Registration Dossier

Diss Factsheets

Environmental fate & pathways

Biodegradation in water: screening tests

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

Biodegradation in water (screening tests):

Constituent 1 (Vi5-D5): 0.14% in 28 days (OECD 310), read-across from a structurally related substance.

Constituent 2 (Vi4-D4): 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

Additional information

There are no ready biodegradation data available for the registration substance or for the individual constituents of the registration substance. For Constituent 2, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (Vi4-D4), good quality data for the structurally-related substance, octamethylcyclotetrasiloxane (D4, CAS 556-67-2), have been read across; for Constituent 1, 2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane (Vi5-D5; CAS 17704-22-2) data are read-across from decamethylcyclopentasiloxane (D5; CAS 541-02-6),

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 is a cyclic siloxane chain with five silicon atoms, connected by five oxygen atoms, in which the Si-O bonds are susceptible to hydrolysis. All silicon atoms present are fully substituted with methyl groups. Similarly, Vi5-D5 is a cyclic siloxane chain with five silicon atoms, connected by five 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.

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

Chemical Name

Constituent 1 of the registration substance:

2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (Vi4-D4)

Octamethylcyclotetrasiloxane (D4)

Constituent 2 of the registration substance:

2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane (Vi5-D5)

Decamethylcyclopentasiloxane (D5)

Ultimate Si hydrolysis product

Methylvinylsilanediol

Dimethylsilanediol

Methylvinylsilanediol

Dimethylsilanediol

Molecular weight (parent)

344.66

296.62

431

370.8

Molecular weight (hydrolysis product)

104.18

92.17

104.18

92.17

log Kow(parent)

6.47 (meas.)

6.49 (meas.)

9.0 (QSAR)

8.02 (meas.)

Water sol (parent)

0.0073 – 0.0088 mg/l at 23°C (meas.)

0.056 mg/l (meas.)

9.1E-06 mg/l (QSAR)

0.017 mg/l (meas.)

Vapour pressure (parent)

93.5 Pa (meas.)

132 Pa (meas.)

0.6 Pa (QSAR)

33.2 Pa (meas.)

Hydrolysis t1/2at pH 7 and 25°C

approximately 63 hours (QSAR)

69-144 hours (meas.)

1600 hours (QSAR)

1590 hours (meas.)


 

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.

Additional information is given in a supporting report (PFA, 2017at) 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 Category

CAS

Name

Readily biodegradable? Yes/no

Result: Biodegradation after 28 day

Guideline

Reliability

000107-46-0

Hexamethyldisiloxane

no

2%

OECD 301C

1c

000107-51-7

Octamethyltrisiloxane

no

-3.7% (i.e. 0)

OECD 310

1a

000540-97-6

Dodecamethylcyclohexasiloxane

No

0.045%

OECD 310

1a

000541-02-6

Decamethylcyclopentasiloxane

No

0.14%

OECD 310

1a

000541-05-9

Hexamethylcyclotrisiloxane

No

0.06%

OECD 310

1a

000556-67-2

Octamethylcyclotetrasiloxane

No

3.7%

OECD 310

1a

001873-88-7

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

No

0%

OECD 310/ ISO Guidline No 14593

1a

002374-14-3

2,4,6-trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane

No

0.0%

OECD 301B

1a

002627-95-4

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

No

0%

OECD 301D

1a

017928-28-8

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

No

0%

OECD 301F

1a

017955-88-3

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

No

10 - 32 % after 25 d

OECD 301B

1a

060111-47-9

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

No

2.2%

OECD 301F

1a

069304-37-6

1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane

No

0% (BOD); 100% (GC)

OECD 301C

1a

070940-00-0

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

No

9.7 and 9.9%

OECD 301B

1a

180073-46-5

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

No

5.2 and 4.4%

OECD 301B

1a

352230-22-9

Siloxanes and Silicones, di-Ph, Ph (trimethylsilyl)oxy

No

0%

OECD 301F

1a

 

Based on read-across of data for structural analogues to the two constituents of the registration substance, it is concluded that the registration substance is not readily biodegradable. As described above, in the target substances each silicon atom is substituted by one methyl and one vinyl group, whereas in the source substances, the silicon atoms are fully methyl substituted. Studies with other vinyl-substituted siloxane substances within the Category also conclude 'not readily biodegradable'.

PFA (2017at) Siloxane Category Report for Environmental Endpoints, PFA.404.114.001

Categories Display