The European Court of Justice (ECJ) has upheld the harmonised classification of silanamine as a Category 2 specific target organ toxicity following repeated exposure (STOT RE 2), dismissing an appeal brought by German chemicals manufacturer Evonik.
The judgment, delivered on 5 November 2026 in Case C-121/25 P, confirms silanamine's classification under the EU's Classification, Labelling and Packaging (CLP) Regulation.
The substance is a hydrophobic, surface-treated form of synthetic amorphous silica (SAS), produced using hexamethyldisilazane (HMDS).
The classification carries the hazard statement H373, indicating that repeated inhalation exposure may cause damage to the lungs.
It was introduced through Commission Delegated Regulation (EU) 2022/692, following an assessment by the European Chemicals Agency's (ECHA) Committee for Risk Assessment (RAC).
Read-across methodology under scrutiny
Evonik challenged the classification on several grounds, including the scientific basis for the assessment, the interpretation of particle-related toxicity and the use of read-across data from comparable silica materials.
Read-across allows regulators to use toxicological information from one substance to help assess another with sufficiently similar structural, physical and chemical properties.
In this case, the RAC considered studies involving silanamine alongside data from another surface-modified silica, SAS-DDS.
The ECJ rejected Evonik's arguments, clarifying that the CLP Regulation permits read-across as part of a wider weight-of-evidence assessment.
It also distinguished between the general rules for assessing repeated-exposure toxicity and the specific read-across provisions that apply when a substance has not been tested for toxicity to the relevant target organ.
Crucially, the court also considered studies involving silanamine itself, so the stricter conditions under the specific read-across provision did not apply.
Implications for chemical classification
The ruling leaves the existing STOT RE 2 classification intact and clarifies how regulators can incorporate evidence from comparable substances into assessments.
Evonik welcomed the clarification, according to Frank Menzel, Vice President, Regulatory Marketing Silica at Evonik's Smart Effects business line.
Greater clarity regarding the application of read-across in CLH proceedings may contribute to more predictable regulatory assessments of modified synthetic amorphous silicas and other particulate substances in the future.
The decision is particularly relevant to manufacturers and suppliers navigating EU chemical compliance, where robust toxicological evidence and the justification of read-across approaches are important to harmonised classification and labelling procedures.
