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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: 0% (-6.78%) degradation in 28 days (OECD Guideline 301A) (read-across)

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 1,2-bis[dichloro(methyl)silyl]ethane (CAS 3353-69-3) therefore good quality data for the structurally-related substance, dichloro(methyl)vinylsilane (CAS 124-70-9), have been read across. Both substances hydrolyse very rapidly, and extensive or complete hydrolysis in the course of the 28-day ready biodegradation study is to be expected. Both bis[dichloro(methyl)silyl]ethane and dichloro(methyl)vinylsilane have structurally similar silanol hydrolysis products: 1,2-bis[dihydroxy(methyl)silyl]ethane and methylvinylsilanediol respectively. In view of the very rapid hydrolysis, it is the silanol hydrolysis product that is relevant for environmental risk assessment.]

For both the registration and read-across substances, the non-Si hydrolysis product is hydrogen chloride. Hydrogen chloride is inorganic and biodegradation is not relevant.

 

1,2-bis[dichloro(methyl)silyl]ethane (CAS 3353-69-3) and dichloro(methyl)vinylsilane (CAS 124-70-9) 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 substances within the sub-class I-2 Non-Functional Organosilanes. 1,2-bis[dichloro(methyl)silyl]ethane (CAS 3353-69-3) and dichloro(methyl)vinylsilane (CAS 124-70-9) are members of this sub-class.

It is therefore considered valid to read-across the results dichloro(methyl)vinylsilane (CAS 124-70-9) to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13 of the IUCLID 6 dossier.

 

Table: Ready biodegradation data for substances within the relevant sub-class I-2 of chemicals

CAS

Name

Main code

Readily biodegradable? Yes/no

Result: Biodegradation after 28 days (%)

Guideline

Test type

Klimisch code

Result: Biodeg (%)

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

013154-25-1

Chlorotri(3-methyl-propyl)silane

I-2-M-C

No

0%

OECD 301B

CO2

1

0

0

139147-73-2

Silane, dichlorodicyclopentyl-

I-2-D-C

No

0.80%

OECD 301D

BOD

2

0.8

1

000098-12-4

Cyclohexyltrichlorosilane

I-2-D-C

No

0%

OECD 301C

BOD

1

0

0

000124-70-9

Dichloro(methyl)(vinyl)silane

I-2-D-C

No

-6.78% (0%)

OECD 301 A

DOC

1

0

0

017865-32-6

Cyclohexyldimethoxymethylsilane

I-2-D-Me-H

No

15-17%

OECD 301D

BOD

1

17

-5

126990-35-0

Dicyclopentyldimethoxysilane

I-2-D-Me-M

No

12%

OECD 301C

BOD

1

12

-5

None46

t-butoxycyclopentyldimethoxysilane

I-2-D-Me-M

No

15% BOD; 25% TOC; 100% GC

OECD 301C

BOD/DOC

1

25

7

017689-77-9

Triacetoxyethylsilane

I-2-T-A

Yes

74% in 21 days

EC C4-A

DOC

1

74

-1

017980-47-1

Triethoxyisobutylsilane

I-2-T-Et-M

Yes

75%

OECD 301D

BOD

1

75

15

002943-75-1

Triethoxyoctylsilane

I-2-T-Et-M

No

31.50%

OECD 301D

BOD

1

31.5

-11

035435-21-3

Triethoxy(2,4,4-trimethylpentyl)silane

I-2-T-Et-M

No

13%

OECD310

CO2

1

13

-30

016415-13-7

Triethoxyhexadecylsilane

I-2-T-Et-S

No

43% by BOD; 74% by HPLC

MITI

BOD

1

43

16

001067-25-0

Trimethoxypropylsilane

I-2-T-Me-H

No

54%

Annex V C4-A

DOC

1

54

4

087135-01-1

1,6-Bis(trimethoxysilyl)hexane

I-2-T-Me-H

yes but not meeting 10-day window

74%

OECD 301B

CO2

1

74

24

None45

Mixture of 1,1- and 1,2-bis(trimethoxysilyl)ethane

I-2-T-Me-H

Yes

93% BOD; 78% TOC; 100% GC (ethanol?)

"Biodegradation study of chemical substances by microorganisms and the like"[2]

BOD/DOC

1

93

18

018395-30-7

Trimethoxy(2-methylpropyl)silane

I-2-T-Me-H

No

36 - 47%

OECD 301B

CO2

1

47

4

002768-02-7

Trimethoxyvinylsilane

I-2-T-Me-H

No

51%

OECD 301F

BOD

1

51

-9

142877-45-0

Silane, trimethoxy(1,1,2-trimethylpropyl)-

I-2-T-Me-S

No

31%

OECD 301D

BOD

1

31

-2

 

In the study with dichloro(methyl)vinylsilane (CAS 124-70-9), 0% biodegradation was observed in 28 days.

dichloro(methyl)vinylsilane (CAS 124-70-9) hydrolyses within the timescale of the ready biodegradation study to methylvinylsilanediol and hydrogen chloride. No significant biodegradation is expected for the silanol hydrolysis product.

The study was conducted according to OECD 301A and is considered reliable. This is selected as the key study.

References:

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

 


[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.

 

[2]Stipulated in "Testing Method for New Chemical Substances etc." (Kanhogyo No.5, Yakuhatsu 615, 49Kikyoku No.392, July 13, 1974 )

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