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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): 54% in 28 days (EC method C.4-A), read-across from a structurally-related substance. No significant biodegradation of the silanol hydrolysis product is expected.

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 trimethoxy(methyl)silane (CAS No. 1185-55-3), therefore good quality data for the structurally-related substance, trimethoxypropylsilane (CAS No. 1067-25-0), have been read across. Both substances have structurally similar silanol hydrolysis products, methylsilanetriol and propylsilanetriol respectively. The other hydrolysis product is methanol in both cases.

Methanol is readily biodegradable (OECD 2004).

Trimethoxy(methyl)silane (CAS No. 1185-55-3) and trimethoxypropylsilane (CAS No. 1067-25-0) 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 with different main codes. 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-T-Me-H of Trimethoxysilanes hydrolysing rapidly at pH 7. Trimethoxy(methyl)silane (CAS No. 1185-55-3) and trimethoxypropylsilane (CAS No. 1067-25-0) are members of this sub-class.

It is therefore considered valid to read-across the results for trimethoxypropylsilane (CAS No. 1067-25-0) to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13.

Table: Ready biodegradation data available for substances within the relevant sub-class

CAS

Name

Readily biodegradable? Yes/no

Result: Biodegradation after 28 days (%)

Guideline

PFA Klimisch code

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

1067-25-0

Trimethoxypropylsilane

No

54%

Annex V C4-A

1

4

87135-01-1

1,6-Bis(trimethoxysilyl)hexane

yes but not meeting 10-day window

74%

OECD 301B

1

24

None45

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

Yes

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

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

1

18

18395-30-7

Trimethoxy(2-methylpropyl)silane

No

36 - 47%

OECD 301B

1

4

2768-02-7

Trimethoxyvinylsilane

No

51%

OECD 301F

1

-9


[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 )

In the study with trimethoxypropylsilane (CAS No. 1067-25-0), 54% biodegradation was observed in 28 days. Trimethoxypropylsilane (CAS No. 1067-25-0) hydrolyses within the timescale of the ready biodegradation study to propylsilanetriol and methanol. The biodegradation observed in the study is attributable to the biodegradation of the methanol hydrolysis product.

No significant biodegradation is expected for the silanol hydrolysis product.

The study was conducted according to standard EC method C.4-a and is considered reliable. This is selected as the key study.

Reference:

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.