Chlorodimethylvinylsilane

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

26.5 mg/m³

DNEL related information

DNEL derivation method:

other: based on 8-hour IOEL for HCl

Dose descriptor:

other: EU IOEL

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

49.6 mg/m³

DNEL related information

DNEL derivation method:

other: based on 15-min STEL for HCl

Dose descriptor starting point:

other: EU OEL

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

Acute/short term exposure

Hazard assessment conclusion:

high hazard (no threshold derived)

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:

high hazard (no threshold derived)

General Population - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

General Population - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

General Population - Hazard via oral route

Systemic effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:

no hazard identified

Additional information - General Population

The following discussion justifies the use of the conclusion 'no hazard identified' for humans exposed via the environment. Oral exposure is only relevant for the assessment of exposure via the environment as there are no consumer uses of this substance.

Background

Due to the very rapid hydrolysis of chloro(dimethyl)vinylsilane, relevant environmental exposure would not be to the parent substance but to the hydrolysis products, dimethyl(vinyl)silanol and HCl. At environmentally-relevant concentrations, the silicon-containing hydrolysis product would be present predominantly as monomeric silanol.

In general, the assessment of the potential level of human risk via the environment is done by first calculating a Derived-No-Effect-Level (DNEL) for the General Population for the relevant route(s) e.g. oral and in some cases, inhalation.

The route of choice for studies most relevant to exposure via the environment is the oral route, since direct exposure to the general population to chlorosilanes or silanols via air emissions from industrial sites is negligible.

Toxicity data for the silicon-containing hydrolysis product are read across from the related substance trimethylsilanol. However, the doses and concentrations used in the toxicity studies are not relevant for the environmental exposure assessment. This is because silanols undergo condensation reactions at the high concentrations that can occur internally in test animals. This means that what the animals are actually exposed to in toxicity studies is not only the monomer, which would be present in the environment, but the dimer (assuming that the behaviour in the GI tract follows the in vitro chemical behaviour). Therefore any observed effects could be due to exposure to the dimer and would then not be relevant for exposure via the environment, where low concentrations mean that condensation is not significant.

A toxicity study conducted at doses and concentrations low enough to ensure exposure to monomer only, i.e. minimal condensation reactions occurring, would almost certainly not result in any systemic toxicological effects.

Discussion

Chloro(dimethyl)vinylsilane undergoes condensation reactions in solution to give siloxane dimers (1,1,3,3 -tetramethyl-1,3 -divinyldisiloxane, CAS 2627 -95 -4). A dynamic equilibrium is established and under certain conditions an insoluble product is formed. The overall rate and extent of condensation is dependent on nominal loading, temperature, and pH of the system, as well as what else is present in the solution. The condensation reactions of monosilanols may be modelled as an equilibrium between monomer and dimer. The reactions are reversible unless the dimer concentration exceeds its solubility; in this case, the dimer forms a separate phase, driving the equilibrium towards the dimer. For dimethyl(vinyl)silanol, an aqueous solution at 100 mg/l is predicted to contain >99% monomer, with very small amounts of dimer. At loadings above about 250 mg/l the concentration of the dimer of the silanol hydrolysis product is predicted to exceed its solubility, resulting in formation of a separate phase. 

Following dosing by oral gavage, partitioning will occur between the dose vehicle and the aqueous environment in the stomach.

Mass dosed                                           =            Body weight (in kg) x dose level (in mg/kg bw day)

 

Dose Concentration                               =           mass dosed/volume

 

This represents an upper limit of the concentration as some of the substance is expected to adsorb to fatty tissue or remain dissolved in the dose vehicle (until this is broken down).

For a study conducted at a dose level of 10 mg/kg bw/day and assuming a body weight of 300 g, the total amount dosed is therefore 3 mg, into an estimated aqueous volume of 1.5 ml in the rat stomach. The concentration in water is therefore up to 2000 mg/l. At such a concentration, condensation is already an important factor.

Body weight                          =            300 g     =            0.3 kg

Total amount dosed                =            3 mg

Estimated aqueous volume    =            1.5 ml

Dose concentration                =            2000 mg/l

 

At a typical upper dose level of 1000 mg/kg bw/day the corresponding concentration would be up to 200 000 mg/l.

Body weight                                           =            300 g      =            0.3 kg

Total amount dosed                               =            300 mg

Estimated aqueous volume    =            1.5 ml

Dose concentration                =            200 000 mg/l

 

Based on a condensation limit of 250 mg/l, the maximum dose level that could be used in practice to ensure exposure mainly to monomeric [dimethyl(vinyl)silanol] is approximately 1.25 mg/kg bw/day or less.

Body weight                                           =            300 g     =            0.3 kg

Total amount dosed                               =            0.375 mg

Estimated aqueous volume    =            1.5 ml

Dose concentration                =            250 mg/l

 

Therefore, any in vivo study relevant to MvE would have to be conducted at doses that would not result in any useful toxicological information and as such would not be ethical to conduct from an animal usage perspective. This ethical point has been confirmed by third parties in the recent consultations required for the trichlorosilane legal action (Case No. A-017 -2015).

Conclusion

In conclusion, it can be demonstrated that testing for the assessment of chloro(dimethyl)vinylsilane via the environment is neither ethical nor technically feasible. In REACH terms it can therefore be concluded that there is no hazard identified for humans via the environment.