This report covers UK REACH dossier and substance evaluation activity undertaken by HSE as the Agency for UK REACH, supported by the Environment Agency for the assessment of environmental information.
Dossier evaluation
Dossier evaluation in UK REACH includes 2 activities, the:
- assessment of Annex 9 or Annex 10 testing proposals submitted by registrants
- compliance checking of registration dossiers
These activities are described under Article 40 and 41 of UK REACH, respectively.
A registrant who intends to generate information to meet any of the requirements set out in Annexes 9 or 10 must submit a testing proposal to HSE. In line with UK REACH Article 40, HSE, supported by the Environment Agency, examines all testing proposals to ensure that they address the statutory information needs and avoid unnecessary testing that would involve the use of vertebrates.
The registrant may only proceed with testing when HSE has issued a formal decision to request the proposed test, a modification of the proposed test, or a different test. The test(s) proposed by a registrant can also be rejected entirely.
HSE, supported by the Environment Agency, may examine a registration dossier at any time to verify that the information submitted by registrants is compliant with the legal requirements. This includes consideration of whether adaptations of the standard testing regime comply with the rules set out in Annexes 7 to 10 or Annex 11. The standard information requirements are cumulative and depend on the tonnage band.
Compliance checks
Most of the registration dossiers submitted up to 31 December 2025 contained little data owing to the transitional provisions for data submission that continued to apply to grandfathered registrations and downstream user import notifications. Therefore, HSE’s compliance checks focused on dossiers relating to ‘novel’ substances, that is, those that were not registered under EU REACH before 1 January 2021. These are not subject to the transitional arrangements described above.
In 2025, HSE completed compliance checks on 13 of these registration dossiers. Six of the checks resulted in draft decisions being issued. Checks on a further 19 dossiers were underway at the end of the year with anticipated completion in 2026. A summary and breakdown by tonnage band is presented in Table 1.
| Tonnage (per annum) | Checks concluded without further data requests | Checks concluded with further data requests | Checks in progress at year end |
|---|---|---|---|
| ≥ 1,000 | 0 | 0 | 3 |
| 100 to 1,000 | 0 | 0 | 1 |
| 10 to 100 | 2 | 3 | 4 |
| 1 to 10 | 5 | 3 | 11 |
| Total | 7 | 6 | 19 |
Across the 6 checks resulting in a draft decision, a total of 17 requests for data were made where standard information requirements were not met and/or adaptations were not justified:
- toxicological – 6 requests for:
- serious eye damage/eye irritation (2)
- skin sensitisation (2)
- mutagenicity (2)
- acute toxicity (1)
- ecotoxicological – 11 requests for:
- short-term toxicity testing on invertebrates (3)
- growth inhibition study aquatic plants (3)
- ready biodegradability (1)
- short-term toxicity on fish (2)
- activated sludge respiration inhibition testing (1)
- hydrolysis as a function of pH (1)
The total number of dossiers compliance-checked between 2021 and the end of 2025 is 51 (44% of those in scope) – see Table 2.
| Tonnage (per annum) | Novel substance registrations received | Checks completed | Concluded without further data requests | Concluded with further data requests | % of in-scope registrations checked |
|---|---|---|---|---|---|
| ≥ 1,000 | 6 | 1 | 1 | 0 | 17% |
| 100 to 1,000 | 6 | 2 | 2 | 0 | 33% |
| 10 to 100 | 21 | 8 | 5 | 3 | 38% |
| 1 to 10 | 83 | 40 | 32 | 8 | 48% |
| Total | 116 | 51 | 40 | 11 | 44% |
No requests were made for new vertebrate data in the first instance. All requests required registrants to apply alternative approaches first. Examples of requested alternative approaches included weight of evidence, read-across, computational predictions, in vitro methods, defined approaches and use of existing data on degradants. Where requests were made for tests on animals, these were to be conducted only if the registrants were not able to use the stated alternatives.
Areas of improvement for dossiers in 2025
While undertaking compliance checks in 2025, HSE made the following general observations to help current and future registrants improve the compliance and quality of their registration dossiers. These complement the Recommendations to registrants.
Justify the choice of test item
Registrants should consider whether the registered substance undergoes rapid transformation when choosing test items for aquatic toxicity tests. To ensure exposure to the appropriate substance, the fate and potential toxicity of the degradants/transformation products may need to be considered. Where the test item chosen is not the registered substance, a scientifically valid justification should be provided in IUCLID. Guidance is available on the OECD website (Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures).
Update registration dossiers when new information becomes available
Registrants are reminded of their Article 22 obligation to keep their registration dossiers up to date (Commission Implementing Regulation (EU) 2020/1435 (legislation.gov.uk)).
HSE notes that some dossiers checked in 2025 contained details of preliminary study reports or studies that were still ongoing at the time of registration. In these situations, registrants should include in their dossier the date by which they expect to be in receipt of the final reports and provide an updated dossier containing the new information without undue delay.
Include information to confirm test guideline validity
Registrants should ensure that their study summaries (SS) and robust study summaries (RSS) contain sufficient information to allow HSE to conclude that test guideline validity criteria have been met.
This year, HSE noted the absence of key validity criteria for some studies relating to the information requirements in Annex 7, section:
- 9.1.1 (Short-term toxicity testing on invertebrates)
- 9.1.2 (Growth inhibition study aquatic plants)
- 9.2.1.1 (Ready biodegradability)
Provide the information required by Annex 11 when making adaptations to the standard testing regime
Where a general adaptation is applied in accordance with Annex 11, registrants are required to provide adequate and reliable documentation to support the use of the adaptation and explain how it meets the information requirement.
When a qualitative or quantitative structure-activity relationship ((Q)SAR) is used to adapt the standard testing regime, the preferred way for registrants to provide this information is to complete and attach the following documents to the dossier:
- (Q)SAR model reporting format (QMRF) to document the model used (usually available from the model developer)
- (Q)SAR prediction reporting format (QPRF) to document the prediction (prediction-specific, provided by the (Q)SAR user)
Templates for the above 2 documents can be found in the OECD (Q)SAR Assessment Framework document (in Annexes 1 and 2, respectively). Additional guidance on the use and reporting of (Q)SARs is also available on the ECHA website: QSAR models (this guidance remains generally valid for UK REACH when read in a GB context).
This documentation is important for the registrant to assure themselves and HSE that the model used is appropriate for the substance (for example the substance is within the model’s applicability domain) and that it is suitable for the regulatory purpose; and to allow for the estimate to be easily reproduced.
In 2025, a lack of appropriate documentation was identified in some dossiers that relied on (Q)SAR to meet the information requirement of Annex 7, Section 7.5 (vapour pressure). Where a (Q)SAR estimate is used to fulfil physicochemical information requirements, in addition to the QMRF and QPRF, the dossier should include an explanation for why the appropriate test was not considered feasible.
Apply relevant guidance for nanoform substances
Registrants should consult appropriate guidance when generating or collecting information to register nanoform substances under UK REACH. Specific appendices are available in ECHA guidance documents on how to meet information requirements and conduct chemical safety assessments. Guidance on how to justify the use of hazard data between nanoforms and/or sets of nanoforms, and the non-nanoforms of the same substance, is available from ECHA (Appendix R.6-1 for nanoforms applicable to the Guidance on QSARs and Grouping of Chemicals).
Guidance on grouping and read-across of nanoforms has also been published by the:
Registering enzymes
For registration purposes, enzymes can have similar properties to each other. Registrants are therefore encouraged to consider providing available data from other enzymes in a read-across approach when registering an enzyme (see UK REACH Annex 11). Data access should be indicated in IUCLID.
Respiratory sensitisation is generally recognised as the key health concern for enzymes. Registrants of enzymes should reflect this property in their hazard conclusions and risk characterisation, recognising that it is difficult to identify dose-response relationships or to establish safe thresholds of exposure for respiratory sensitisation. Some enzyme manufacturers and downstream users have taken a semi-quantitative approach to the risk characterisation of enzymes, examples of which are described in ECHA’s:
- Regulatory Management Options Analysis (RMOA) Conclusion document on enzymes (ECHA website)
- Substance Evaluation and Conclusion Report for amylase (ECHA website).
The enzyme industry has developed several guidance documents in collaboration with downstream users’ associations, which should be consulted as appropriate. For more information please see references in ECHA's RMOA Conclusion document on enzymes.
If registrants are not able to identify a suitable Derived Minimal Effect Level (DMEL), a qualitative assessment could be undertaken in accordance with Section E.3.4.3 of the ECHA Guidance on Information Requirements and Chemical Safety Assessment Part E: Risk Characterisation, in which respiratory sensitisers are categorised as high hazard substances.
Include information to support interpretation of ready biodegradability data
Registrants should include sufficient information to demonstrate that the 10-day window criterion has been met when studies conducted to OECD TG 301 conclude that the test item is readily biodegradable.
Testing proposal evaluations
New testing proposal decisions adopted in 2025
HSE received a testing proposal for one substance. This related to a toxicological information requirement. The proposal was the subject of a public consultation to establish if data already existed that could fulfil the information requirement. This was because the study proposed would involve testing on vertebrates. HSE did not receive any responses to the consultation.
Substance name
Reaction products of 2,2'[(1-methylethylidene)bis(4,1-phenyleneoxymethylene)]bisoxirane and Phenol-formaldehyde polymer, oxiranylmethyl ether and Phenol, 4,(1-methylethylidene)bis-, polymer with 2,2' [(1-methylethylidene)bis(4,1-phenyleneoxymethylene)]bis[oxirane] and 2,2', 6,6'-tetrabromo-4,4'-isopropylidenediphenol
This substance does not have either a CAS or EC number.
Testing proposed
Combined in vivo mammalian alkaline comet assay (OECD TG 489) and in vivo erythrocyte micronucleus test (OECD TG 474).
Testing requested in the decision
HSE confirmed that this test was appropriate to investigate the observed in vitro effects and to meet the relevant information requirement. It also supported the principles of the 3Rs (Replacement, Reduction and Refinement of animals in testing) as it combined 2 separate tests into one, which reduced the total number of animals used.
Information evaluated from submissions that addressed testing proposal decisions made in previous years
In 2025, HSE evaluated toxicological data submitted to meet requirements of testing proposal decisions for 2 substances.
(i) 8-Oxa-3,5-dithia-4-stannatetradecanoic acid, 10-ethyl-4,4-dimethyl-7-oxo-, 2-ethylhexyl ester (CAS: 57583-35-4 and EC: 260-829-0)
Testing requested
In vitro mammalian cell gene mutation test using the thymidine kinase gene (OECD TG 490).
The same testing proposal was submitted concurrently to ECHA. In the EU REACH decision, an in vivo mammalian alkaline comet assay (OECD TG 498) was requested.
Submission and assessment
The registrant submitted a robust study summary for an in vivo mammalian alkaline comet assay (OECD TG 489).
The data had been generated for a different regulatory regime (EU REACH). Although the study conducted deviated from HSE’s request, it met the information requirement for which testing was proposed and therefore it was considered acceptable.
(ii) (R)-1-((4-amino-2-bromo-5-fluorophenyl)amino)-3-(benzyloxy)propan-2-ol 4-methylbenzenesulfonate (CAS: 1294504-64-5 and EC: 810-796-9)
Testing requested
Combined in vivo mammalian alkaline comet assay (OECD TG 489) and in vivo erythrocyte micronucleus test (OECD TG 474).
Submission and assessment
The registrant submitted two robust study summaries; one for each aspect of the combined test (OECD TG 474 and OECD TG 489).
The information met the requirements of the decision.
Substance evaluation
No new substance evaluations were initiated in 2025.
Following completion of the evaluation of N-butylbenzenesulphonamide (CAS: 3622-84-2 and EC: 222-823-6) that was initiated in 2023, HSE is preparing a mandatory classification and labelling proposal in accordance with the GB CLP Regulation in 2025. This is because the available data suggested the substance could meet the GB CLP classification criteria for adverse effects on sexual function and fertility. If confirmed, the proposal will undergo public consultation in line with the procedures of Article 37A of GB CLP in due course.
Also in 2025, a draft decision was issued with respect to the ongoing substance evaluation for paraffin waxes and hydrocarbon waxes, chloro (LCCPs) (CAS: 63449-39-8 and EC: 264-150-0), which had been included on the Rolling Action Plan (RAP) in 2022. The draft decision requested information to clarify if the substance meets the UK REACH Annex 13 criteria for being bioaccumulative (B)/very bioaccumulative (vB) and toxic (T). The registrants commented on the draft decision and HSE is in the process of finalising the decision, which will be issued in 2026.