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EC number: 219-863-1 | CAS number: 2554-06-5
Biodegradation in water: screening tests
Administrative data
Link to relevant study record(s)
Description of key information
Biodegradation in water (screening tests):3.7% in 28 days (OECD 310), read-across from a structurally related substance.
Key value for chemical safety assessment
- Biodegradation in water:
- under test conditions no biodegradation observed
- Type of water:
- freshwater
Additional information
There are no ready biodegradation data available for 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (Vi4-D4), therefore good quality data for the structurally-related substance, octamethylcyclotetrasiloxane (D4, CAS 556-67-2), have been read across.
The registration substance has an average purity of >70% 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (Vi4-D4), with <20% 2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane Vi5-D5 (CAS 17704-22-2; Impurity 1) and <10% 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane Vi3-D3 (CAS 3901-77-7; Impurity 2) present as impurities. Read-across studies are in place as supporting studies, to consider the properties of the impurities. Data for Vi5-D5 are read-across from decamethylcyclopentasiloxane (D5; CAS 541-02-6), data for Vi3-D3 are read-across from hexamethyltrisiloxane (D3; CAS 541-05-9).
D4 is a cyclic siloxane chain with four silicon atoms, connected by four oxygen atoms, in which the Si-O bonds are susceptible to hydrolysis. All silicon atoms present are fully substituted with methyl groups. Similarly, Vi4-D4 is a cyclic siloxane chain with four silicon atoms, connected by four oxygen atoms, in which the Si-O bonds are susceptible to hydrolysis. All silicon atoms present are substituted with one methyl group and one vinyl group. D5 and Vi5-D5, and D3 and Vi3-D3 are structurally analogous in the same way.
The source and target substances possess similar physicochemical properties. A comparison of the key physicochemical properties is presented in the table below.
Table: Summary of physicochemical and ecotoxicological properties for the constituents of the registered substance and their surrogate substances.
CAS Number |
2554-06-5 |
556-67-2 |
17704-22-2 |
541-02-6 |
3901-77-7 |
541-05-9 |
Chemical Name |
2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (Vi4-D4) |
Octamethylcyclotetrasiloxane (D4) |
2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane (Impurity 1 (Vi5-D5)) |
Decamethylcyclopentasiloxane (D5) |
2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane (Impurity 2 (Vi3-D3)) |
Hexamethylcyclotrisiloxane (D3) |
Ultimate Si hydrolysis product |
Methylvinylsilanediol |
Dimethylsilanediol |
Methylvinylsilanediol |
Dimethylsilanediol |
Methylvinylsilanediol |
Dimethylsilanediol |
Molecular weight (parent) |
344.66 |
296.62 |
431 |
370.8 |
259 |
223 |
Molecular weight (hydrolysis product) |
104.18 |
92.17 |
104.18 |
92.17 |
104.18 |
92.17 |
log Kow(parent) |
6.47 |
6.49 |
9.0 |
8.07 |
6.7 |
4.4 |
Water sol (parent) |
0.0073 – 0.0088 mg/l at 23°C |
0.056 mg/l |
9.1E-06 mg/l |
0.017 mg/l |
0.13 mg/l |
2 mg/l |
Vapour pressure (parent) |
93.5 Pa |
132 Pa |
0.6 Pa |
33 Pa |
67 Pa |
671 Pa |
Hydrolysis t1/2at pH 7 and 25°C |
approximately 63 hours |
69-144 hours |
1600 hours |
1590 hours |
0.6 hours |
23 minutes |
Vi4-D4 and D4, and Vi5-D5 and D5, are within the Reconsile Siloxane Category 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.
Vi3-D3 and D3 do not fall within the Siloxane Category definition, as the hydrolysis half-life of each substance is less than 1 hour at pH 7 and 25°C. However, biodegradation data available for D3 is in agreement with the hypothesis applied to the Category of “not readily biodegradable”, and it is concluded that read-across of this result to Vi3-D3 is appropriate.
Additional information is given in a supporting report (PFA, 2017) attached in Section 13 of the IUCLID 6 dossier.
The table below presents ready biodegradation data for substances within the Siloxane Category.
Table: Ready biodegradation data for substances within the Siloxane Category
CAS |
Name |
Readily biodegradable? Yes/no |
Result: Biodegradation after 28 day |
Guideline |
Reliability |
107-46-0 |
Hexamethyldisiloxane |
no |
2% |
OECD 301C |
1 |
107-51-7 |
Octamethyltrisiloxane |
no |
-3.7% (i.e. 0) |
OECD 310 |
1 |
540-97-6 |
Dodecamethylcyclohexasiloxane |
No |
0.045% |
OECD 310 |
1 |
541-02-6 |
Decamethylcyclopentasiloxane |
No |
0.14% |
OECD 310 |
1 |
541-05-9 |
Hexamethylcyclotrisiloxane |
No |
0.06% |
OECD 310 |
1 |
556-67-2 |
Octamethylcyclotetrasiloxane |
No |
3.7% |
OECD 310 |
1 |
1873-88-7 |
1,1,1,3,5,5,5-heptamethyltrisiloxane |
No |
0% |
OECD 310/ ISO Guideline No 14593 |
1 |
2627-95-4 |
1,1,3,3-tetramethyl-1,3-divinyldisiloxane |
No |
0% |
OECD 301D |
1 |
17928-28-8 |
1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane |
No |
0% |
OECD 301F |
1 |
17955-88-3 |
1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane |
No |
10 - 32 % after 25 d |
OECD 301B |
1 |
60111-47-9 |
3-[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-3-phenyl-1,5-divinyltrisiloxane |
No |
2.2% |
OECD 301F |
1 |
069304-37-6 |
1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane |
No |
0% (BOD); 100% (GC) |
OECD 301C |
1 |
070940-00-0 |
1,1,7,7,-Tetramethyl-3,3,5,5,-Tetraphenyl-Tetrasiloxane |
No |
9.7 and 9.9% |
OECD 301B |
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 |
1 |
352230-22-9 |
Siloxanes and Silicones, di-Ph, Ph (trimethylsilyl)oxy |
No |
0% |
OECD 301F |
1 |
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