Registration Dossier

Administrative data

Workers - Hazard via inhalation route

Systemic effects

Long term exposure
Value:
0.63 mg/m³
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
2
Modified dose descriptor starting point:
NOAEC
Acute/short term exposure
Value:
0.63 mg/m³
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
2
Modified dose descriptor starting point:
NOAEC

Local effects

Long term exposure
Value:
0.63 mg/m³
Most sensitive endpoint:
irritation (respiratory tract)
DNEL related information
Overall assessment factor (AF):
2
Dose descriptor:
NOAEC
Acute/short term exposure
Value:
0.63 mg/m³
Most sensitive endpoint:
irritation (respiratory tract)
DNEL related information
Overall assessment factor (AF):
2
Dose descriptor starting point:
NOAEC

Workers - Hazard via dermal route

Systemic effects

Long term exposure
Value:
0.17 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Modified dose descriptor starting point:
NOAEL
Acute/short term exposure
Value:
0.17 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
Overall assessment factor (AF):
300
Modified dose descriptor starting point:
NOAEL

Local effects

Long term exposure
Most sensitive endpoint:
skin irritation/corrosion
Acute/short term exposure
Most sensitive endpoint:
skin irritation/corrosion

Workers - Hazard for the eyes

Additional information - workers

Trimethoxysilane is acutely very toxic following inhalation of vapour, and is corrosive to skin. Indications of systemic toxicity were observed in acute studies using the inhalation, oral and dermal routes. In repeat-dose inhalation studies, the respiratory tract was identified as the potential target organ, and no other systemic effects were observed. At high concentrations effects were observed in a number of organs following oral and dermal exposure, including the lungs, kidney, liver, spleen, pancreas, adrenals, and gastrointestinal tract, but it is not possible to determine if these were secondary to irritation or independent systemic effects.

Repeated exposure of rats to trimethoxysilane vapour in a 9-day range finding study resulted in lethal effects at 5 ppm (0.025 mg/l), attributed to respiratory tract injury. The LOAEC in this study was 1 ppm, and the NOEC was 0.2 ppm. The NOAEC in a 28-day inhalation study was 0.5 ppm. No systemic effects were observed. In a subsequent 90-day vapour inhalation study in the rat, there were no effects at the highest dose level tested, 0.5 ppm. The NOAEC for both local effects was therefore 0.5 ppm, and the NOAEC for systemic effects was ≥0.5 ppm.

The choice of such a low exposure concentration for the repeat-dose studies was determined by the need to minimise suffering of the test animals due to severe respiratory tract injury following exposure to vapour. However, the low concentrations used were not suitable to properly assess potential systemic toxicity. The 90-day NOAEC of 0.5 ppm is therefore considered to be the most appropriate starting point to determine local DNEL for both short and long term exposure via the inhalation route. Since a chronic (2-year) study is not available, it is not possible to establish whether a different mode of action may be relevant for longer-term exposures. It is therefore important to include an assessment factor for extrapolation of duration.

No repeated-dose studies are available via the oral and dermal routes, and since the available inhalation studies did not determine a true NOAEC for systemic effects, it is not possible to derive a dermal DNEL by route-to-route extrapolation. Suitable data are not available for the hydrolysis product, silanetriol.

An oral OECD 422 combined repeat-dose and reproductive/developmental toxicity screening test in rats is available for the substance methyltrimethoxysilane (CAS 1185-55-3). This surrogate substance replaces an –H with –CH3. Both analogues have similar physicochemical properties (log Kow0.7 and 0.2 for methyltrimethoxysilane and trimethoxysilane respectively; predicted water solubility 2.9E+04 and 5.4E+04 mg/l, vapour pressure >2,000 Pa). At neutral pH, the hydrolysis rate of methyltrimethoxysilane is slower than that of the registered substance, trimethoxysilane (half lives ca. 2 hours and <1 hour respectively), but under low pH conditions in the stomach, both substances hydrolyse very rapidly. It is therefore considered valid to read-across from methyltrimethoxysilane to trimethoxysilane in order to determine a DNEL for systemic effects via the dermal route.

No studies have been conducted with trimethoxysilane for reproductive or developmental toxicity. Since the 90 day inhalation study tested very low concentrations of trimethoxysilane which would be unlikely to lead to manifestation of effects in the reproductive organs, it is appropriate to read-across from the structural analogue, methyltrimethoxysilane, for which there is an oral OECD 422 study as described above. In this study no reproductive or developmental effects were observed up to a dose of 1000 mg/kg bw/day. In addition there is a 90 day inhalation study on methyltrimethoxysilane that did not show any adverse treatment-related effects on the reproductive organs up to an exposure concentration of 8900 mg/m3in rats.

In the absence of any findings relating to reproductive or developmental endpoints in appropriate screening tests, the critical health effect is considered to be repeated dose toxicity. Trimethoxysilane is not classified as mutagenic, carcinogenic or sensitising.

The DNELs used for risk characterisation are therefore:

DNEL (long-term, inhalation): 0.63 mg/m3

DNEL (long-term, dermal): 0.17 mg/kg/day

The documented DNELs are considered adequate for the present REACH risk characterisation. They have been calculated using the current ECHA guideline, including the most conservative assessment factors, and are used for the registration under the regulation 1907/2006 dated June 1st 2007 (REACH) only. They should not be used for other regulatory purposes (e.g., OELs) without further consideration and evaluation.

General Population - Hazard via inhalation route

Systemic effects

Acute/short term exposure
DNEL related information

Local effects

Acute/short term exposure
DNEL related information

General Population - Hazard via dermal route

Systemic effects

Acute/short term exposure
DNEL related information

General Population - Hazard via oral route

Systemic effects

Acute/short term exposure
DNEL related information

General Population - Hazard for the eyes

Additional information - General Population

Exposure of consumers is not applicable for this substance.