Introduction

On 1 January 2026 the long-awaited ‘one substance, one assessment’ (‘OSOA’) legislative package entered into force. It consists of three legislative acts: Regulation (EU) 2025/2457 and Directive (EU) 2025/2456 regarding the relocation of tasks and improving cooperation among Union agencies in the area of chemicals (‘Relocation Measures’), and Regulation (EU) 2025/2455 establishing a common data platform on chemicals (CDP Regulation) – the flagship initiative of the OSOA package. Taken together, the OSOA measures set out to deliver on an overarching ambition: streamlining a fragmented system of chemical safety assessments, which is largely operated by EU scientific agencies. This blogpost discusses the new transparency regime introduced by the OSOA measures, unpacking how it came about, how it operates and what its implications are, in particular for the EU agencies operating in this field. Before turning to that analysis, it briefly sketches out the context against which this transparency regime emerged: the ‘one substance, one assessment’ approach, and the politico-legal dynamics that shaped the OSOA legislation.

From slogan to statute: the ‘one-substance, one assessment’ approach & the role of EU agencies

The slogan ‘one substance, one assessment’ was first coined in the European Commission’s (‘EC’ or ‘Commission’) 2020 Chemicals Strategy for Sustainability (‘Chemicals Strategy’), as shorthand for a more streamlined and coordinated approach to chemical safety assessments across different sectors – in particular (but not only) where the same chemical substance or group of substances must undergo assessment under different regulatory frameworks, according to their intended use (see, for example, benzoic acid which underwent chemical safety assessments under six (!) different frameworks owing to its various applications – from biocides and pesticides to food flavourings, food additives, food contact materials and cosmetics). With the adoption of the OSOA package, the ‘one substance, one assessment’ slogan has finally made the leap from rhetoric to law.

Chemical safety assessments form the scientific foundation of Commission decisions to grant or refuse EU-wide marketing authorisations for chemical substances. While the EC itself also conducts technical or scientific assessments in a few sectors – for example, for non-food consumer products, such as cosmetics or personal care products through the Scientific Committee on Consumer Safety – the main supranational protagonists shaping the science behind chemicals regulation are specialised, independent scientific agencies, namely the European Chemicals Agency (‘ECHA’), the European Food Safety Authority (‘EFSA’), the European Environment Agency (‘EEA’), the European Medicine Agency (‘EMA’) and the European Agency for Safety and Health at Work (‘EU-OSHA’) (hereinafter referred to as ‘scientific agencies’).

After a protracted history of duplicated efforts, inconsistent outputs and varying degrees of transparency, the OSOA laws seek to improve the coherence, efficiency and accessibility of the work carried out by scientific agencies and the relevant Commission configurations charged with scientific or technical tasks (hereinafter collectively referred to as ‘scientific authorities’). Considering the normative weight that the chemical assessments of these scientific authorities carry in the EC’s decision-making on chemicals authorisations in the EU, the re‑ordering and streamlining introduced by this legislation will likely not only affect scientific practice but also future regulatory outcomes.

Situating the ‘one-substance, one-assessment’ legislation: decades of fragmentation and the omnibus surge

2025 was a prolific year for EU legislative activity on chemicals. No less than ten legislative proposals –including the momentous Omnibus proposals on chemicals and food and feed legislation – and six secondary legal acts were adopted that year (among them the much-anticipated OSOA package). What most of these legislative initiatives, including the OSOA measures, have in common is their seemingly moderate aspiration: ‘simplifying’ or ‘streamlining’ the existing Union chemicals acquis. Yet while the framing of the Commission’s Omnibus proposals as simplification efforts has been heavily criticised for obscuring their marked deregulatory imprint (as for the Chemical Omnibus, seethis critical commentary), it would seem misplaced to paint the OSOA package with the same brush.

The simplification narrative underpinning the OSOA legislation is not about embellishing legislative backsliding: these measures aim to genuinely rationalise the work of an increasingly complex, fragmented, and often inefficient ecosystem of actors performing chemical assessments. This is arguably long overdue: studies identifying inconsistencies across different pieces of EU chemicals legislation date back more than a decade. Chemical assessments were found to be duplicated for nearly 10% of the substances placed on the EU market. If a substance-group approach is followed, duplication rates rise to close to 50% for certain groups, such as bisphenols.

Behind these patterns of duplication and inconsistency lie deeper substantive and institutional causes. As for the latter, the Commission pointed to the sheer number of scientific authorities involved in chemical safety assessments, insufficient cooperation and coordination among them, shortcomings in data-sharing and re-use (stemming from differing transparency standards), and the resulting incomplete knowledge base (see Staff Working Documents to the CDP and Relocation Legislation proposals). Insofar as these institutional factors appear closely tied to the incomplete proceduralisation of EU executive rule-making, one might regard them as the concrete symptoms of a malaise long diagnosed by scholars of EU administrative law and the European agentification phenomenon.

Against this backdrop, it seems only reasonable that the EU legislature intervened to strengthen the coherence of chemical assessments through the OSOA laws. In a climate marked by mounting legislative regression under the guise of simplification, the OSOA laws stand out as a positive outlier: rather than rolling back standards, they go to considerable lengths to iron out some of the most pressing structural shortcomings besetting the Union chemicals acquis.

However, there is a notable exception: transparency. Public access to chemicals data is governed by Article 19(2) of the CDP Regulation. As such, it is conditional on the obligation, set out in Article 5(2), requiring all scientific authorities concerned to share their data for integration into the Common Data Platform (‘CDP’). Once included in the CDP, chemical data is not only made accessible to the public but can also be accessed and re-used by all relevant scientific authorities (Article 20), thus feeding back into their scientific work.

Given the entrenched resistance to data-sharingand re-use, the adoption of the CDP Regulation can be considered a real breakthrough towards a common knowledge base on chemicals. Yet it comes at a significant cost for transparency. The next section will elaborate on why that is, uncovering the underlying trade-offs and their impact on the nature and reach of the transparency framework established by the CDP Regulation.

A harmonised transparency framework for chemicals data? Where reality fails ambition

Transparency has arguably been one of the main drivers behind the establishment of the CDP. In the Chemicals Strategy transparency is presented as one of the overarching objectives underpinning the ‘one-substance, one-assessment’ approach (Chemicals Strategy, electronic pages 15-18) and is linked to the ambition to ‘extend the principle of open data and relevant transparency principles from the EU food safety sector to other pieces of chemical legislation’ (Chemicals Strategy, electronic page 18). This signals an intention to harmonise the divergent disclosure requirements across chemicals legislation using the transparency regime governing food safety as a benchmark. Since transparency standards applicable in the food safety domain are the most advanced in EU chemicals policy – and arguably the gold standard for transparent public administration in the EU more broadly – such an approach would imply a significant upward shift in the level of transparency across the wider chemical acquis and relative to other EU policy domains.

The Commission Staff Working Document (SWD) accompanying the CDP proposal published in 2023, mirrors the centrality of transparency first articulated in the Chemicals Strategy: the term ‘transparency’ and its derivatives appear a striking 136 times across 128 pages. Yet, compared with the Chemicals Strategy, a subtle yet important shift crystallised: transparency is no longer framed as a stand-alone aspiration but is tied to data-sharing and re-use arrangements among the various scientific authorities. As the SWD repeatedly notes (SWD, electronic pages 23, 26-27, 59-60, 73), divergent disclosure requirements are considered a key obstacle to the effective transmission and re-use of data across chemicals sectors. A coordinated approach of transparency standards based on the originator principle ‘allows for data sharing between authorities, which is a prerequisite for data use, and as such is considered to indirectly contribute to the efficiency, effectiveness and coherence of chemical safety assessments’ (SWD, electronic page 78).

It is not, in itself, problematic that the alignment of transparency rules is conceived as instrumental to facilitating data sharing and re-use. Quite the contrary: putting in place viable data-sharing and re-use mechanisms is indispensable to realising the ‘one-substance-one assessment’ ideal that underpins the OSAO legislation. What is problematic, however, is that transparency has been subordinated to the logic of data sharing and re-use. The SWD is not explicit on this point, but the related Study on streamlining chemicals data (Chemicals Data Study) is: ‘in view of […] the priority given here to regulatory re-uses, however, a more limited legal approach to the implementation of requirements for improved transparency […] is proposed’.

As a result, the Chemical Strategy’s original ambition of harmonising cross-sectoral transparency standards – taking EFSA’s proactive transparency by-default model as a baseline – was abandoned. The transparency regime reflected in the CDP Regulation (Articles 5(2) and 19(2), CDP Regulation) mirrors the blueprint proposed in Chemical Data Study (Chemicals Data Study, compare electronic pages 27, 30-31, 36, 128, 218-219): a system of dissemination grounded in the originator principle, rather than a uniform transparency framework for chemical safety assessments based on a high level of transparency. This means that data in the CDP is made public according to the transparency rules applicable to the scientific agency from which the data originates. In other words, weak transparency standards, such as those of ECHA, will persist alongside more far-reaching transparency standards, such as those of EFSA. Or, as the Chemicals Strategy did not say: ‘one substance, many transparencies’.

This is a missed opportunity, to say the least: the transparency patchwork underlying EU chemicals governance has been repeatedly criticised in the literature as difficult to justify on functional and normative grounds, as well as for its effects on public perception. Paradoxically, while the Commission appeared to recognise the impact that fragmented transparency rules can have on public sentiment (see SWD, electronic page 21; and CDP proposal, electronic page 10), it nevertheless opted for some form of mutual recognition of transparency standards – a model that preserves divergent regimes instead of delivering genuine harmonisation. That the CDP Regulation still purports ‘to lay down a harmonised framework granting access to the chemicals data contained in the common data platform’ (recital 14, CDP Regulation) is inaccurate at best, and ‘transparency-washing’ at worst.

Under a more troubling scenario, the CDP Regulation could even reduce overall transparency of EU chemicals data by enabling ‘transparency forum shopping’. The scenario goes like this: industry applicants concerned about the economic impact of far-reaching disclosure requirements select a sectoral regime with relatively low transparency standards (e.g., biocides) as their regulatory entry point. Then, leveraging the read-across strategy through enhanced data-sharing and re-use options under the CDP Regulation, they manage to waive a considerable portion of study requirements when submitting an application dossier under a framework with higher transparency standards (e.g., pesticides). In doing so, they effectively evade the stricter transparency obligations applicable under the latter framework for a significant number of scientific studies.

The prohibition for scientific agencies to re-use chemicals data under the CDP with a view to fulfilling the legal requirements of an applicant (Article 20(2), CDP Regulation) does not appear to stand in the way of ‘transparency forum shopping’. After all, in the scenario described above, it is the applicant – not the scientific agency – who re-uses the data to meet the relevant data requirements (in casu, to prepare a scientific justification for data waving based on read-across). The agency merely re-uses chemicals data in the CDP to assess that justification, just as it would assess any other submitted data from the applicant. This falls squarely within the data re-use scenarios that are expressly permitted under Article 20(1) of the CDP Regulation. Much will, of course, depend on scientific agencies interpreting Article 20 of the CDP Regulation in practice. Yet an overly restrictive approach seems unlikely, as it would significantly restrict the scope of one of the Regulation’s core tenets: the facilitation of data re‑use.

Concluding remarks

Perhaps this poor outcome for transparency could have been avoided had the EC relied on more robust evidence when preparing the CDP proposal. The Chemicals Data Study – the central piece of evidence underpinning the chosen transparency model – does not seem to be substantiated by any quantitative data, while its main qualitative input, the stakeholder consultation, was heavily dominated by private interests: 87% of survey responses came from industry, and a clear majority of workshop participants were corporate actors (Chemicals Data Study, electronic pages 142-144).

This speaks to broader structural imbalances in stakeholder representation within EU chemicals policy – both in the legislative process and in regulatory decision-making. Tragically, it is precisely here that progressive transparency standards based on a ‘proactive disclosure by default’ approach could make a difference; transparency is, after all, an important pre-condition for public participation. And proactive transparency, unlike reactive or request-based access to information, does not presuppose that its potential beneficiaries possess particular legal, financial or epistemic resources. Needless to say, when it comes to the CDP Regulation the ideal of stringent proactive transparency was weighed and found wanting. Caught between pressures to safeguard the core features (data-sharing and re-use) of the OSOA approach and the growing pull of deregulatory currents in the EU, the CDP’s curtailed transparency regime reads like a pawn sacrifice – a necessary trade-off to secure agreement on the broader OSOA architecture, propelled by strong business lobbies (and their institutional allies) riding the tides of today’s market-driven (geo-)political dynamics.

About the author

Matthias Hasler is a PhD researcher in EU law at the European University Institute, focusing on the instrumental role(s) of transparency and other tools of participatory democracy in EU chemicals governance. Previously he worked as team lead for pesticides transparency at the European Food Safety Authority.