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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
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:
ISO 14593:1999 (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
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): 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. 1h. 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 min.
- 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 d, confirming that test substance was not toxic to the microorganisms in the study.
Results with reference substance:
Reference substance attained 85% degradation after 14 d.

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:
1% biodegradation after 28 days and 0% after 60 days was determined in a reliable study conducted according to OECD guideline 310, 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
Justification for type of information:
Please refer to the attached justification below and the overall justification for grouping of substances attached in IUCLID Section 13.
Reason / purpose:
read-across source
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.
Results with reference substance:
Reference substance attained 85% degradation after 14 d.
Interpretation of results:
under test conditions no biodegradation observed

Description of key information

Trichloro(4-methylphenyl)silane (CAS 701-35-9) is not readily biodegradable (1% after 28 d and 0% after 60 d, OECD 310) based on read across from CAS 98-13-5.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

Data on the biodegradation of trichloro(4-methylphenyl)silane (CAS 701-35-9) are not available. In accordance with Regulation (EC) No. 1907/2006 Annex XI, 1.5 “Grouping of substances and read across” and in accordance with the read across assessment framework (RAAF, ECHA 2017) a read across from the analogue substance trichloro(phenyl)silane (CAS 98-13-5) has been applied to support the environmental hazard assessment of the substance. Details on the read across justification can be found in the attached justification in the respective target entry and in the overall justification for grouping of substances attached in IUCLID Section 13.

The available study (2009) investigating the biodegradation of the analogue substance trichloro(phenyl)silane (CAS 98-13-5) was conducted according to OECD guideline 310 and GLP standards. The inoculum (domestic activated sludge from a sewage treatment plant) was exposed for 60 days to 740 mg/L test substance and biodegradation was calculated based on CO2 evolution. No biodegradation was observed after 28 or 60 d (1 and 0%, respectively). The toxicity control, run in parallel to the study, attained 40% degradation after 14 days confirming that the test substance was not toxic to microorganisms. In conclusion, the analogue substance is considered as not readily biodegradable.

Based on the results of the analogue substance, the target substance trichloro(4-methylphenyl)silane (CAS 701-35-9) is not assumed to be readily biodegradable.

[Type of water: freshwater]