Reaction mass of 4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane and 4,4,14,14-tetraethoxy-3,15-dioxa-8,9,10-trithia-4,14-disilaheptadecane

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:

weight of evidence

Study period:

1996-02-21 to 1996-07-22

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Taunusstein-Bleidenstadt sewage plant

- Storage length: Used on day of preparation

- Preparation of inoculum for exposure: The sample was washed twice with mineral nutrient solution and resuspended in mineral nutrient medium.
The sludge was then aerated for 4 hours with compressed air and homogenized in a household blender at low speed for 2 minutes. The
homogenized sludge was filtered through a cotton filter previously rinsed with deionized water.

- Concentration of sludge: 1% in final test solutions

Duration of test (contact time):

28 d

Initial conc.:

98 - 100 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: ~100 mg test substance incubated with sewage sludge in a mineral medium

- Test temperature: 25 ± 1 °C

- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus: Special incubation vessels of a respirometer

- Number of culture flasks/concentration: Two test substance solutions, two blank solutions, one abiotic control (1st test series only), one reference, one toxicity control (1st test series only)


SAMPLING
- Sampling frequency: Oxygen uptake recorded automatically by the respirometer. Additionally the oxygen uptake was read manually on the display and documented. At the end of the study (after 28d) the COD of the test solutions was determined.

- Sampling method: 20ml of test solution were extracted for COD analysis

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes

- Abiotic sterile control: Yes

- Toxicity control: Yes

Reference substance:

benzoic acid, sodium salt

Test performance:

Three separate tests were conducted. In the first test, using duplicate solutions with a concentration of 96 mg/l, the test substance attained 42% and 9% degradation respectively. There was no oxygen uptake in a test solution with test substance which was poisoned with HgCl2. The toxicity control
showed a slight bacterial inhibition (9.3%).

Since the difference between degradation of replicates was >20% , a second test was conducted. After three weeks, a defect in the cooling device of
the respirometer meant that the study had to be abandoned.

A third test was undertaken using duplicate test vessels containing 98 and 100 mg/l test substance. The difference in degradation between
replicates in this test was 19.2%, thereby fulfilling the validity criterion.

An exact determination of the remaining COD of the test solutions with the test substance at the end of the test was not possible because of the
behaviour of the test substance. The test material was not homogeneously dispersable in the aqueous phase, so there was a discrepancy in COD
values in parallel test mixtures. Higher COD values than were theoretically possible were measured due to the presence of larger particles of test
substance being introduced into the test mixtures for COD determination. The COD determination ot the control substance solutions showed good
correlation with the results obtained with the respirometer.

The oxygen consumption in the inoculum blanks was reported as 0.25 mg/l.

Key result

Parameter:

% degradation (O2 consumption)

Value:

20

Sampling time:

28 d

Details on results:

The reference substance degraded >60% within three days of incubation.

Only the results of the third test series are reported. The first and second test series were invalid.

Table 1: Biological oxygen demand (mgO₂/mg TS) and calculated % degradation for test substance and reference substance over 28 d test

	Time
	1	2	3	4	7	8	9	10	11	14	15	16	17	18	21	22	23	24	25	28
BODTS(mgO2/mg TS) Test substance R1	0	0.008	0.02	0.03	0.07	0.79	0.09	0.11	0.12	0.16	0.18	0.19	0.21	0.23	0.28	0.30	0.33	0.35	0.38	0.44
BODTS(mgO2/mg TS) R2Test substance	0	0.003	0.003	0.003	0.02	0.028	0.04	0.04	0.05	0.06	0.07	0.08	0.08	0.09	0.11	0.12	0.13	0.13	0.14	0.15
% degradation (BOD/COD x 100) Test substance R1	0	0.5	1.2	1.9	4.4	5.3	6.3	7.1	8.0	10.9	12.1	12.9	13.9	15.1	18.7	20.3	21.9	23.3	25.2	29.4
% degradation (BOD/COD x 100) Test substance R2	0	0.2	0.2	0.2	1.5	1.9	2.5	2.9	3.3	4.2	4.7	5.2	5.5	6.0	7.2	8.0	8.5	8.9	9.2	10.2
% degradation Test substance (mean)	0	<1	1	1	3	4	4	5	6	8	8	9	10	11	13	14	15	16	17	20
BODTS(mgO2/mg TS) Reference substance	0.3	0.90	1.27	1.34	1.44	1.47	1.49	1.50	1.51	1.53	1.55	1.55	1.56	1.56	1.59	1.60	1.60	1.60	1.61	1.61
% degradation (BOD/COD x 100) Reference substance	18	54	76	80	87	88	89	90	91	92	93	93	94	94	95	96	96	96	97	97

 

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

A biodegradation rate of 20% in 28 days 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:

experimental study

Adequacy of study:

weight of evidence

Study period:

From 1999-06-15 to 1999-08-18

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Test method of new chemical substance, in Kanpogyo no. 5, Yakuhatsu No. 615 and 49 Kikyoku No. 392 1974

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I))

Version / remarks:

1992

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

mixture of sewage, soil and natural water

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Sites for collection of sludge: collected from 10 sites nationwide in Japan: Fushikokawa sewage, Kashima sewage, Nakahama sewage, Ochiai sewage, Kitakamigawa river, Shinano river, Yoshino river, Lake Biwa, Hiroshima Bay, Doukai Bay. Date March 1999. The sewage sludge collected was returned sludge from sewage treatment plants. The river, lake, sea sludge was surface soil at boundary of beach contacting surface water and atmosphere.

- Mixing of fresh and old activated sludge: 5 L of an activated sludge cultivated for ca. 3 months and 5L of the filtrate of mixture of sludge collected from the above sites were mixed to make 10 L.

- Method of cultivation: Approximately 30 min after stopping the aeration into the cultivating vessel, ca. a 1/3 of total supernatant liquid was removed. De-chlorinated water as added to the vessel to male a total volume of 10 L and the liquid in the vessels was aerated again for more than 30 min. 50 g/L of artificial sewage to 0.1 wt% in the added dechlorinated water. The same procedure was repeated once a day and activated sludge was provided after cultivating. Temperature of the cultivation was set at 25 +/- 2 degC. Artificial sewage consisted of: glucose, peptone and potassium dihydrogen phosphate dissolved in dechlorinated water to adjust the concentration at 50 g/L and sodium hydroxide was added to adjust the pH to 7.0 +/- 1.

- Preparation of inoculum for exposure: Before use, the activation level was checked with a standard substance.

- Concentration of sludge: 30 g/L.

Duration of test (contact time):

28 d

Initial conc.:

100 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS

- Composition of medium: 300 ml of cultivation medium, containing 1.91 ml of activated sludge was poured into test vessels and 30 mg of the test substance was added to the vessels to achieve nominal concentration of 100 mg/L.

- Test temperature: 25 ± 1 degC, measured daily.

- pH: 7

- pH adjusted: yes, culture medium and artificial sewage were adjusted to pH 7.

- Aeration of dilution water: yes

- Suspended solids concentration: 30 mg/L.

- Continuous darkness: not reported


TEST SYSTEM

- Culturing apparatus: 300 ml cultivation vessel (modified type).

- Number of culture flasks/concentration: three for test substance at 100 mg/l; one for reference; one for abiotic control; one for blank

- Test performed in closed vessels due to significant volatility of test substance: yes


SAMPLING

- Sampling frequency: BOD was continuously measured in the vessels. As a result of evidence of the production of ethanol and water soluble silicon in a preliminary test, after the cultivation period quantitative analysis was conducted on the test liquid for residual dissolved organic carbon, test substance, ethanol and water-soluble silicon


CONTROL AND BLANK SYSTEM

- Inoculum blank: Yes

- Abiotic sterile control: Yes

Reference substance:

aniline

Remarks:

Reference value set to exceed 40% and 65%, respectively, of the degradation rate of aniline detemined by BOD on day 7 and 14 respectively.

Key result

Parameter:

% degradation (O2 consumption)

Value:

5

Sampling time:

28 d

Key result

Parameter:

% degradation (test mat. analysis)

Value:

15

Sampling time:

28 d

Details on results:

Degradation calculated by BOD 4%, 6%, 6% - average 5%.
Degradation obtained by HPLC 9%, 22%, 13% - average 15%.
Degradation of reference on Day 7 and 14 determined by BOD was 57% and 77%, respectively.

Table 1. Analytical results.

 

		Water + TS	Sludge + TS			Theoretical value
Vessel		#6	#1	#2	#2
BOD	mg	0.0	2.2	3.7	3.7	58.2
DOC residual amount and rate	mgC	4.4	0.3	0.8	0.6	13.2
	%	33	3	6	4	-
Residual amount of test substance and residual rate (HPLC)	mg	22.2	27.4	23.5	26.0	30.0
	%	74	91	78	87	-
Production of ethanol and production rate (GC)	mg	5.0	0	0	0	17.3
	%	29	0	0	0	-
Production of water-soluble silicon and production rate (AA)	mg	0.6	0.4	0.7	0.6	3.6
	%	16	11	21	17	-
Mass balance of silicon portion	%	90	102	99	104	-

TS is test substance

Where vessel # is: 1, 2 and 3 – sludge + test substance; 4 – control blank; 5 – sludge + Aniline; 6 – water + test substance.

 

Table 2. Percentage of degradation on day 28.

 

	Degradation (%)
	#1	#2	#3	Average
Result by BOD	4	6	6	5
Result by HPLC	9	22	13	15

 

 

Table 3. Percentage BOD in the 28 day test.

 

	Sample days								Mean Deg. (%)
	7		14		21		28
Vessel #	BOD (mg)	Deg. (%)	BOD (mg)	Deg. (%)	BOD (mg)	Deg. (%)	BOD (mg)	Deg. (%)
5	52.3	57	71.7	77	72.1	77	72.2	76
4	0.7	-	1.8	-	2.2	-	3.6	-
1	1.5	1	3.1	2	4.3	4	5.8	4
2	2.0	2	3.7	3	5.6	6	7.3	6
3	2.2	3	3.9	4	5.5	6	7.3	6	5
6	0.0	-	0.0	-	0.0	-	0.0	-

Where vessel # is: 1, 2 and 3 – sludge + test substance; 4 – control blank; 5 – sludge + Aniline; 6 – water + test substance.

Deg is equal to percentage biodegradation.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

A biodegradation rate of 5% (O2 consumption) to 15% (test material analysis) in 28 days 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:

Whole substance: 5% (O₂ consumption) to 15% (test material analysis) degradation in 28 days (OECD 301C) read-across from structurally-related substance reaction mass of S2, S3 and S4

Constituent (S2): 20% in 28 days (O₂ consumption, OECD 301F)

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Type of water:

freshwater

Additional information

There are no reliable ready biodegradation data available for the reaction mass of S2 (4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane) and S3 (4,4,14,14-tetraethoxy-3,15-dioxa-8,9,10-trithia-4,14-disilaheptadecane) as a whole substance, therefore good quality data for the structurally-related substance, reaction mass of S2, S3 and S4 (4,4,15,15-tetraethoxy-3,16-dioxa-8,9,10,11-tetrathia-4,15-disilaoctadecane) (CAS 211519-85-6) has been read-across.

The registered substance is a multi-constituent substance containing both S2 and S3. The S2 constituent of the registered substance (CAS 56706 -10 -6) has a measured ready biodegradation value of 20% in 28 days (O₂consumption) which was conducted according to OECD 301F and in compliance with GLP.

In contact with water, the constituents of the registered substance, reaction mass of S2 and S3, reacts slowly to form (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol and (3-{[3-(trihydroxysilyl)propyl]trisulfanyl}propyl)silanetriol and ethanol. Similarly, the read across substance, reaction mass of S2, S3 and S4 (CAS 211519-85-6), in contact with water, the constituents react moderately to slowly to form (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol, (3-{[3-(trihydroxysilyl)propyl]trisulfanyl}propyl)silanetriol, [3-({[3-(trihydroxysilyl)propyl]disulfanyl}disulfanyl)propyl]silanetriol and ethanol.

Ethanol is readily biodegradable (OECD 2004).

The registered substance, the read-across substance and S2 constituent of the registered substance are within a group of substances within which, in general, there is no evidence of any significant biodegradation once biodegradation of alkoxy/acetoxy groups has been taken into account.

This analogue group for the ready biodegradability endpoint consists substances with similar structure and/or functional group such as sulphide groups.

The table below presents ready biodegradation data for relevant substances. The three substances are members of this class.

It is therefore considered valid to read-across the results for reaction mass of S2, S3 and S4 and for S2 to fill the data gap for the registered substance. Additional information is given in a supporting report PFA (2013f) attached in Section 13.

 

Table: Ready biodegradation data for relevant substances

 

 

CAS	Name	Readily biodegradable? Yes/no	Result: Biodegradation after 28 days (%)	Guideline	Test type	Klimisch code	Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for[1]
056706-10-6	4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane	No	20%	OECD 301F	BOD	1	-47
211519-85-6	Reaction mass of 4,4,15,15-tetraethoxy-3,16-dioxa-8,9,10,11-tetrathia-4,15-disilaoctadecane and 4,4,14,14-tetraethoxy-3,15-dioxa-8,9,10-trithia-4,14-disilaheptadecane and 4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane	No	5%	OECD 301C	BOD	1

 

[1]The negative values in this column are where the biodegradation rate observed in the test is less than that expected assuming only alkoxy parts biodegrade. This could be due to low solubility of parent substance or low rates of hydrolysis. These values should in effect be considered as zero.

 

In the study with S2, S3, and S4 (CAS 211519-85-6) using OECD 301F test method, 5% biodegradation (O₂consumption) in 28 days was attained. The S2 constituent of the registered substance (CAS 56706 -10 -6) has a measured ready biodegradation value of 20% in 28 days (O₂consumption) which was conducted according to OECD 301F and in compliance with GLP.

The biodegradation seen in these tests is likely to be a result of the biodegradation of hydrolysis product, ethanol, which is readily biodegradable. The biodegradation found in the tests is lower than expected based on consideration of the chemical structure and based on the assumption that the substances hydrolyse to release ethanol. The poor solubility of the test substances may have resulted in the degradation rate being limited by dissolution into water.

No significant biodegradation is expected of the silanol hydrolysis products.

 

Reference 

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.