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Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1995
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.4-A (Determination of the "Ready" Biodegradability - Dissolved Organic Carbon (DOC) Die-Away Test)
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Marl-Ost municipal sewage treatment plant.

- Suspended solids concentration: 4.1 g/l
Duration of test (contact time):
28 d
Initial conc.:
16.1 mg/L
Based on:
DOC
Details on study design:
TEST CONDITIONS
- Test temperature: 21.5-21.8 °C

- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 2000 ml conical flasks with loose aluminium foil closure

- Number of culture flasks/concentration: 2 test substance (13.6 mg DOC/l after 3h); 2 inoculum blank; 2 control

SAMPLING
- Sampling frequency: DOC analyses (infrared carbon analyser T 500 (Shimadzu)) were carried out at time 0, 3hours, and day 7, 9, 12, 14, 21, 27 and 28. Duplicate determinations on acidified degassed samples after membrane filtration.
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (DOC removal)
Value:
51
Sampling time:
28 d
Details on results:
The control substance achieved a breakdown rate of >70% (DOC decrease) in 14 days


Table 1: Dissolved organic carbon (DOC) concentration (mg/l) and calculated % biodegradation for inoculum blank, test substance and reference substance

Type of suspension

0 h

3 h

7d

9d

12d

14d

21d

27d

28d

DOC (mg/l)

(%) biodeg

DOC (mg/l)

 (%) biodeg

DOC (mg/l)

 (%) biodeg

DOC (mg/l)

 (%) biodeg

DOC (mg/l)

 (%) biodeg

DOC (mg/l)

(%) biodeg

DOC (mg/l)

(%) biodeg

DOC (mg/l)

(%) biodeg

DOC (mg/l)

(%) biodeg

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Inoculum Blank (mean of two replicates with duplicate analyses)

0.56

-

0.13

-

0.94

-

0.37

-

0.38

-

0.29

-

0.16

-

0.58

-

0.38

-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Test sample Replicate 1 (mean of two analyses)

14.80

0.00

13.51

0.00

7.76

49.03

7.81

44.39

8.11

42.23

8.05

42.00

7.23

47.16

7.56

47.83

7.02

50.37

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Test sample Replicate 2 (mean of two analyses)

14.08

0.00

14.07

0.00

8.01

49.28

8.08

44.69

8.05

44.98

8.38

41.97

7.18

49.64

7.49

50.43

7.17

51.29

Mean

 

0

0

 

49

 

45

 

44

 

42

 

48

 

49

 

51

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reference substance Replicate 1 (mean of two analyses)

14.71

0.00

13.80

0.00

0.62

102.34

0.34

100.22

0.63

98.17

0.40

99.20

0.62

96.63

1.07

96.42

0.43

99.63

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reference substance Replicate 2 (mean of two analyses)

14.85

0.00

13.87

0.00

0.71

101.67

0.61

98.25

0.43

99.64

0.42

99.05

0.39

98.33

0.57

100.07

0.47

99.34

Mean

 

0

0

 

102

 

99

 

99

 

99

 

97

 

98

 

99

Validity criteria fulfilled:
yes
Remarks:
<20% variation between replicants results; reference substance reached pass level by day 14.
Interpretation of results:
not readily biodegradable
Conclusions:
The test substance attained 51% degradation in 28 days in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Biodegradation in water (screening tests): 51% in 28 days ( DOC), 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:
freshwater

Additional information

There are no ready biodegradation data available for 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, target), therefore good quality data for the analogous substance, 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0, source) have been read across. In contact with water, the target substance hydrolyses moderately rapidly to form 3-(trihydroxysilyl)propanethiol and ethanol. Similarly, the source substance also undergoes rapid hydrolysis within the course of the biodegradation study to produce the same silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol and methanol.

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

3-(Triethoxysilyl)propanethiol (CAS 14814-09-6) and 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0) 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 wider analogue group for the ready biodegradability endpoint consists of substances containing a number of different functional groups but specific read-across is between substances with similar functionality.

The table below presents ready biodegradation data available for substances relevant to 3-(triethoxysilyl)propanethiol.

It is therefore considered valid to read-across the results for 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0) to fill the data gap for the registered substance since both source substance and target substance generate the same silanol hydrolysis product. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13.

Table: Ready biodegradation data available relevant to 3-(triethoxysilyl)propanethiol

CAS

Name

Main code

Readily biodegradable? Yes/no

Result: Biodegradation after 28 day

Guideline

Reliability

Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for

4420-74-0

3-trimethoxysilylpropane-1-thiol

III-20

No

51%

Annex V C4-A

1

1

In the study with 3-(trimethoxysilyl)propane-1-thiol, 51% biodegradation in 28 days was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP. 3-(Trimethoxysiliyl)propane-1 -thiol (CAS 4420-74-0) is expected to hydrolyse within the timescale of the ready biodegradation study (half-life 2.6 h at pH 7 and 20 -25ºC) to 3-(trihydroxysilyl)propanethiol 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, 3-(trihydroxysilyl)propanethiol.

References:

OECD (2004a): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.

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

PFA (2013f). Peter Fisk Associates, Biodegradation Main Analogue Group report, PFA.300.005.007