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Environmental fate & pathways

Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Please refer to the attached justification for grouping of substances provided in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Parameter:
% degradation (CO2 evolution)
Value:
1
Sampling time:
28 d
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
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
Qualifier:
according to guideline
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 headsoace 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
Parameter:
% degradation (CO2 evolution)
Value:
1
Sampling time:
28 d
Parameter:
% degradation (CO2 evolution)
Value:
0
Sampling time:
60 d
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.
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. The result is considered reliable.

Description of key information

0% in 28 d (OECD 310)

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information

There are no reliable ready biodegradation data available for trimethoxyphenylsilane. Therefore, good quality data for the analogue substance, trichloro(phenyl)silane, have been read across. Both the target and source substances are expected to hydrolyse within the timescale of a ready biodegradation test and share the same silanol hydrolysis product, phenylsilanetriol. The other, alcohol hydrolysis products are methanol (target) and hydrochloric acid (source), respectively.

 

In the study on the source substance, 0% biodegradation was observed in 28 days/60 days. The study was conducted according to OECD guideline 310 and is considered reliable. This is selected as the key study. The other hydrolysis product of the source substance, hydrochloric acid, is inorganic and therefore biodegradation is not relevant. The alcohol hydrolysis product of the target substance, methanol, is readily biodegradable based on the results of standard tests that show 76 – 82% and 95% removal in standard ready tests after 5 and 20 days, respectively.

Thus, there is no evidence of any significant biodegradation of the silanol hydrolysis product phenylsilanetriol. For most organosilicon compounds, little or no degradation is observed in ready biodegradation studies once degradation of any readily biodegradable hydrolysis by-product is accounted for.