Dimethoxymethylsilane

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

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 attached justification for grouping of substances provided in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Description of key information

EC10 (3 h) > 100 mg/L (nominal, OECD 209, activated sludge; read across CAS No. 1185 -55 -3)

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 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 toxicity to microorganisms, 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 209 and in compliance with GLP.

 

In a static test, activated sludge of predominantly domestic sewage was exposed to a limit concentration of 100 mg/L for 3 h. After the exposure period, oxygen consumption was measured and recorded for approximately 10 min.

 

No significant effects on the respiration rate were observed, indicating that the test substance was not toxic to activated sludge bacteria at a loading rate of 100 mg/L, resulting in an EC50 (3 h) and EC10 (3 h) of > 100 mg/L (nominal).