Trichloro(methyl)silane

Endpoint summary

Description of key information

No data on the repeated dose toxicity of trichloro(methyl)silane are available, therefore data on methyltrimethoxysilane have been read-across. The basis for this read-across is that trichloro(methyl)silane and methyltrimethoxysilane are both rapidly hydrolysed to methylsilanetriol. Exposure to methyltrimethoxysilane (MTMS) was associated with organ weight and/or histomorphological changes in males (liver, thymus, thyroid, duodenum, jejunum, and red blood cell) and females (liver, thyroid, duodenum, jejunum, and adrenal gland) at dose levels at or above 250 mg/kg bw/day.  A marked increase in prothrombin time was observed for males at 250 and 1000 mg/kg bw/day whereas females were unaffected. Exposure was also associated with increased blood platelet concentration for males and females at 1000 mg/kg bw/day. These data support a NOAEL for the toxicity phase of the study of 50 mg/kg bw/day. However, since trichloro(methyl)silane is corrosive, additional local effects can be expected for this substance. 
There is also a 90-day inhalation study on methyltrimethoxysilane that can be read-across to trichloro(methyl)silane. Based on the increased incidence of grossly observed urinary bladder  calculi along with the kidney dilation at the 400 ppm exposure level, the  No Observable Adverse Effect Level (NOAEL) for methyltrimethoxysilane  vapor administered six hours per day, five days per week for a 90-day  interval via whole-body inhalation exposure to male and female  Sprague-Dawley rats, was 100 ppm (equivalent to 557.14 mg/m3) . However, since trichloro(methyl)silane is corrosive, additional local effects can be expected for this substance. 

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

557.14 mg/m³

Additional information

No data on the oral repeated dose toxicity of trichloro(methyl)silane are available, therefore data on methyltrimethoxysilane have been read-across.

Methyltrimethoxysilane (MTMS) hydrolyses to give methylsilanetriol (which is also the hydrolysis product of trichloro(methyl)silane) and methanol. For the oral route, a NOAEL of 500 mg/kg was determined for methanol in a study to which reliability could not be assigned. This was based on fairly minor effects at 2500 mg/kg; there was stated to be increased liver weights, with increased liver enzymes. These liver effects were also observed for MTMS, but in females only, and not the same enzymes. Therefore, from the limited information on oral ingestion of methanol, there is no reason to think that the effects for MTMS were caused by methanol. For the inhalation route, the NOEL for methanol was 0.13 mg/l (10 ppm) based on slight body weight and organ weight changes, but even effects at 1000 ppm were not considered to be toxicologically relevant. Effects for MTMS occurred at doses of 400 ppm and above, and were more significant than those of methanol. Therefore, the effects of MTMS can not be attributed to methanol.

Since the read-across substance is not corrosive, it should be assumed that additional local effects, probably of a corrosive nature, and secondary systemic effects, will be observed with trichloro(methyl)silane.

There is an inhalation study using trichloro(methyl)silane, but being a 14 day study, it is not of sufficient duration for classification decisions.

Justification for classification or non-classification

The available data do not suggest that trichloro(methyl)silane should be classified for effects following repeated exposure.