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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

74 % biodegradation in 21 days; based on RA to triacetoxyethylsilane (CAS 17689 -77 -9)

Hydrolysis product ethanol: readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There are no reliable ready biodegradation data available for triethoxy(methyl)silane, therefore good quality data for the analogue substance, triacetoxyethylsilane (CAS 17689 -77 -9), have been read across. Both substances hydrolyse to structurally-related silanol hydrolysis products, methylsilanetriol and ethylsilanetriol. The other hydrolysis products being ethanol and acetic acid, respectively.

 

Therefore, triethoxymethylsilane hydrolyzes rapidly into ethanol which is readily biodegradable and methylsilanetriol which is not. Both triethoxy(methyl)silane and triacetoxyethylsilane are within an analogue group of substances within which, in general, there is no evidence of any significant biodegradation once biodegradation of alkoxy/acetoxy groups has been taken into account.

 

It is therefore considered valid to read-across the results for triacetoxyethylsilane to fill the data gap for the registered substance. This wider analogue group for the ready biodegradability endpoint consists of a number of sub-classes of substances. However, read-across is carried out between substances with the same sub-class in most cases.

 

Table 4.1.4 presents ready biodegradation data available for substances within the sub-class of alkoxysilanes, silanols, acetoxysilanes and chlorosilanes, etc, where the Si part is of low-biological reactivity, once any hydrolysis has been taken into account. Both trimethoxyoctylsilane and triethoxyoctylsilane are members of this sub-class.

 

Additional information is given in a supporting report (PFA, 2013) attached in Section 13 of the IUCLID dossier.

 

A biodegradation rate of 74% in 21 days (DOC removal) was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP (1995). Triacetoxyethylsilane hydrolyses very rapidly in water, to produce acetic acid, which would biodegrade rapidly (six of the eight carbons in triacetoxyethylsilane are converted to acetic acid in a rapid hydrolysis reaction). The silanol hydrolysis product, ethylsilanetriol, is not expected to biodegrade to any significant extent. The study is considered to be reliability 1 (reliable without restrictions); the read across of the result is considered to be reliability 2 (reliable with restrictions).

Table 4.1.4 Ready biodegradation data available for substances within the relevant sub-class of chemicals.

CAS

Name

Readily biodegradable? Yes/No

Result: Biodegradation after 28 days

Guideline

Reliability

Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for

001066-40-6

Hydroxytrimethylsilane

No

0%

OECD 310

1a

0

018748-98-6

Trimethyl(octadecyloxy)silane

No

68%

OECD 301B

1a

-18

017689-77-9

Triacetoxyethylsilane

Yes

74% in 21 days

EC C4-A

1a

-1

001067-25-0

Trimethoxypropylsilane

No

54%

Annex V C4-A

1a

4

002943-75-1

Triethoxyoctylsilane

No

31.5%

OECD 301D

1a

-11

016415-13-7

Triethoxyhexadecylsilane

No

43%

MITI

1c

16

087135-01-1

1,6-Bis(trimethoxysilyl)hexane

Yes, but not meeting 10-day window

74%

OECD 301B

1a

24

None45

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

Yes

93%

"Biodegradation study of chemical substances by microorganisms and the like " stipulated in "Testing Method for New Chemical Substances etc." ( Kanhogyo No.5, Yakuhatsu 615, 49Kikyoku No.392, July 13, 1974 )

1a

18

013154-25-1

Chlorotri(3-methyl-propyl)silane

No

0%

OECD 301B

1a

0

035435-21-3

Triethoxy(2,4,4-trimethylpentyl)silane

No

13%

OECD310

1a

-30

018395-30-7

Trimethoxy(2-methylpropyl)silane

No

36 - 47%

OECD 301B

1a

4

142877-45-0

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

No

31%

OECD 301D

1a

-2

017980-47-1

Triethoxyisobutylsilane

Yes

75%

OECD 301D

1a

15

126990-35-0

Dicyclopentyldimethoxysilane

No

12%

OECD 301C

1

-5

139147-73-2

Silane, dichlorodicyclopentyl-

No

0.8%

OECD 301D

2b

1

017865-32-6

Cyclohexyldimethoxymethylsilane

No

15-17%

OECD 301D

1a

-5

None46

t-butoxycyclopentyldimethoxysilane

No

15%

OECD 301C

1a

7

000098-12-4

Cyclohexyltrichlorosilane

No

0%

OECD 301C

1a

0

000124-70-9

Dichloro(methyl)(vinyl)silane

No

-6.78%

OECD 301 A

1a

0

001067-53-4

Tris(2-methoxyethoxy)vinylsilane

Yes

89%

Annex V C4-A

1a

7

002768-02-7

Trimethoxyvinylsilane

No

51%

OECD 301F

1a

-9