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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2009-01-27 to 2009-02-24
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace 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): sewage sludge micro-organisms obtained from the secondary treatment stage of Severn Trent Water Plc treatment plant at Loughborough, Leicestershire, UK. (primarily domestic sewage)

- Preparation of inoculum for exposure: filtered and sparged with CO2

Duration of test (contact time):
28 d
Initial conc.:
32.9 mg/L
Based on:
test mat.
Initial conc.:
20 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
CO2 evolution
Parameter followed for biodegradation estimation:
DOC removal
Remarks:
for blank and reference vessels on day 0 and 28
Details on study design:
TEST CONDITIONS

- Test temperature: 20±1°C

TEST SYSTEM

- Culturing apparatus: 125 ml glass Wheaton bottles sealed with Teflon lined silicon septa and aluminium crimp caps.

- Number of culture flasks/concentration: One hundred and four (104): Innoculum blank: thirty three (33) vessels, test substance: twenty nine (29) vessels, Reference substance: thirty three (33) vessels, Toxicity control: nine (9) vessels

SAMPLING

- Sampling frequency: 0, 2, 6, 8, 14, 16, 21 and 28 days for blank, test and reference substances. Sampling of toxicity control took place on days 0, 8 and 14.

- Sampling method: acidification of the test vessel then sampling of the headspace gas.



CONTROL AND BLANK SYSTEM

- Inoculum blank: yes

- Toxicity control: yes
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (CO2 evolution)
Value:
13
Sampling time:
28 d
Details on results:
Biodegradation of the reference substance was >60% after 14 days (100%) (83% degradation after 28 days).

The toxicity control attained 49% degradation after 14 days.

 Table 1: Total Inorganic Carbon (TIC), % Biodegradation values and Direct Organic Carbon (DOC) values

Day

Inoculum Blank

Reference Substance

Test Substance

Toxicity Control

TIC (mg)

DOC (mg C/l)

TIC (mg)

%Biodeg by TIC

DOC (mg C/l)

% Biodeg by DOC

TIC (mg)

%Biodeg.

TIC (mg)

%Biodeg.

R1

R2

R3

R4

R5

R1

R2

R1

R2

R3

R4

R5

Mean

R1

R2

R1

R2

R1

R2

R3

R4

R5

Mean

R1

R2

R3

Mean

0

0.12

0.10

0.09

-

-

1.24

1.31

0.10

0.10

0.12

-

-

0

20.98

20.97

-

-

0.09

0.10

0.10

-

-

0

0.11

0.12

0.10

0

2

0.13

0.12

0.13

-

-

-

-

1.63

1.67

1.74

-

-

72

-

-

-

-

0.16

0.14

0.15

-

-

1

-

-

-

-

6

0.09

0.16

0.10

-

-

-

-

1.96

1.79

2.02

-

-

84

-

-

-

-

0.14

0.12

0.13

-

-

0

-

-

-

-

8

0.09

0.17

0.10

-

-

-

-

2.08

2.12

2.29

-

-

95

-

-

-

-

0.17

0.14

0.14

-

-

1

2.03

2.11

2.12

46

14

0.11

0.17

0.16

-

-

-

-

2.31

2.38

2.21

-

-

100

-

-

-

-

0.19

0.19

0.17

-

-

1

2.22

2.25

2.26

49

16

0.13

0.13

0.14

-

-

-

-

2.39

2.12

2.20

-

-

99

-

-

-

-

0.21

0.29

0.25

-

-

6

-

-

-

-

21

0.09

0.12

0.14

-

-

-

-

1.98

1.96

1.96

-

-

86

-

-

-

-

0.32

0.33

0.33

-

-

10

-

-

-

-

28

0.12

0.14

0.14

0.16

0.14

1.51

1.01

1.90

1.92

1.88

2.06

1.88

83

1.10

2.12

100

96

0.29

0.43

0.51

0.50

0.52

13

-

-

-

-

Validity criteria fulfilled:
yes
Interpretation of results:
other: under test conditions no significant degradation was observed
Conclusions:
A biodegradation result of 13% in 28 days was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
2009-01-27 to 2009-02-24
Justification for type of information:
Please refer to the attached justification for grouping of substances provided in IUCLID Section 13.
Reason / purpose:
read-across source
Parameter:
% degradation (CO2 evolution)
Value:
13
Sampling time:
28 d

Description of key information

Degradation was 13% in 28 days at 32.9 mg/L concentration of test item (OECD 310), RL1 Biodegradation in water, screening tests: Based on read-across from an analogous substance, no significant biodegradation of the silanol hydrolysis product, (2,4,4-trimethylpentyl)silanetriol, is expected.

Key value for chemical safety assessment

Additional information

There are no reliable ready biodegradation data available for trimethoxy(2,4,4-trimethylpentyl)silane (CAS 34396-03-7), therefore good quality data for the analogous substance, triethoxy(2,4,4-trimethylpentyl)silane (CAS 35435-21-3), have been read across. Both substances share the same hydrolysis product, (2,4,4-trimethylpentyl)silanetriol; the other hydrolysis products being methanol and ethanol, respectively, which are readily biodegradable (OECD, 2004a and b). Both substances are expected to hydrolyse within the timescale of a ready biodegradation test.

Both trimethoxy(2,4,4-trimethylpentyl)silaneandtriethoxy(2,4,4-trimethylpentyl)silane are within a wider analogue group, than the trimethoxysilane analogue group discussed in Section 1.4. Substances within this wider analogue group, in general, exhibit no evidence of any significant biodegradation once hydrolysis and subsequent biodegradation of alkoxy/acetoxy groups has been taken into account.

It is therefore considered valid to read-across the results for triethoxy(2,4,4 trimethylpentyl)silane to fill the data gap for the registered substance.

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.

Table 4.1.4 presents ready biodegradation data available for substances within the sub-class of alkoxysilanes, silanols, acetoxysilanes and chlorosilanes, etc, where the Si part is of low-biological reactivity, once any hydrolysis is accounted for.

 

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

In a test to investigate the biodegradation in water test according to OECD 310 (Harlan, 2009a) activated sludge was exposed to 32.9 mg/l of triethoxy(2,4,4-trimethylpentyl)silane. A biodegradation result of 13% in 28 days based on CO2 evolution was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

This biodegradation is due to the biodegradation of the ethanol hydrolysis product. The methanol hydrolysis product from trimethoxy(2,4,4-trimethylpentyl)silane is also readily biodegradable. No significant biodegradation is expected for the silanol hydrolysis product.

Table 4.1.4 Ready biodegradation data available for substances within the relevant sub-class of chemicals

CAS

Name

Readily biodegradable? Yes/No

Result: Biodegradation after 28 days

Guideline

Reliability

Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for

001066-40-6

Hydroxytrimethylsilane

No

0%

OECD 310

1a

0

018748-98-6

Trimethyl(octadecyloxy)silane

No

68%

OECD 301B

1a

-18

017689-77-9

Triacetoxyethylsilane

Yes

74% in 21 days

EC C4-A

1a

-1

001067-25-0

Trimethoxypropylsilane

No

54%

Annex V C4-A

1a

4

002943-75-1

Triethoxyoctylsilane

No

31.5%

OECD 301D

1a

-11

016415-13-7

Triethoxyhexadecylsilane

No

43%

MITI

1c

16

087135-01-1

1,6-Bis(trimethoxysilyl)hexane

Yes, but not meeting 10-day window

74%

OECD 301B

1a

24

None45

Mixture of 1,1- and 1,2-bis(trimethoxysilyl)ethane

Yes

93%

"Biodegradation study of chemical substances by microorganisms and the like " stipulated in "Testing Method for New Chemical Substances etc.”

1a

18

013154-25-1

Chlorotri(3-methyl-propyl)silane

No

0%

OECD 301B

1a

0

035435-21-3

Triethoxy(2,4,4-trimethylpentyl)silane

No

13%

OECD310

1a

-30

018395-30-7

Trimethoxy(2-methylpropyl)silane

No

36 - 47%

OECD 301B

1a

4

142877-45-0

Silane, trimethoxy(1,1,2-trimethylpropyl)-

No

31%

OECD 301D

1a

-2

017980-47-1

Triethoxyisobutylsilane

Yes

75%

OECD 301D

1a

15

126990-35-0

Dicyclopentyldimethoxysilane

No

12%

OECD 301C

1

-5

139147-73-2

Silane, dichlorodicyclopentyl-

No

0.8%

OECD 301D

2b

1

017865-32-6

Cyclohexyldimethoxymethylsilane

No

15-17%

OECD 301D

1a

-5

None46

t-butoxycyclopentyldimethoxysilane

No

15%

OECD 301C

1a

7

000098-12-4

Cyclohexyltrichlorosilane

No

0%

OECD 301C

1a

0

000124-70-9

Dichloro(methyl)(vinyl)silane

No

-6.78%

OECD 301 A

1a

0

001067-53-4

Tris(2-methoxyethoxy)vinylsilane

Yes

89%

Annex V C4-A

1a

7

002768-02-7

Trimethoxyvinylsilane

No

51%

OECD 301F

1a

-9