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Biodegradation in water: screening tests

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Description of key information

Ready biodegradability [3,3'-(1,1,3,3-tetramethyldisiloxane-1,3-diyl)bispropylamine]: Not readily biodegradable.

Ready biodegradability [3-aminopropyldimethysilanol]: Not readily biodegradable.

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 3,3'-(1,1,3,3-tetramethyldisiloxane-1,3-diyl)bispropylamine (CAS 2469-55-8), therefore good quality data for two structurally-related substances, hexamethyldisiloxane (CAS 107-46-0) and 3-aminopropyltriethoxysilane (CAS 919-30-2), have been read across. All three substances hydrolyse in the time scale of a standard 28-day ready biodegradability test and have silanol hydrolysis products related to those of the registration substance.

3,3'-(1,1,3,3-tetramethyldisiloxane-1,3-diyl)bispropylamine hydrolyses to 3-aminopropyldimethysilanol. Hexamethyldisiloxane hydrolyses to trimethylsilanol. 3-Aminopropyltriethoxysilane hydrolyses to 3-aminopropylsilanetriol. 3-Aminopropyltrimethoxysilane also produces ethanol as a by-product. Ethanol is readily biodegradable (OECD 2004).

3,3'-(1,1,3,3-tetramethyldisiloxane-1,3-diyl)bispropylamine and 3-aminopropyltriethoxysilane 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. These source data for read across are informative in respect of the Si-CCCNH3 groups present in the registration substance structure.

Hexamethyldisiloxane (CAS 107-46-0) is in the siloxane analogue group. In general, siloxane substances exhibit no evidence of any significant biodegradation. These source data for read across are informative in respect of the Si-CH3 groups present in the registration substance structure.

It is therefore considered valid to read-across the results for hexamethyldisiloxane (CAS 107-46-0) and 3-aminopropyltrimethoxysilane (CAS 919-30-2) to fill the data gap for the registered substance. The table below presents ready biodegradation data for the identified read-across substances.

Additional information is given in a supporting report (PFA, 2013f) attached in Section 13.

Table: Ready biodegradation data available for read-across substances  

CAS

Name

Readily biodegradable? Yes/no

Result: Biodegradation after 28 days (%)

Guideline

Test type

Klimisch code

Expected % biodegradation assuming only alkoxy/acetoxy parts biodegrade

Expected % biodegradation assuming only silanol side-chain parts biodegrade

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

Study ID Code[2]

919-30-2

3-aminopropyltriethoxysilane

Yes

76%

OECD 306

DOC

1

67

33

9

5.2.161

000107-46-0

Hexamethyldisiloxane

No

2%

OECD 301C

BOD

1

n/a

n/a

2

5.2.088


[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] This is a unique internal ID code which can be used to identify the reference for the study.

 

In the study with hexamethyldisiloxane (CAS 107-46-0), 2% or 20% biodegradation was observed in 28 days (based on O2 consumption and chemical analysis respectively). Hexamethyldisiloxane hydrolyses within the timescale of the ready biodegradation study to trimethylsilanol. The study was conducted according to OECD 301C and is considered reliable. The study is considered to be reliability 1 (reliable without restrictions).

Two studies are available with 3-aminopropyltriethoxysilane (CAS 919-30-2); in the key study, 76% biodegradation was observed in 28 days (based on O2 consumption). 3-Aminopropyltriethoxysilane hydrolyses within the timescale of the ready biodegradation study to 3-aminopropylsilanetriol and ethanol. The biodegradation observed in the studies is mainly attributable to the biodegradation of the ethanol hydrolysis product. Ethanol is readily biodegradable (OECD, 2004). No significant biodegradation is expected for the silanol hydrolysis product 3-aminopropylsilanetriol. The study was conducted according to OECD 306 and is considered reliable. The study is considered to be reliability 1 (reliable without restrictions).

Both studies are used as weight of evidence for the conclusion on ready biodegradability of 3,3'-(1,1,3,3-tetramethyldisiloxane-1,3-diyl)bispropylamine (CAS 2469-55-8) (and its hydrolysis products).

 

References:

OECD (2004): 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