Dichloro(methyl)silane

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

4.1 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

150

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

4.1 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

150

Modified dose descriptor starting point:

NOAEC

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

12.6 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:

12.6 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:

1.2 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

300

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

1.2 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

Additional information - workers

Dichloro(methyl)silane hydrolyses very rapidly in moist air and in contact with tissues to form hydrogen chloride (HCl) and methylsilanediol. Local effects (corrosion) are therefore influenced by the formation of HCl, while systemic effects may occur following exposure to the silanol 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 dichloro(methyl)silane itself, therefore the properties of the hydrolysis products hydrogen chloride and methylsilanediol are considered appropriate to determine local and systemic DNELs for the parent substance.

No data are available for methylsilanediol, therefore long-term mammalian toxicity data for the closely related structural analogue dimethylsilanediol are used. This surrogate substance replaces an –H with –CH₃. Both analogues have similar physicochemical properties (log K_ow<0; water solubility >1E+06 mg/l; vapour pressure >20,000 Pa). Furthermore, the two parent substances dichloro(methyl)silane and dichloro(dimethyl)silane show similar effects in acute toxicity tests. It is therefore considered valid to read-across from dimethylsilanediol to methylsilanediol, and hence from dichloro(dimethyl)silane to dichloro(methyl)silane.

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 to use the existing EU OEL for HCl as the starting point to quantify local DNELs for dichloro(dimethyl)silane.

Dimethylsilanediol

In an OECD 422 study with dimethylsilanediol, Sprague-Dawley rats were dosed for 28/29 days in the toxicity phase of the study. The NOAEL was determined to be 250 mg/kg/day, based on hepatic protoporphyrinosis in males at the higher dose of 500 mg/kg bw/day. There are no reliable repeated dose toxicity data for the dermal and inhalation routes.

It is considered appropriate to use the NOAELs from the OECD 422 study on dimethylsilanediol as the starting point to quantify systemic DNELs for dichloro(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 repeated dose toxicity. Dichloro(methyl) is not classified as mutagenic, carcinogenic or sensitising.

The DNELs used for risk characterisation are therefore:

DNEL (long-term, inhalation): 4.1 mg/m³

DNEL (long-term, dermal): 1.2 mg/kg/day

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 dichlorodimethylsilane, and no potential for exposure to humans via the environment. It is therefore not necessary to calculate DNEL values for the general population.