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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:
1994-08-31 to 1994-11-02
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)
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
The inoculum employed in the test was activated sludge from the Marl - Ost municipal sewage treatment plant. It was taken off on 1994-09-07 and centrifugated for 15 min at 3000 rpm. The supernatant was rejected and the sludge resuspended with mineral medium (washing). After another centrifugation step 15 min at 3000 rpm, the sludge was resuspended. The content of the dry matter in the inoculum used was 3.45 g/l. The determination of suspended solids was carried out before the inoculum. Dzring this time the sludge had to be aerated by aerating tube. The content of the suspended solids in the test batches was 27.6 mg/l.
Duration of test (contact time):
28 d
Initial conc.:
11.2 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
Vessels: 2000 ml conial flasks with loose aluminium foil closure

Test batches:
2 flasks containing test substance (11.2 mg DOC/l after 3h) and inoculum
2 flasks without test substance, but with inoculum (= blank batch)
2 flasks containing control substance (sodium benzoate: 10.8 mg DOC/l after 3 hours) and inoculum

Method:
Addition of inoculum corresponding a dry matter content of 27.6 mg/test medium.
Filling up with about 2 l mineral medium
30 ml/l test substance stock solution, respectively 20 ml/l control substance stock solution, were given into the test vessels from which the test and control substance batches were filled up.
The content of substances was in mean value 13.33 mg DOC/l (after 3h) in the test batches, respectively 11.28 mg DOC/l (after 3 h) in the control batches.
The batches were filled up to 2.5 l with mineral medium.
From this batches two times 1000 ml were given into 2000 ml Erlenmeyer flasks.
The loosely covered flasks were incubated at 21.9 to 22.2 °C in the dark on a mechanical shaker for 28 days.
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (DOC removal)
Value:
50
Sampling time:
7 d
Key result
Parameter:
% degradation (DOC removal)
Value:
55
Sampling time:
14 d
Key result
Parameter:
% degradation (DOC removal)
Value:
54
Sampling time:
21 d
Key result
Parameter:
% degradation (DOC removal)
Value:
55
Sampling time:
27 d
Key result
Parameter:
% degradation (DOC removal)
Value:
54
Sampling time:
28 d
Details on results:
Results with reference substance:
98% DOC decrease after 7 days
99% DOC decrease after 14 days
100% DOC decrease after 21 days
99% DOC decrease after 27 days
99% DOC decrease after 28 days

DOC measurements of the test item

 

 

DOC concentration after n days (mg/l)

 

Flask no.

 

O h (C0)

3h (C3)

7

14

21

27

28

Test batches

(Mineral

medium +

test item +

inoculum)

1

a1

13.58

13.59

7.53

6.16

6.43

6.78

6.83

a2

13.32

14.13

7.41

6.31

6.43

7.02

6.74

Ca (t) =

(a1 + a2) /2

13.45

13.86

7.47

6.24

6.43

6.90

6.79

2

b1

12.25

13.78

7.04

6.74

6.62

6.28

6.61

b2

12.30

13.38

7.00

6.77

6.67

6.37

6.80

Cb (t) =

(b1+ b2) /2

12.28

13.58

7.02

6.76

6.65

6.33

6.71

Blank batches

(Mineral

medium

+

inoculum)

1

c1

0.52

0.36

0.61

0.50

0.43

0.60

0.62

c2

0.56

0.39

0.54

0.44

0.42

0.65

0.62

Cc (t) =

(c1 + c2) /2

0.54

0.38

0.58

0.47

0.43

0.63

0.62

2

d1

0.49

0.36

0.70

0.53

0.49

0.60

0,62

d2

0.44

0.41

0.68

0.49

0.49

0.61

0.59

Cd (t) 0

(d1 + d2) /2

0.47

0.39

0.69

0.51

0.49

0.61

0.61

 

Cbl(t)=Cc(t)+Cd(t)/2

0.51

0.39

0.64

0.49

0.46

0.62

0.62

 

Validity criteria fulfilled:
yes
Interpretation of results:
other: not readily biodegradable
Conclusions:
A biodegradation result of 54% 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): 0% in 28 days (EU Method C.4-A), read-across from a structurally-related 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 trichloro(propyl)silane (CAS 141-57-1), therefore good quality data for the analogous substance, (trimethoxy(propyl)silane (CAS 1067-25-0), have been read across. Trichloro(propyl)silane hydrolyses very rapidly in contact with water to form propylsilanetriol and hydrochloric acid. The read-across substance, trimethoxy(propyl)silane hydrolyses rapidly in contact with water to form propylsilanetriol and methanol. Both substances hydrolyse rapidly, and extensive or complete hydrolysis in the course of the 28-day ready biodegradation study is to be expected, and both share the same silanol hydrolysis product, propylsilanetriol as stated above. In view of the very rapid hydrolysis, it is the silanol hydrolysis product that is relevant for environmental risk assessment.

 

For trichloro(propyl)silane, biodegradation is not relevant for the non-silanol hydrolysis product, hydrochloric acid being an inorganic substance.

For the read-across substance, trimethoxy(propyl)silane, the non-silanol hydrolysis product, methanol is readily biodegradable (OECD 2004).

Trichloro(propyl)silane (CAS 141-57-1) and trimethoxy(propyl)silane (CAS 1067-25-0) 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 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 for substances relevant to trichloro(propyl)silane.

It is considered valid to read-across the results for trimethoxy(propyl)silane (CAS 1067-25-0) to fill the data gap for the registered substance since the source and target substances generate the same silanol hydrolysis product. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13.

Table 4.1.6: Ready biodegradation data for relevant substances

CAS

Name

Readily biodegradable? Yes/no

Result: Biodegradation after 28 day

Guideline

Test type

Klimisch code

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

1066-40-6

Hydroxytrimethylsilane

No

0%

OECD 310 and ISO Guideline N 14593

CO2

1

0

13154-25-1

Chlorotri(3-methyl-propyl)silane

No

0%

OECD 301B

CO2

1

0

124-70-9

Dichloro(methyl)(vinyl)silane

No

-6.78% (0%)

OECD 301 A

DOC

1

0

017689-77-9

Triacetoxyethylsilane

Yes

74% in 21 days

EC C4-A

DOC

1

-1

1067-25-0

Trimethoxypropylsilane

No

54%

Annex V C4-A

DOC

1

4

18395-30-7

Trimethoxy(2-methylpropyl)silane

No

36 - 47%

OECD 301B

CO2

1

4

2768-02-7

Trimethoxyvinylsilane

No

51%

OECD 301F

BOD

1

-9

[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]Stipulated in "Testing Method for New Chemical Substances etc." (Kanhogyo No.5, Yakuhatsu 615, 49Kikyoku No.392, July 13, 1974 )

In the study with trimethoxy(propyl)silane (CAS 1067-25-0), 54% biodegradation was observed in 28 days.

Trimethoxy(propyl)silane (CAS 1067-25-0), hydrolyses within the timescale of the ready biodegradation study to propylsilanetriol and methanol. The biodegradation observed in the study is attributable to the biodegradation of the methanol hydrolysis product.

Methanol is readily biodegradable (OECD, 2004).

No significant biodegradation is expected for the silanol hydrolysis product.

The study was conducted according to EU Method C.4-A and is considered reliable. This is selected as the key study.

References:

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

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