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Biodegradation in water: screening tests

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Description of key information

Biodegradation in water: screening tests:  76% in 28 days (OECD 306), read-across from an analogous 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
Type of water:
marine water

Additional information

There are no reliable ready biodegradation data available for 3-(trimethoxysilyl)propiononitrile, therefore good quality data for the structurally-related substance, 3-aminopropyltriethoxysilane (CAS 919-30-2), have been read across. Both substances hydrolyse to structurally-related hydrolysis products, 3-(trihydroxysilyl)propiononitrile and 3-aminopropylsilanetriol respectively; the other hydrolysis products are methanol and ethanol respectively.In view of the rapid hydrolysis, it is the silanol hydrolysis product that is relevant for environmental risk assessment.

Ethanol and methanol are readily biodegradable (OECD 2004a and OECD 2004b).

3-(Trimethoxysilyl)propiononitrile (CAS 2526-62-7) and 3-aminopropyltriethoxysilane (CAS 919-30-2) are within a wider analogue group of organosilicon substances that exhibit no evidence of any significant biodegradation once hydrolysis and subsequent biodegradation of alkoxy/acetoxy groups has been taken into account.

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. In this case, however, no data are available for substances containing a nitrile functional group, so data are read across from a substance in a related sub-class of aminofunctional silanes.

The table below presents ready biodegradation data for chlorosilanes, siloxanes, silanes and alkoxysilanes etc. with amino group(s) in side the chain after any very rapid hydrolysis has been accounted for. 3-Aminopropyltriethoxysilane (CAS 919-30-2) is a member of this group of substances.

It is therefore considered valid to read-across the result of not readily biodegradable for 3-aminopropyltriethoxysilane (CAS 919-30-2) 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 relevant substances

CAS

Name

Main code

Readily biodegradable? Yes/no

Result: Biodegradation after 28 days (%)

Guideline

Klimisch code

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

27445-54-1

Cyclohexanamine,N-[(diethoxymethylsilyl)methyl]-

III-08

no

29% (26% taking into account nitrification)

OECD 301F

1

-7

919-30-2

3-aminopropyltriethoxysilane

III-08

No

76%

OECD 306

1

28

31024-56-3

N-[3-(trimethoxysilyl)propyl]butylamine

III-08

No

24.70%

OECD 301B

1

-5

227085-51-0

N-ethyl-3-trimethoxysilyl-2-methylpropanamine

III-08

No

16 - 18%

OECD 301F

1

-15

157923-74-5

2,2-dimethyl-4-(trimethoxysilyl)butylamine

III-08

No

36%

OECD 301F

1

3

3069-33-8

N-[3-(methoxydimethylsilyl)propyl]ethylenediamine

III-08

No

11.10%

OECD 301D

1

-1

1760-24-3

N-(3-(trimethoxysilyl)propyl)ethylenediamine

III-08

No

39%

Annex V C4-A

1

2

82985-35-1

Bis(trimethoxysilylpropyl)amine

III-08

No

11-20%

OECD 301D

2

-33

13497-18-2

Bis(triethoxysilylpropyl)amine

III-08

Yes

64.5% in 28 days, 71% in 60 days

OECD 306

1

-2

[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.

In the study with 3-aminopropyltriethoxysilane (CAS 919-30-2), a biodegradation of 76% in 28 days (M-lab 2005) was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP (OECD 306, Biodegradability in seawater). REACH Guidance R7b states that: When a chemical attains >60% ThOD or >70% DOC removal in a Biodegradability in Seawater test (OECD 306), it can also be expected to fulfil the criteria for ready biodegradability. A biodegradation of 67% in 28 days (not readily biodegradable (Schoerberl 1994) was determined in a second reliable study conducted according to an appropriate test protocol, and in compliance with GLP (EU Method C.4-A).

The result for 3-aminopropyltriethoxysilane is used as weight-of-evidence with a result for the registered substance, which is from a study to which a reliability could not be assigned as only a summary report is available. The result from this study was 61% biodegradation (O2 consumption) in 20 days (BOD test).

3-Aminopropyltriethoxysilane (CAS 919-30-2) hydrolyses within the timescale of the biodegradation study to 3-aminopropylsilanetriol and ethanol. The registered substance hydrolyses within the timescale of biodegradation study to 3-(trihydroxysilyl)propiononitrile and methanol. The biodegradation observed in the studies are attributable to the biodegradation of the ethanol or methanol hydrolysis products.

Ethanol is readily biodegradable (OECD 2004b) and constitutes 67% of the carbons in the test substance, 3-aminopropyltriethoxysilane.

Methanol is readily biodegradable (OECD 2004a) and constitutes 50% of the carbons in the registered substance.

No significant biodegradation is expected for the silanol hydrolysis product.

 

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