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

Biodegradation in water: screening tests

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).