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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:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes
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)
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
Remarks:
respiration rate
Key result
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.
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 refer to overall summary (IUCLID Section 6.1.7) and attached justification for grouping in IUCLID Section 13.
Reason / purpose:
read-across source
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
Remarks:
respiration rate
Key result
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
Validity criteria fulfilled:
yes
Conclusions:
An activated sludge respiration inhibition 3 hour EC50 value of >100 mg/l (loading rate) was determined for the read across substance in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP. Therefore the target substance is considered not to be toxic activated sludge bacteria at loading rates up to 100 mg/l.

Description of key information

3 hour EC50 >100 mg/l; based on RA to trimethoxy(methyl)silane 

Key value for chemical safety assessment

Additional information

No data are available on the toxicity of triethoxy(methyl)silane to microorganisms. Therefore, good quality data for the analogue substance, trimethoxy(methyl)silane, have been read across. Both substances share the same silanol hydrolysis product, methylsilanetriol. Both triethoxy(methyl)silane and trimethoxy(methyl)silane are within an analogue group of substances that exhibit no evidence of significant toxicity to microorganisms. It is therefore considered valid to read-across the results from trimethoxy(methyl)silanet o fill the data gap for the registered substance.

Table 7.4.2 presents microorganism toxicity data available for substances within the sub-class of alkoxysilanes, silanols, acetoxysilanes and chlorosilanes, etc, where the Si part is of low-biological reactivity, once hydrolysis has been taken into account. Both trimethoxyoctylsilane and triethoxyoctylsilane are members of this sub-class.

Table 7.4.2 Microorganism toxicity data available for substances within the relevant sub-class of chemicals.

CAS

Name

Result: E(I)C50 (mg/l)

Result: NOEC (or EC10/ EC20) (mg/l)

Guideline Number

Test method

Species

Duration

Reliability

001000-50-6

Butylchlorodimethylsilane

>340

 

88/302/EC

ASRI

 

3h

1a

001066-40-6

Hydroxytrimethylsilane

6670

 

OECD 209 and ISO 1892

ASRI

 

Uncertain

1a

001185-55-3

Trimethoxy(methyl)silane

>100

 

OECD 209

ASRI

 

3hr

1a

031795-24-1

Potassium methylsilanetriolate

>100

 

OECD 209

ASRI

 

3 h

1a

087135-01-1

1,6-Bis(trimethoxysilyl)hexane

>1000

 

OECD 209

ASRI

 

3h

1a

017980-47-1

Triethoxyisobutylsilane

>1000

≥1000

OECD 209

ASRI

 

3h

1a

005894-60-0

Trichloro(hexadecyl)silane

>1000

 

OECD 209

ASRI

 

3h

1a

016415-12-6

Hexadecyltrimethoxysilane

>1000

 

OECD 209

ASRI

 

3 hr

1a

002943-75-1

Triethoxyoctylsilane

>1000

 

OECD 209

ASRI

 

3 hr

1a

016068-37-4

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 h

1c

035435-21-3

Triethoxy(2,4,4-trimethylpentyl)silane

>100

 

OECD 209

ASRI

 

3hr

1a

018395-30-7

Trimethoxy(2-methylpropyl)silane

 

EC10 1.3 ml/l

Huls AG method

oxygen consumption

P putida

5.8 h

2c -don't use to derive PNEC

142877-45-0

Silane, trimethoxy(1,1,2-trimethylpropyl)-

>1000

1000

OECD 209

ASRI

 

3 hr

1a

013154-25-1

Chlorotri(3-methyl-propyl)silane

>1000

100

OECD 209

ASRI

 

3 hr

2b

126990-35-0

Dicyclopentyldimethoxysilane

>water solubility

 

OECD 209//EU C11/Huls AG method (WOE)

ASRI/ASRI/oxygen consumption P putida

 

3 hr

1a/1a/2c

139147-73-2

Silane, dichlorodicyclopentyl-

>100

 

OECD 209

ASRI

 

3 hr

1a

 

Additional information is given in a supporting report (PFA, 2013) attached in Section 13 of the IUCLID dossier.

An activated sludge respiration inhibition 3 hour EC10value of >100 mg/l (loading rate) was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP (2009). On this basis it is assumed that trimethoxy(methyl)silane is not toxic to activated sludge bacteria at loading rates up to 100 mg/l.