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EC number: 288-657-1 | CAS number: 85857-16-5
Biodegradation in water: screening tests
Administrative data
Link to relevant study record(s)
Description of key information
Biodegradation in water (screening tests): 7% and 9% in 28 days (EU Method C.4-C, MITI), read-across from an analogous substance.
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 [2-(perfluorohexyl)ethyl]trimethoxysilane (CAS No: 85857-16-5), therefore good quality data for the analogous/structurally related substance, [2-(perfluorohexyl)ethyl]triethoxysilane (CAS No: 51851-37-7), have been read across. In contact with water, [2-(perfluorohexyl)ethyl]trimethoxysilane (CAS No: 85857-16-5) hydrolyses rapidly to form [2-(perfluorohexyl)ethyl]silanetriol and methanol. The hydrolysis products of [2-(perfluorohexyl)ethyl]triethoxysilane are [2-(perfluorohexyl)ethyl]silanetriol and ethanol.
Ethanol and methanol are readily biodegradable (OECD 2004a and OECD 2004b).
[2-(Perfluorohexyl)ethyl]trimethoxysilane (CAS No: 85857-16-5) and [2-(perfluorohexyl)ethyl]triethoxysilane (CAS No: 51851-37-7) 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 III-17 of highly fluorinated chains. [2-(Perfluorohexyl)ethyl]trimethoxysilane (CAS No: 85857-16-5) and [2-(perfluorohexyl)ethyl]triethoxysilane (CAS No: 51851-37-7) are members of this sub-class.
It is therefore considered valid to read-across the results for [2-(perfluorohexyl)ethyl]triethoxysilane (CAS No: 51851-37-7) to fill the data gap for the submission 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 III-17 of chemicals
CAS |
Name |
Main code |
Readily biodegradable? Yes/no |
Result: Biodegradation after 28 day |
Guideline |
Reliability |
Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for[1] |
51851-37-7 |
[2-(Perfluorohexyl)ethyl]triethoxysilane |
III-17 |
No |
9% |
Annex V C4-C |
1a |
-34 |
51851-37-7 |
[2-(Perfluorohexyl)ethyl]triethoxysilane |
III-17 |
No |
7% |
OECD 301C |
1b |
-36 |
2374-14-3 |
2,4,6 -Trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane |
III-17 |
No |
0% |
OECD 301B |
1a |
0 |
[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.
[1a] study conducted in accordance with relevant test method and in compliance with GLP
[1b] study conducted using a test method that is comparable to a relevant OECD/EU test method and in compliance with GLP
Two reliable ready biodegradation studies are available for [2-(perfluorohexyl)ethyl]triethoxysilane. In the first study (Diefenbach, 1997), a ready biodegradation study was conducted in accordance with EU Method C.4 and in compliance with GLP. A biodegradation value of 9% in 28 days was obtained for [2-(perfluorohexyl)ethyl]triethoxysilane. Similarly, in second study (Omura, 2005), a biodegradation value of 7% DOC removal in 28 days was determined for [2-(perfluorohexyl)ethyl]triethoxysilane using a relevant test method and in compliance with GLP. The results are considered to be reliable and are used as weight of evidence.
The studies are considered to be reliability 1 (reliable without restrictions); the read across of the result is considered to be reliability 2 (reliable with restrictions).
References:
OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.
OECD (2004b): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.
PFA, 2013f, Peter Fisk Associates, Biodegradation Main Analogue Group report, PFA.300.005.007
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