of ethics and new technologies.”
Thinking beyond CNTs, it is fruitful to ask not only what and why experts argue, but, more fundamentally, to which and whose ends. As such, the debate over whether to substitute CNTs reanimates the question of whose values come to matter in the regulation of particular emerging technologies.
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