Trimethoxypropylsilane

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 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

GLP compliance:

yes

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
- Name of test material (as cited in study report): Methyltrimethoxysilane

- Physical state: Clear colourless liquid

- Analytical purity: 96.4 ± 0.2%. (n=3)

- Purity test date: 7th May 2009

- Lot/batch No.: 0005552461

- Expiration date of the lot/batch: 01 March 2012

- Storage condition of test material: At room temperature in the dark

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
53 µl of the 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 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. The pH was 7.7 on the day of testing. The batch of sludge was used one day after collection; therefore 50 ml of synthetic sewage feed was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

- 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:

Oxygen consumption was measured and recorded for approximately 10 minutes.

Test temperature:

19.9-20.3°C

pH:

8.2 to 8.3

Nominal and measured concentrations:

100 mg/l (loading rate). Performance of a limit concentration at 100 mg/l is acceptable, because 100 mg/l exceeds the expected concentration in a Sewage Treatment Plant.

Details on test conditions:

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

- Aeration: continuous

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

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

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, tested in duplicate

- Justification for using less concentrations than requested by guideline: No significant inhibition of respiration rate of the sludge was recorded for the test substance at a loading rate of 100 mg/L in both replicates and therefore no further testing was required.

Reference substance (positive control):

yes

Remarks:

(3,5-Dichlorophenol)

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

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The two controls had a difference in respiration rate of 6%, 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	7.3	34	-	8.3
Final control	0	6.5	32	-	8.2
Trimethoxy(methyl)silane replicate (1)	100	7.1	33	0	8.3
Trimethoxy(methyl)silane replicate (2)	100	7.1	31	6	8.3
3,5-dichlorophenol	5	-	-	38	-
	12	-	-	59	-
	30	-	-	72	-

 

 

Validity criteria fulfilled:

yes

Conclusions:

An activated sludge respiration inhibition 3hr 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.

Description of key information

EC10 (3 h) > 100 mg/L (nominal, OECD 209, activated sludge); read-across CAS No. 1185-55-3

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

For the toxicity to microorganisms, no data are available for trimethox(propyl)silane (CAS No. 1067-25-0). Therefore, read-across was performed from the structurally similar analogue substance trimethoxy(methyl)silane (CAS No. 1185-55-3). Both substances hydrolyse to structurally-related silanol hydrolysis products, propylsilanetriol (registered substance) and methylsilanetriol (read-across substance), respectively.

 

For trimethoxy(methyl)silane (CAS No. 1185-55-3) one experimental study according to OECD 209 and GLP is available which was performed as a static limit test. No effects were observed at the limit concentration tested, indicating that the substance was not toxic to waste water activated sludge bacteria at a loading rate of 100 mg/L.