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Biodegradation in water: screening tests

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Description of key information

Biodegradation in water: screening tests: 2.2% in 28 days (O2 consumption, OECD 301F), based on read-across from a structurally-related substance

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

There are no reliable ready biodegradation data available for tris(trimethylsiloxy)phenylsilane (CAS No. 2116-84-9), therefore good quality data for the structurally-related substance, 3-[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-3-phenyl-1,5-divinyltrisiloxane (CAS No. 60111-47-9), have been read across.

Tris(trimethylsiloxy)phenylsilane (CAS No. 2116-84-9) and 3-[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-3-phenyl-1,5-divinyltrisiloxane (CAS No. 60111-47-9) are structurally-similar substances. They are both branched tetrasiloxanes with a phenyl substituent at the central silicon atom. The difference between them is that the target substance has three methyl groups at each of the terminal silicon atoms, whereas the source substance has two methyl groups and one vinyl group at each of the terminal silicon atoms. It is expected that the substitution of the methyl with vinyl group will not affect the biodegradation result.

Tris(trimethylsiloxy)phenylsilane (CAS No. 2116-84-9) and 3-[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-3-phenyl-1,5-divinyltrisiloxane (CAS No. 60111-47-9) are within an analogue group of substances within which, in general, there is no evidence of any significant biodegradation.

Therefore, in the context of the RAAF, Scenario 6 is considered to apply. The Category hypothesis is that read-across of “not readily biodegradable” between siloxanes is appropriate where data are not available for the substance itself. Additional information is given in a supporting report (PFA, 2017) attached in Section 13.

The table below presents ready biodegradation data for substances within the Siloxane Category.

Table: Ready biodegradation data for substances within the siloxane analogue group of chemicals

CAS

Name

Readily biodegradable? Yes/no

Result: Biodegradation after 28 days (%)

Guideline

Test type

Reliability

107-46-0

Hexamethyldisiloxane

No

2%

OECD 301C

BOD

1

107-51-7

Octamethyltrisiloxane

No

-3.70%

OECD 310

CO2

1

540-97-6

Dodecamethylcyclohexasiloxane

No

4.5%

OECD 310

CO2

1

541-02-6

Decamethylcyclopentasiloxane

No

0.14%

OECD 310

CO2

1

541-05-9

Hexamethylcyclotrisiloxane

No

0.06%

OECD 310

CO2

1

556-67-2

Octamethylcyclotetrasiloxane

No

3.70%

OECD 310

CO2

1

1873-88-7

1,1,1,3,5,5,5-heptamethyltrisiloxane

No

0%

OECD 310/ ISO Guideline No 14593

CO2

1

2627-95-4

1,1,3,3-tetramethyl-1,3-divinyldisiloxane

No

0%

OECD 301D

BOD

1

17928-28-8

1,1,1,3,5,5,5-heptamethyl- 3-[(trimethylsilyl)oxy] trisiloxane

No

0%

OECD 301F

BOD

1

17955-88-3

1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane

No

10 – 32 % after 25 d

OECD 301B

CO2

 1

60111-47-9

3-[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-3-phenyl-1,5-divinyltrisiloxane

No

2.20%

OECD 301F

BOD

1

70940-00-0

1,1,7,7,-Tetramethyl-3,3,5,5,-Tetraphenyl-Tetrasiloxane

No

9.7 and 9.9%

OECD 301B

CO2

 1

180073-46-5

Pentasiloxane, 1,1,9,9-tetramethyl-3,3,5,5,7,7-hexaphenyl-

No

5.2 and 4.4%

OECD 301B

CO2

 1

It is therefore considered valid to read-across the results for3-[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-3-phenyl-1,5-divinyltrisiloxaneto fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2017) attached in Section 13.

3-[(Dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-3-phenyl-1,5-divinyltrisiloxane attained 2.2% biodegradation in 28 days (O2 consumption).