Tris(2-methoxyethoxy)vinylsilane

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

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

Version / remarks:

April 4, 1984

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Version / remarks:

2007

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

The test substance was pipetted below the surface of the Milli-RO-water (tap water purified by reverse osmosis; Millipore Corp. Bedford, Mass., USA) and stirred briefly to mix (5 minutes).

Subsequently, synthetic sewage feed and sludge was added and the test was initiated applying a 3 hour contact time. A loading rate of 100 mg/L was tested in duplicate.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Known volume 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 litre bottle.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Preparation of inoculum for exposure: The sludge was coarsely sieved then washed.

- Initial biomass concentration: 3.8 g/l

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

The oxygen consumption was measured and recorded for approximately 10 minutes. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer.

Test temperature:

18-20°C

pH:

8.0-8.1

Nominal and measured concentrations:

100 mg/l (nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel:

- Material, size, headspace, fill volume: glass, 300ml oxygen bottles and 1L test bottles

- Aeration: continuous

- No. of vessels per concentration (replicates): two

- No. of vessels per control (replicates): two

- Biomass loading rate: 100 mg/L


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: tap water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q)

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :

After the 3-hour contact time, a well mixed sample of the contents of the reaction mixture was poured into a 300 ml oxygen bottle, and the flask was sealed with an oxygen electrode connected to a recorder, forcing the air out of the vessel. WTW inolab Oxi 730 supplied with a WTW CellOx 325 oxygen electrode, electrolyte type ELY/G

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 100 mg/L only

- Justification for using less concentrations than requested by guideline: No significant inhibition of respiration rate of the sludge was recorded at 100mg Trichloro(vinyl)silane per litre. Therefore no further testing was required.

Reference substance (positive control):

yes

Remarks:

3,5 - Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

The two controls had a difference in respiration rate of 7%, which is less than the 15% limit required by the guideline for a valid study.

Results with reference substance (positive control):

A positive control test with 3, 5-Dichlorophenol yielded an EC50 of 8.7 mg/L, which is within the accepted range of 5 to 30 mg/l required by the guideline for a valid study.

Table 1: Results of the activated sludge respiration inhibition test

Test sample	Loading rate (mg/l)	Oxygen conc. at start (mg O2/l)	Oxygen consumption (mg O2/l/h)	% Inhibition respiration rate	pH
Initial control	0	7.9	28	-	8.3
Final control	0	6.8	30	-	8.2
Trichloro(vinyl)silane replicate (1)	100	=5.7	27	7	8.1
Trichloro(vinyl)silane replicate (2)	100	7.2	30	-3	8.0
3,5-dichlorophenol	5	-	-	38	-
	12	-	-	59	-
	30	-	-	72	-

Validity criteria fulfilled:

yes

Conclusions:

An activated sludge respiration inhibition 3 hour EC50 value of >100 mg/L (loading rate) was determined 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. Due to the rapid hydrolysis of the substance, it is likely the organisms were exposed to the hydrolysis products of the test substance, vinylsilanetriol and hydrochloric acid. The EC50 expressed as the silanol hydrolysis product is >72 mg/L.

Description of key information

Toxicity to microorganisms: ASRI 3 hour EC₅₀ >100 mg/L (loading rate) (OECD 209), read-across from an analogous substance.

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L

Additional information

An activated sludge respiration inhibition 5-hour EC₁₀ value of 2.0 ml/L (equivalent to 2.04 g/L based on a density of 1.02 g/cm³, Pseudomonas putida) based on oxygen consumption/respiration inhibition was determined for the substance using a relevant test method and in compliance with GLP (Evonik 1993). The result is considered to be reliable but is not used as key study because (i) the study is a 5-hour study instead of the recommended 16-hour growth inhibition type test recommended in ISO 10712 Test Method (ii) the study used an emulsifier - nonylphenol ethoxylate to improve solubility of the test substance and (iii) no reference substance was used during the study.

Therefore, good quality data for the structurally-related substance trichloro(vinyl)silane (CAS 75-94-5) have been read across. Both substances hydrolyse rapidly to vinylsilanetriol; the other hydrolysis products being 2-methoxyethanol and hydrochloric acid respectively. In view of the rapid hydrolysis of the target and source substances (61.5 minutes and 5 seconds respectively at pH 7), it is the hydrolysis products that are relevant for environmental risk assessment.

Hydrochloric acid is not expected to have adverse effects on microorganisms in test systems where the pH is maintained within a favourable range.

2-Methoxyethanol, CAS 109-86-4, is well characterised in the public domain literature (including the registration data set and peer-reviewed data published in the HSDB database) and considered not hazardous to sewage microorganisms at the concentrations relevant to the study exposures in this data set and not contributory to any effects observed in the studies. In addition, 2 -methoxyethanol is readily biodegradable and as a result, the requirement to conduct a toxicity to microorganisms study would not be considered relevant for this non-silanol hydrolysis product.

Tris(2-methoxyethoxy)vinylsilane and trichloro(vinyl)silane are within an analogue group of substances that exhibit no evidence of significant toxicity to microorganisms.

This group consists of substances containing a number of different functional groups but specific read-across is between substances with similar functionality. Tris(2-methoxyethoxy)vinylsilane and trichloro(vinyl)silane are members of this group.

The table below presents microorganism toxicity data for substances relevant to tris(2-methoxyethoxy)vinylsilane (CAS 1067-53-4).

It is considered valid to read-across the results for trichloro(vinyl)silane (CAS 75-94-5) to fill the data gap for the registered substance since the source and target substances rapidly generate the same silanol hydrolysis product. Additional information is given in a supporting report (PFA 2013j) attached in Section 13.

Table: Microorganism toxicity data for relevant substances

CAS	Name	Result: E(I)C50 (mg/L)	Result: NOEC (or EC10/ EC20) (mg/L)	Guideline	Test method	Species	Duration (hour)	Reliability
1066-40-6	Hydroxytrimethylsilane	6670		OECD 209 and ISO 1892	ASRI		uncertain	2
31795-24-1	Potassium methylsilanetriolate		EC10 >100	OECD 209	ASRI		3	1
124-70-9	Dichloro(methyl)(vinyl)silane	>100	EC10 >100	OECD 209	ASRI		3	1
75-94-5	Trichloro(vinyl)silane		>100	OECD 209	ASRI		3	1
1185-55-3	Trimethoxy(methyl)silane	>100	EC10 >100	OECD 209	ASRI		3	1
2943-75-1	Triethoxyoctylsilane	>1000	=1000 Nitrification control indicated no heterotrophic inhibition of respiration rate	OECD 209	ASRI		3	1
16068-37-4	4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane	>8000	8000	DIN 38 412, Part 8 (Pseudomonas cell multiplication inhibition test)	growth inhibition test	P. putida	16	1
35435-21-3	Triethoxy(2,4,4-trimethylpentyl)silane	>100		OECD 209	ASRI		3	1
18395-30-7	Trimethoxy(2-methylpropyl)silane		EC10 1.3 ml/L	Huls AG method	oxygen consumption	P. putida	5.8	2 -don't use to derive PNEC*
2768-02-7	Trimethoxyvinylsilane		EC10 1.1 ml/L	Huls AG method	oxygen consumption	P. putida	5	2 -don't use to derive PNEC*

 * Emulsifier nonylphenol ethoxylate propoxylate used. Results should be used with caution. Also, reference substance not used

In the study with trichloro(vinyl)silane (CAS 75-94-5), an activated sludge respiration inhibition 3 h EC₅₀ value of >100 mg/L (loading rate) was determined in a reliable study conducted according to an appropriate test protocol and in compliance with GLP. The result indicate that the test substance was not toxic to wastewater (activated sludge) bacteria at a loading rate exceeding a value of 100 mg/L.

Reference:

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