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ECHA | Request to the Committee for Risk Assessment to review the RAC opinion in relation to the harmonised classification of Silanamine, 1,1,1-trimethyl-N-(trimethylsilyl)-, hydrolysis products with silica

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Background - On 5 December 2019, RAC adopted an opinion on  Silanamine, 1,1,1-trimethyl-N-(trimethylsilyl)-, hydrolysis products with silica; pyrogenic, synthetic amorphous, nano, surface treated silicon dioxide (HMDZ-treated SAS; EC Number 272-697-1).

The dossier submitter (France) had proposed a classification for Specific Target Organ Toxicity Repeated Exposure 2 (STOT RE 2) for effects on the lung by inhalation. RAC, taking into account also a number of additional studies from the open literature and applying a weight of evidence approach, considered that the forms of hydrophobic synthetic amorphous silica (SAS) described in the opinion have an acute inhalation effect in the rat. A key study with SAS-DDS, the results of which RAC considered to be relevant also for HMDZ-treated SAS, gave an LC50 of 0.45 mg/L and led RAC to conclude that the substance should in addition be classified for acute toxicity by inhalation Cat. 2, with an ATE of 0.45 mg/L. During the targeted consultation on the inhalation studies from the open literature, stakeholders had commented that the observed lethality was thought to be due to suffocation caused by the tendency of SAS to agglomerate, and thus a purely physical effect. RAC considered this aspect in the background document to the opinion, but stated that no findings supporting this mechanism had been reported in the studies, and that histopathological examinations point to acute respiratory distress syndrome rather than to suffocation. Following adoption and publication of the RAC opinion, manufacturers of the substance provided an additional study which examines the mechanism for the observed acute toxicity of HMDZ-treated SAS via the inhalation route. In the view of the submitters, the study confirms a physical obstruction of the upper respiratory tract by agglomerated HMDZ-treated SAS as the cause of death by suffocation. They further consider that this effect cannot be extrapolated to the humans and, as a physical effect, does not fulfil the criteria for a classification for acute toxicity via inhalation. The submitted information package comprises a study report from a new GLPcompliant acute toxicity inhalation study, which was performed according to OECD TG 436 but goes beyond existing test guidelines for acute toxicity studies, as well as the existing studies examined by RAC, as it includes detailed characterisation of the exposure atmosphere and histopathological examination of the airways of exposed rats and blood oxygen monitoring. The data package further contains a document considering the human relevance of the effects observed in the inhalation studies with rats and a robust study summary in IUCLID format.


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