Dichloro(diphenyl)silane

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

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

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. 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 1% in 28d was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Reference 2

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 attached justification for grouping of substances in IUCLID Section 13.

Reason / purpose for cross-reference:

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

Description of key information

Dichloro(diphenyl)silane is not readily biodegradable (1% biodegradation in 28 days) (OECD 310; RA CAS No. 98-13-5)

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater

Additional information

There is no data on ready biodegradability for the target substance dichloro(diphenyl)silane (CAS 80-10-4) available. Therefore, a read across to the analogue substance trichloro(phenyl)silane (CAS 98-13-5) has been applied to support the environmental hazard assessment of dichloro(diphenyl)silane (CAS 80-10-4). The target substance dichloro(diphenyl)silane (CAS 80-10-4) hydrolyses within the timescale of a ready biodegradation test to form diphenylsilanediol and hydrochloric acid (DT50 = 10 sec at pH 7 and 1.5 °C). The read across source substance trichloro(phenyl)silane (CAS 98-13-5) is structurally similar to the target substance and like the target substance hydrolyses rapidly to a silanol, which is structurally similar to the silanol hydrolysis product of the target substance. The second hydrolysis product, hydrochloric acid, is an inorganic substance and thus not susceptible to biodegradation. Details on the read across justification can be found in IUCLID Section 13. 

The available study investigating the biodegradation of the analogue substance trichloro(phenyl)silane (CAS 98-13-5) was conducted according to OECD guideline 310 and under GLP conditions. The inoculum, activated sludge from a sewage treatment plant, was exposed for 60 days to the test substance and biodegradation was calculated based on CO₂evolution. No biodegradation of the substance was recorded after 28 d (1%). Thus, the substance is not readily biodegradable according to the OECD criteria. Based on the results of the analogue substance, the hydrolysis product diphenylsilanediol (CAS 947-42-2) of the target substance dichloro(diphenyl)silane (CAS 80- 10-4) is not expected to be readily biodegradable.

On this basis, the target substance dichloro(diphenyl)silane (CAS 80- 10-4) is not considered readily biodegradable.

Furthermore, a test according to OECD 301 has been comissioned for the target substance and the dossier will be updated with the results after obtaining the final report of this study.