Dimethoxymethylsilane

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

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

Analytical monitoring:

yes

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

21 d

Dose descriptor:

LOEC

Remarks:

MATC

Effect conc.:

> 10 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

> 10 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality: Number of living offspring produced per surviving parental animal {for Daphnia magna, TG 211}

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

> 10 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality: Number of living offspring produced per surviving parental animal {for Daphnia magna, TG 211}

Executive summary:

A 21 day chronic toxicity study in Daphnia magna with the test substance methylsilanetriol (pre-hydrolysed from the parent substance methyltrimethoxysilane) was conducted according to OECD TG 211 and in compliance with GLP. A 21 day NOEC value of 10 mg/l (mean measured concentration) (highest concentration tested) was determined for the effects of methysilanetriol on reproduction, growth (length) and mortality. Additionally, a LOEC for the same endpoints was determined to be >10 mg/L.

Description of key information

NOEC (21 d) ≥ 10 mg/L (arithm. mean measured, OECD 211, D. magna; read-across hydrolysis product methylsilanetriol CAS No. 2445-53-6)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

NOEC

Remarks:

21 d

Effect concentration:

>= 10 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 long-term toxicity to aquatic invertebrates, 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 211 and in compliance with GLP.

 

In a semi-static limit test, Daphnia magna were exposed to 12 mg/L methylsilanetriol (nominal) for 21 d. The test substance was prepared by direct addition of the parent substance trimethoxy(methyl)silane  (CAS No. 1185-55-3) to dilution water followed by stirring to allow for complete hydrolysis prior to test start. Test solutions were prepared by direct application to test medium. No vehicle was used. The test concentrations were analytically monitored by HPLC-MS at test start and after 2, 7, 14, 19 d and at test end (21 d).

 

After 21 d, no adverse effects were observed and a NOEC (21 d) of ≥ 10 mg/L (arithmetic mean measured) was determined for the effects of the hydrolysis product methylsilanetriol (CAS No. 2445-53-6) in the survival, growth and reproduction of Daphnia magna.