Registration Dossier

Administrative data

Description of key information

The key study (BRRC, 1995) for repeated dose toxicity via the inhalation route was similar to OECD 413, except that very low concentrations were used. There were no adverse effects up to the highest dose tested (0.5 ppm). In other similarly reliable studies the NOAECs were 5, 0.5 and 0.2 ppm, with effects observed at 10, 5 and 1 ppm, respectively. Therefore it appears that the NOAEC is approximately 0.5 ppm. However, it does appear that most of the effects are a consequence of the severe local effects on the respiratory tract. There are no reliable data available that investigate the potential for trimethoxysilane to cause systemic toxicity following repeated dermal and inhalation exposure. An oral OECD 422 screening test in rats is available for the substance methyltrimethoxysilane (CAS 1185-55-3), which is structurally related to trimethoxysilane (replacement of –H with –CH3). The NOAEL for systemic effects was determined to be 50 mg/kg/day, based on findings in a number of organs including the liver and thymus gland. 

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion
Dose descriptor:
NOAEL
50 mg/kg bw/day

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Dose descriptor:
NOAEC
2.5 mg/m³

Additional information

Three reliability score 2 studies were available for the inhalation route, one of 90-day duration and the others of 28-days.The most recent of these was the 90-day study and this was selected as the key study. The supporting 28-day studies were in agreement with the key study.

Justification for classification or non-classification

Since the effects observed in the available inhalation studies were a result of the local corrosive effects of trimethoxysilane, there is no proposed classification for systemic effects following repeated exposure.