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Environmental fate & pathways

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:
1994-06-08-06 to 1994-07-06
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method C.4-A (Determination of the "Ready" Biodegradability - Dissolved Organic Carbon (DOC) Die-Away Test)
Deviations:
no
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): activated sludge of a predominantly municipal wastewater treatment plant (Marl-east). Taken 08.06.94.

- Preparation of inoculum for exposure: Centrifuge 15 min at 3000 rpm. Supernatant was discarded and the sludge resuspended with mineral medium. Re-centrifugation: 15 min at 3000 rpm. Resuspension of the sludge. The sludge concentration was 3.77g dry weight per liter. The final concentration of the inoculum per flask test was 26.4 mg/l.
Duration of test (contact time):
28 d
Initial conc.:
11.2 mg/L
Based on:
other: COD (theoretical)
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral salts solution, inoculum and test substance.

- Test temperature: temp 21.9 to 22.1°C


TEST SYSTEM
- Culturing apparatus: 2000 ml Erlenmeyer flask with a loose aluminum foil claps.

- Number of culture flasks/concentration: 2

SAMPLING
- Sampling frequency: At time 0 and after 3 hours, and at 7, 14, 21, 27 and 28 day.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes

- Abiotic sterile control: No

- Toxicity control: No
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (DOC removal)
Value:
56
Sampling time:
28 d
Details on results:
Biodegradation of reference substance 96% in 28d.

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

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

 

 

 

 

 

 

 

 

 

 

 

 

 

Inoculum Blank (mean of two replicates with duplicate analyses)

0.76

-

0.75

-

1.16

-

1.01

-

0.17

-

0.97

-

0.63

-

 

 

 

 

 

 

 

 

 

 

 

 

Test sample Replicate 1 (mean of two analyses)

10.57

0.00

10.75

0.00

5.67

54.90

5.82

51.90

5.76

44.10

5.02

59.50

4.98

56.50

 

 

 

 

 

 

 

 

 

 

 

 

Test sample Replicate 2 (mean of two analyses)

10.33

0.00

10.87

0.00

5.36

58.50

5.87

51.98

6.24

40.02

4.85

61.66

5.13

55.53

Mean

 

0.00

0.00

56.70

 

51.94

 

42.06

 

60.58

 

56.02

 

 

 

 

 

 

 

 

 

 

 

 

Reference substance Replicate 1 (mean of two analyses)

11.77

0.00

11.89

0.00

1.46

97.31

1.04

99.73

0.17

100.00

1.12

98.65

0.99

96.77

 

 

 

 

 

 

 

 

 

 

 

 

Reference substance Replicate 2 (mean of two analyses)

11.65

0.00

11.37

0.00

1.56

96.23

1.02

99.91

0.16

100.09

0.98

99.91

1.05

96.05

Mean

 

0.00

0.00

96.77

 

99.82

 

100.05

 

99.28

 

96.41

 

Validity criteria fulfilled:
yes
Conclusions:
A biodegradation rate of 56 % in 28 days was determined 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:  56% in 28 days (EU Method C.4-A), 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 reliable ready biodegradation data available for 3-chloropropyl(dimethoxy)methylsilane, therefore good quality data for the analogous substance, 3-chloropropyl(diethoxy)methylsilane (CAS 13501-76-3) have been read across. Both substances share the same silanol hydrolysis product, 3-chloropropyl(methyl)silanediol; the other hydrolysis products being 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-Chloropropyl(dimethoxy)methylsilane and 3-chloropropyl(diethoxy)methylsilane are within a wider analogue groupof 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.

The table below presents ready biodegradation data available for chlorosilanes, siloxanes, silanes and alkoxysilanes etc, with chloroalkyl functional group(s) in side chain after any very rapid hydrolysis has been accounted for. 3-chloropropyl(dimethoxy)methylsilane and 3-chloropropyl(diethoxy)methylsilane are members of this group of substances.

It is therefore considered valid to read-across the resultof not readily biodegradablefor 3-chloropropyl(diethoxy)methylsilane 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

Readily biodegradable? Yes/no

Result: Biodegradation after 28 day

Guideline

Reliability

Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for

2212-11-5

Silane, (chloromethyl)dimethoxymethyl-

No

30-34%

OECD 301F

1

-16

7787-93-1

Dichloro(3-chloropropyl)methylsilane

No

0%

EC C4-C

1

0

13501-76-3

3 -Chloropropyl(diethoxy)methylsilane

No

56%

EC C4-A

1

6

2530-87-2

3 -Chloropropyl(trimethoxy)silane

No

43%

OECD 301 B

1

-7

5089-70-3

3 -Chloropropyl(triethoxy)silane

No

46%

EC C4-C

1

-21

2344-80-1

Chloromethyltrimethylsilane

No

6%

OECD 301D

1

6

[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-chloropropyl(diethoxy)methylsilane (13501-76-3), a biodegradation of 56% in 28 days was determined in a reliable study conductedaccording to an appropriate test protocol, and in compliance with GLP (EU Method C.4-A).This biodegradation is attributable to the biodegradation of the ethanol hydrolysis product. No significant biodegradation is expected for the silanol hydrolysis product.

3-chloropropyl(diethoxy)methylsilane (13501-76-3)hydrolyses within the timescale of the biodegradation study to 3-chloropropyl(methyl)silanediol and ethanol. The biodegradation observed in the study is attributable to the biodegradation of the ethanol hydrolysis product.

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