Dimethoxymethylsilane

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Please refer to the analogue approach justification provided in Section 13.

Reason / purpose for cross-reference:

read-across source

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 110 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

>= 110 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 200 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

>= 200 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Conclusions:

A 96-hour LC50 value of >110 mg/L and NOEC of ≥110 mg/L have been determined for the effects of the substance on mortality of Oncorhynchus mykiss. Under the flow-through conditions used in the test it is likely that the test organisms were exposed to a mixture of the parent substance and its hydrolysis products.

Description of key information

LC50 (96 h) > 110 mg/L (arithm. mean measured, OECD 203, O. mykiss; read-across CAS No. 1185-55-3)

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Dose descriptor:

LC50

Remarks:

96 h

Effect concentration:

> 110 mg/L

Additional information

The registered substance dimethoxy(methyl)silane (CAS No. 16881-77-9) hydrolyses rapidly (DT50 = 0.3 h) to the silanol hydrolysis products methylsilanediol and methylsilanetriol and the alcohol hydrolysis product methanol.

The ECHA guidance R.16 states that “for substances where hydrolytic DT50 is less than 12 h, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself” (ECHA, 2016). The TGD (EC2003) and ECHA guidance R.16 (ECHA 2010) also suggests that in case the hydrolysis half-life is less than 12 h, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity.

It is anticipated that the second silanol hydrolysis product, methylsilanetriol, is the final product of the

hydrolysis reactions and is thus considered the relevant assessment entity for the present Chemical Safety Assessment according to REACH.

Thus, the environmental fate assessment as well as the hazard and risk assessment are based on the

hydrolysis products methylsilanetriol and methanol rather than the parent substance.

Methanol is known for its absence of environmental toxicity at the concentrations relevant to this dossier (OECD SIDS, 2004), and is therefore not considered contributory to the overall aquatic toxicity of the substance and thus not relevant for the assessment of aquatic toxicity.

 

For the short-term toxicity to fish, no experimental data are available for the registered substance itself. Therefore, read-across was performed from the structurally similar analogue substance trimethoxy(methyl)silane  (CAS No. 1185-55-3), which hydrolyses within a comparable time frame (DT50 = 2.2 h) to the same silanol hydrolysis product methylsilanetriol, which the target and source substances thus share in common. A detailed read-across justification is provided in IUCLID Section 13.

 

The available read-across study was carried out according to the testing guideline OECD 203 and in compliance with GLP. In a flow-through test, Oncorhynchus mykiss were exposed to 5 concentration levels up to 110 mg/L (nominal) for 96 h. Test solutions were prepared by direct addition of the test article to the test medium. The lower test concentrations were prepared with a vehicle (DMF). Test concentrations were analytically monitored by GC-MS at test start and test end.

 

At test end, an LC50 (96 ) of  > 110 mg/L (measured) corresponding to 200 mg/L (nominal) was determined. Under the flow-through conditions used in the test it is likely that the fish were exposed to a mixture of the parent substance and its hydrolysis products. This is reflected in the nominal versus measured test concentrations.