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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Administrative data

Link to relevant study record(s)

Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
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:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 120 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: Growth Rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 120 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: Yield (Biomass) and Growth Rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 3.6 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
other: Growth Rate
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 3.6 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
other: Yield (Biomass) and Growth Rate
Conclusions:
A 72-hour EC50 value of >3.6 mg/L and NOEC of ≥3.6 mg/L have been determined for the effects of the test substance on yield and growth rate of Pseudokirchneriella subcapitata based on geometric mean measured exposure concentrations of the test substance. The test substance is known to hydrolyse rapidly in water and 3.6 mg/L was the concentration measured in the highest nominal test concentration of 120 mg/L. It is therefore likely that the test organisms were predominantly exposed to the hydrolysis products of the substance.

Description of key information

ErC50 (72 h) > 120 mg/L (nominal, OECD 201, R. subcapitata; read-across CAS No. 1185-55-3), equivalent to 83 mg/L when expressed in terms of the silanol hydrolysis product methylsilanetriol


 


NOErC (72 h) ≥ 120 mg/L (nominal, OECD 201, R. subcapitata; read-across CAS No. 1185-55-3), equivalent to 83 mg/L when expressed in terms of the silanol hydrolysis product methylsilanetriol

Key value for chemical safety assessment

EC50 for freshwater algae:
83 mg/L
EC10 or NOEC for freshwater algae:
83 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 aquatic algae, 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 201 and in compliance with GLP.


 


In a static test, R. subcapitata were exposed to 5 concentration levels up to 120 mg/L (nominal) for 72 h. Test concentrations were prepared by direct application to test medium. No vehicle was used. Test concentrations were analytically monitored by GC-MS at test start and test end.


 


After 72 h, an ErC50 (72 h) of > 3.6 mg/L (measured), corresponding to > 120 mg/L (nominal) as well as a NOErC (72 h) of ≥ 3.6 mg/L (measured), corresponding to ≥ 120 mg/L (nominal) were determined.


 


In view of the fast hydrolysis rate of the substance and the applied methodology (i.e. test design, test medium preparation) it is likely that the test organisms were predominantly exposed to the hydrolysis products of the tested substance. This is reflected in the low measured concentrations of the parent substance. Effect concentrations are therefore reported in terms of the nominal concentration.


 


The results may be expressed in terms of the silanol hydrolysis product methylsilanetriol (CAS No. 2445-53-6; EC No. 219-489-9), by application of a correction factor for molecular weight (MW of silanol = 94.14 / MW of parent = 136.22), resulting in ≥ 83 mg/L (based on nominal) and > 2.5 mg/L (based on measured concentration).