4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

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) R2 Test 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.

Description of key information

Biodegradation in water: screening tests: 20% biodegradation in 28 days (OECD 301F)

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater

Additional information

The substance attained 20% degradation in 28 days in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

 

4,4,13,13-Tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane (S2) hydrolyses within the timescale of the ready biodegradation study to (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol and ethanol. The biodegradation observed in the study is attributable to the biodegradation of the ethanol hydrolysis product.

 

Ethanol is readily biodegradable (OECD, 2004) and no significant biodegradation is expected for the silanol hydrolysis product.

 

The biodegradation rate is slightly lower than expected based on consideration of the chemical structure (biodegradable ethanol/ethoxy groups accounting for nearly 60% of the parent structure by weight). The toxicity control showed a slight bacterial inhibition (9.3%), which may explain the lower rate. Also, the study stated that the exact determination of the remaining COD of the test solution at the end of the test was not possible due the lack of homogeneity of the test substance in the aqueous solution. Therefore, the biodegradation due to ethanol is unlikely.

 

A second reliable study is available which gave a similar result to the key study, 10 -12% degradation in 28 days was achieved.

 

References:

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