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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
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)
Qualifier:
according to
Guideline:
other: ISO Guideline No 14593 (Water quality- Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous medium -Method by analysis of inorganic carbon in sealed vessels (CO2 headspace test)
GLP compliance:
yes
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): Secondary treatment stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, UK, which treats predominantly domestic sewage.

- Preparation of inoculum for exposure: Sample effluent filtered through coarse filter paper. Filtrate sparged with CO2-free air for approx. 1hr. Inoculum was allowed to settle for approx. 1 hr prior to removal of an aliquot of the supernatant for use in the test.
Duration of test (contact time):
60 d
Initial conc.:
740 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
TEST CONDITIONS
- Solubilising agent (type and concentration if used): Parent material dispersed directly in culture medium with aid of ultrasonication for approx 60 mins.

- Test temperature: 20 ± 1°C

- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 125 ml glass Wheaton bottles sealed using Teflon lined silicon speta and aliminium crimp caps, each containing 107 ml solution (headspace to liquid ration of 1:2.

- Number of culture flasks/concentration: 60 replicates test substance, 39 replicates reference substance, 60 replicates control, 15 replicates toxicity control

SAMPLING
- Sampling frequency: Determination of CO2 produced on days 0, 2, 7, 10, 14, 21, 28, 35, 42, 49, 60 (0, 2, 7, 10 and 14 for toxicity control). Measurement of DOC on days 0, 21, 35, 42, 49, 60.

- Sampling method: CO2: triplicate control, reference substance and test substance vessels were sacrificed on each sampling. DOC: duplicate vessels per sampling.


CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes.

- Toxicity control: Yes
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (CO2 evolution)
Value:
1
Sampling time:
28 d
Key result
Parameter:
% degradation (CO2 evolution)
Value:
0
Sampling time:
60 d
Key result
Parameter:
% degradation (DOC removal)
Value:
0
Sampling time:
60 d
Details on results:
Toxicity control attained 40% degradation after 14 days, confirming that test substance was not toxic to the microorganisms in the study.
Results with reference substance:
Reference substance attained 85% degradation after 14d.

Table 1: Percent degradation values (CO2 determination)

Type of suspension

% degradation at sampling time (days)

0

2

7

10

14

21

28

35

42

49

60

 

Reference substance

-1

64

79

84

85

79

76

77

73

72

74

 

 

 

 

 

 

Test sample

0

0

0

0

2

1

1

0

0

-1

-1

 

 

 

 

 

 

Toxicity control

0

29

36

36

40

-

-

-

-

-

-

 

 

 

 

 

 

 

 

 

 

 

 

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
A biodegradation rate of 0% in 28d 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 (OECD 310), 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

Additional information

There are no reliable ready biodegradation data available for dichloro(methyl)(phenyl)silane, therefore good quality data for the structurally-related substance, trichloro(phenyl)silane (CAS 98-13-5), have been read across. Both substances hydrolyse to structurally-related hydrolysis products, methylphenylsilanediol and phenylsilanetriol respectively; the other hydrolysis product being hydrochloric acid.

Dichloro(methyl)(phenyl)silane and trichloro(phenyl)silane are within an analogue group of substances which in general, exhibit no evidence of any significant biodegradation once hydrolysis and subsequent biodegradation of alkoxy/acetoxy groups has been taken into account.

Table 4.1.6 presents ready biodegradation data available for relevant analogue substances and the closest available analogue, trichloro(phenyl)silane selected for read-across.

It is therefore considered valid to read-across the results for trichloro(phenyl)silane to fill the data gap for the registered substancesince the source and target substances generate similar silanol hydrolysis products. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13.

Table 4.1.6 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

No CAS. EC no. 410-270-5

3-(3-Chloro-4-fluorophenyl)propyldimethylchlorosilane

No

8%

OECD 301B

1

-12 (i.e. 0)

52301-18-5

Tris[(1-methylethenyl)oxy]phenylsilane

Yes

96%

MITI

1

90

98-13-5

Trichloro(phenyl)silane

No

0% after 60d

OECD 310 and ISO Guideline 14593

1

0

No CAS/ EC no.

p-(trihydroxysilyl)styrene

No

26% BOD; 29% TOC; 100% HPLC

OECD 301C

1

2

166255-23-8

4,6-Bis(Carbonylphenyl)-2(3(Triethoxysilyl)propyl)-1,3-Phenylenbisphenylmethanon

No

5%

OECD 301D

1

-20 (i.e. 0)

17890-10-7

Benzenamine, N-[(dimethoxymethylsilyl)methyl]-

yes, but not meeting 10-day window

59-63%

OECD 301F

1

54

250783-08-5

3-[(4'-acetoxy-3'-methoxyphenyl)propyl]trimethoxysilane

No

30%

OECD 301D

1

13

 

In the study with trichloro(phenyl)silane (CAS 98-13-5), 0% biodegradation was observed in 28 days.

Trichloro(phenyl)silane (CAS 98-13-5), hydrolyses within the timescale of the ready biodegradation study to phenylsilanetriol and hydrochloric acid.

No significant biodegradation is expected for the silanol hydrolysis product.

Biodegradation is not relevant for the non-silanol hydrolysis product, hydrochloric acid being an inorganic substance.

 

Reference:

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