The substance concerned is a synthetic amorphous silica treated with hexamethyldisilazane to make it water-repellent. According to the judgment, synthetic amorphous silicas, including surface-treated forms, are used in medicinal products, food and cosmetics. Industrially, they serve as reinforcement and thickening agents in elastomers, resins and inks. The substance is also an active substance under the Biocidal Products Regulation.

The classification process began in December 2018 with a proposal from the French National Agency for Food, Environmental and Occupational Health and Safety (ANSES). In December 2019, ECHA’s Committee for Risk Assessment (RAC) recommended classification for specific target organ toxicity after repeated exposure, category 2 (hazard statement H373, lungs, inhalation). Through Delegated Regulation (EU) 2022/692, the Commission added this classification to Annex VI of the CLP Regulation. It did not include the acute inhalation toxicity classification also proposed by RAC, as it considered that new information required further assessment. The General Court dismissed the producer’s action for annulment in November 2024, and the appeal followed in February 2025.

The Court of Justice rejected the appeal’s arguments on the intrinsic properties of the substance, on the significance of the observed lung effects and on the burden of proof. It recalled that a party alleging a manifest error of assessment must first bring evidence that casts doubt on the plausibility of the authority’s assessment, and that this does not reverse the burden of proof. It also found that the General Court had properly examined whether the effects identified by RAC, including hypertrophy, lung injury and tissue remodelling, met the CLP criteria. According to reporting on the ruling, the judgment also confirms that read-across from similar substances is a permissible method in harmonised classification procedures.

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