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

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2009-09-03 to 2009-09-03

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

- Sampling method: 46ul of the test substance which corresponds to 50 mg, was pipetted below the surface of the Milli-RO water and stirred briefly to mix (5 minutes). Synthetic sewage was subsequently fed and sludge added (final volume 500 ml) and the test was initiated. A loading rate of 100 mg/l was tested in duplicate.

- Sample storage conditions before analysis: Test substance stored at room temperature in the dark

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Pretreatment: The sludge was coarsely sieved to remove large particles. The sludge was then washed by centrifuging at 1000 g for 10 minutes. The supernatant was decanted and replaced with ISO-medium. The washing step was performed three times. A small amount of the sludge was weighed and dried overnight at ca. 105 C to determine the amount of suspended solids.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

20 ± 2°C

pH:

7.4

Dissolved oxygen:

46 ul of test substance, Milli-RO water, synthetic sewage feed (16 ml) and activated sludge (200 ml) were mixed and made up to 500 ml with Milli-RO water in a 1 L bottle. The mixture was aerated during the contact time, using a pipette as an aeration device.

Details on test conditions:

TEST SYSTEM
- Test vessel:All glass, approximately 300 ml oxygen bottles and 1 L test bottles

- Type (delete if not applicable): open

- Aeration: Strong aeration with clean, oil-free air

- Type of flow-through (e.g. peristaltic or proportional diluter): peristaltic

- No. of organisms per vessel: Number of micro-organisms was determined as the amount of mixed liquor suspended solids (MLSS) per litre of test medium.

- Biomass loading rate: 100 mg/l


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Tap-water was purified by reverse osmosis (Mill-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Mill-Q).

Reference substance (positive control):

yes

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Results with reference substance (positive control):

- Results with reference substance valid? Yes

Reported statistics and error estimates:

Regression line: Y = 43.61 X + 9.02 (See Appendix I) of attached report

Table 2: Study plan

Flask	Test Substance (µl)	Synthetic sewage feed (ml)	Stock sol. R 0.5 g/l (ml)	Activated sludge (ml)	Made up to 500 ml with Mill-RO water	Exposure time (h)	Conc/ loading rate (mg/l)
C start R	-	16	-	200	+	8.00 – 11.00	0
R1	-	16	5.0	200	+	8.15 – 11.15	5.0
R2	-	16	12	200	+	8.30 – 11.30	12
R3	-	16	30	200	+	8.45 – 11.45	30
C end R	-	16	--	200	+	9.00 – 12.00	0
C start T	-	16	-	200	+	9.45 – 12.45	0
T1	46 (=50 mg)	16	-	200	+	10.00 – 13.00	100
T2	46 (=50 mg)	16	-	200	+	10.15 – 13.15	100
C end T	-	16	-	200	+	10.30 – 13.30	0

C: Control

R: Reference substance, 3,5-dichlorophenol

T: Test substance, Bis[3-(triethoxysilyl)propyl]poluysulfides

Table 3: Controls (C) and Bis[3-(triethoxysilyl)propyl]poluysulfides (T): pH, oxygen concentration, oxygen consumption and percentage inhibition of the respiration rate

Flask	loading rate (mg/l)	Oxygen conc. At the start (~mg O2/l)	Oxygen consumption (mg O2/l/h)	% Respiration rate	pH
C start T	0	7.4	29	-	8.2
C end T	0	7.9	28	-	8.3
T1	100	5.3	29	-2^1	8.1
T2	100	7.1	30	-5^1	8.2

¹: Negative values indicate stimulation of the respiration rate sludge. The values are considered not significant

Validity criteria fulfilled:

yes

Conclusions:

An activated sludge respiratory inhibition test value EC50 exceeding a loading rate of 100 mg/L has been determined for Bis[3-(triethoxysilyl)propyl]poluysulfides in a test conducted according to OECD 209. The result is considered reliable.

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Please see IUCLID Section 6.1.7 endpoint summary for justification of read-across.

Reason / purpose for cross-reference:

read-across source

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Description of key information

ASRI 3-hour EC₅₀: >100 mg/l (loading rate) (OECD 209), read-across from a structurally-related substance. Organisms were likely predominantly exposure to parent test substance.

Additional information

There are no microorganism toxicity data available for 4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane (S2) (CAS 56706-10-6, EC 260-350-7), therefore good quality data for the structurally-related substance bis[3-(triethoxysilyl)propyl]polysulfides, (CAS 211519-85-6, EC 915-673-4), have been read across.

S2 is present as a constituent in bis[3-(triethoxysilyl)propyl]polysulfides, which is a multi-constituent substance. The registration substance, S2, contains a central disulfide group linking two 3-(triethoxysilyl)propyl groups. The other two constituents of CAS 211519-85-6 contain a central trisulfide or tetrasulfide group linking two 3-(triethoxysilyl)propyl groups. S2 and the other constituents of bis[3-(triethoxysilyl)propyl]polysulfides hydrolyse at a moderate or slow rate to structurally similar silanol products; the other hydrolysis product being ethanol. Ethanol is not expected to have adverse effects on microorganisms.

S2 and bis[3-(triethoxysilyl)propyl]polysulfides are within an analogue group of substances that exhibit no evidence of significant toxicity to microorganisms.

This analogue group for the toxicity to microorganisms endpoint consists of a number of sub-classes of substances (based on structure/functionality) with different main codes (used to represent the different sub-classes). However, read-across is carried out between substances with the same main code in most cases. The table below presents all microorganism toxicity data available for substances within the sulfidosilanes analogue group.

It is therefore considered valid to read-across the results for bis[3-(triethoxysilyl)propyl]polysulfides to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013j) attached in Section 13.

An activated sludge respiration inhibition 3-hour EC₅₀ value of >100 mg/l (loading rate) was determined for bis[3-(triethoxysilyl)propyl]polysulfides in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP. This indicates that the test substance was not toxic to waste water (activated sludge) bacteria at a loading rate of 100 mg/l. This data represents the only toxicity to aquatic microorganisms data available for the sulfidosilanes analogue group.

References:

PFA 2013j: Peter Fisk Associates, STP Microorganism toxicity Main Analogue Group report, PFA.300.003.006