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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Biodegradation in water (screening tests): 89% in 28 days (EU Method C.4-A), read-across from a related substance. The silanol hydrolysis product, vinylsilanetriol is not expected to biodegrade to any significant extent. 

Key value for chemical safety assessment

Additional information

Tris(isopropenyloxy)vinylsilane (CAS No: 15332-99-7) hydrolyses within the timescale of the ready biodegradation study (≤6.6 h at pH 7) to vinylsilanetriol and propen-2-ol. The biodegradation observed in the study is attributable to the biodegradation of propen-2-ol (or acetone) hydrolysis product. The hydrolysis of [tris(isopropenyloxy)(vinyl)silane] produces vinylsilanetriol and 3 molecules of propen-2-ol. Propen-2-ol is an enol type structure, which is in equilibrium with its keto tautomer, propanone (commonly called acetone). The equilibrium heavily favours the keto form at room temperature. Therefore, the properties of acetone (as well as vinylsilanetriol) are considered for the chemical safety assessment.

Acetone is readily biodegradable (OECD 1999).

No significant biodegradation is expected for the silanol hydrolysis product, vinylsilanetriol.

There are no reliable ready biodegradation data available for tris(isopropenyloxy)vinylsilane (CAS No: 15332-99-7), therefore good quality data for the analogous substance, tris(2-methoxyethoxy)(vinyl)silane (CAS No: 1067-53-4), have been read across. Both substances hydrolyse rapidly in contact with water and share the same silanol hydrolysis product, vinylsilanetriol. In view of the rapid hydrolysis, it is the silanol hydrolysis product, vinylsilanetriol that is relevant for environmental risk assessment.

The other hydrolysis products are propen-2-ol/acetone for the submission substance and methoxyethanol for the read-across substance.

Tris(isopropenyloxy)vinylsilane (CAS No: 15332-99-7) and tris(2-methoxyethoxy)(vinyl)silane (CAS No: 1067-53-4) are within an analogue group of substances within which, in general, there is no evidence of any significant biodegradation once hydrolysis and subsequent biodegradation of alkoxy/acetoxy groups has been taken into account.

This analogue group for the ready biodegradability endpoint consists of a number of sub-classes of substances (based on structure/functionality) with different main codes (used to represent the different sub-classes). However, read-across is carried out between substances with the same main code in most cases.

The table below presents ready biodegradation data for vinyl substances that are relevant for the submission substance. Tris(isopropenyloxy)vinylsilane (CAS No: 15332-99-7) and tris(2-methoxyethoxy)(vinyl)silane (CAS No: 1067-53-4) are members of this sub-class.

It is therefore considered valid to read-across the results for tris(2-methoxyethoxy)(vinyl)silane (CAS No: 1067-53-4) to fill the data gap for the submission substance. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13 of the IUCLID 5 dossier.

Table: Ready biodegradation data for relevant substances within the relevant sub-class of chemicals

CAS

Name

Main code

Readily biodegradable? Yes/no

Result: Biodegradation after 28 day

Guideline

Reliability

Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for[1]

1067-53-4

Tris(2-methoxyethoxy)vinylsilane

II-2

Yes

89%

Annex V C4-A

1

7

754-05-2

Trimethylvinylsilane

I-1

No

0%

OECD 301C

1

0

124-70-9

Dichloro(methyl)(vinyl)silane

I-2-D-C

No

0%

OECD 301A

1

0

[1]The negative values in this column are where the biodegradation rate observed in the test is less than that expected assuming only alkoxy/acetoxy parts biodegrade. This could be due to low solubility of parent substance or low rates of hydrolysis. These values should in effect be considered as zero.

In the study with tris(2-methoxyethoxy)vinylsilane, 89% biodegradation was observed in 28 days.

Tris(2-methoxyethoxy)vinylsilane (CAS No: 1067-53-4) hydrolyses within the timescale of the ready biodegradation study to vinylsilanetriol and methoxyethanol.The biodegradation observed in the study is attributable to the biodegradation of the methoxyethanol hydrolysis product.

Methoxyethanol is expected to be readily biodegradable. No significant biodegradation is expected for the silanol hydrolysis product.

The study was conducted according to EU Method C.4-A and is considered reliable. This is selected as the key study. The key study is supported by biodegradation of 88% (9.93 mg/l initial test substance concentration) and 62% (20 mg/l initial test substance concentration) in 29 days. The study was conducted according to OECD 301B.

The studies are considered to be reliability 1 (reliable without restrictions); read across of the result is considered to be reliability 2 (reliable with restrictions).

References:

OECD (1999): SIDS Initial Assessment Report (SIAR) for the 9th SIAM, Paris, France, 29 -30 June 1999, Acetone, CAS 67-64-1.

PFA (2013f). Peter Fisk Associates, Biodegradation Main Analogue Group report, PFA.300.005.007