Trichloro(methyl)silane

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

46.6 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

6

Modified dose descriptor starting point:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

46.6 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

6

Modified dose descriptor starting point:

NOAEC

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

10.9 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

Overall assessment factor (AF):

1

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

10.9 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

Overall assessment factor (AF):

1

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.6 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

6

Modified dose descriptor starting point:

NOAEL

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.6 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

6

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

Additional information - workers

Trichloro(methyl)silane hydrolyses very rapidly in moist air and in contact with tissues to form hydrogen chloride (HCl) and methylsilanetriol. Local effects (corrosion) are therefore influenced by the formation of HCl, while systemic effects may occur following exposure to the hydrolysis product.Hydrogen and chloride ions will enter the body’s natural homeostatic processes and will not influence the systemic toxicity of the parent substance.

There are no adequate data regarding the repeated dose toxicity of trichloro(methyl)silane itself, therefore data for the related substance methyltrimethoxysilane (MTMS, CAS 1185-55-3) are used for read-across. The use of read-across is considered appropriate as both substances are rapidly hydrolysed to form methylsilanetriol. MTMS also produces three moles of methanol for each mole of parent substance. However, the formation of methanol following exposure to MTMS is not anticipated to have a significant effect on the findings of repeated dose or reproductive toxicity tests in rats.

Hydrogen chloride (HCl)

An EU long-term inhalation Occupational Exposure Limit (OEL) has been set for HCl as 8 mg/m³(8 h TWA) in Commission Directive2000/39/EC.

The SIDS Initial Assessment Report (SIAR) for HCl describes a systemic NOAEL of 20 ppm from a 90-day repeated dose inhalation study (OECD, 2002). However, since the NOAEL for local effects in the same study was 10 ppm it is considered that the observed effects at 20 ppm were secondary to corrosion and were not indicative of true systemic toxicity.

It is therefore considered appropriate by the author of this dataset to use the existing EU OEL for HCl as the starting point to quantify local DNELs for chlorotrimethylsilane.

Methyltrimethoxysilane

In an oral OECD 422 study with methyltrimethoxysilane (MTMS), Sprague-Dawley rats were dosed for 28/29 days in the toxicity phase of the study. The NOAEL was determined to be50 mg/kg bw/dayas there were various organ weight changes and associated histopathologies in the higher dose groups. These effects were not believed to be caused by the other hydrolysis product, methanol. There is also a reliable 90-day inhalation toxicity study that gave a NOAEC of100 ppm (equivalent to 557 mg/m³).There are no reliable repeated dose toxicity data for the dermal route.

It is considered appropriate to use the NOAELs from the oral OECD 422 and the NOAEC from the 90-day inhalation study on methyltrimethoxysilane as the starting point to quantify systemic DNELs for trichloro(methyl)silane by the dermal and inhalation routes respectively.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.

In the absence of any findings relating to reproductive or developmental endpoints in appropriate screening tests, the critical health effect is considered to be corrosion of skin and the respiratory tract. Trichloro(methyl)silane is not classified as mutagenic, carcinogenic or sensitising.

The DNELs used for risk characterisation are therefore:

DNEL (long-term, inhalation): 10.9 mg/m³

DNEL (long-term, dermal): 6.6 mg/kg/day

Qualitative risk characterisation on the basis of local dermal effects is also required.

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

Additional information - General Population

There are no consumer uses of chlorotrimethylsilane, and no potential for exposure to humans via the environment. It is therefore not necessary to calculate DNEL values for the general population.