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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
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
57 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:
18.4-19.4°C
pH:
8.2
Details on test conditions:
TEST SYSTEM

- Test vessel:

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

- Aeration: continuous during 3 hour test period

- 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: 100mg/L only

- 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
Details on results:
The two controls had a difference in respiration rate of 0%, 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

7.6

29

-

8.2

Final control

0

7.4

29

-

8.2

Triethoxy(2,4,4-trimethylpentyl)silane replicate (1)

100

7.5

29

0

8.2

Triethoxy(2,4,4-trimethylpentyl)silane replicate (2)

100

7.8

29

0

8.2

 

 

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.

Description of key information

Toxicity to microorganisms: ASRI 3-hour EC50 >100 mg/L (OECD 209).

Key value for chemical safety assessment

EC50 for microorganisms:
100 mg/L

Additional information

An activated sludge respiration inhibition 3-hour EC50 (total respiration) value of >100 mg/L was determined for the substance in a reliable study conducted according to an appropriate test protocol and in compliance with GLP. The result is considered to be reliable.

Under the conditions of this present test, triethoxy(2,4,4-trimethylpentyl)silane was not toxic to wastewater (activated sludge) bacteria up to and including a loading rate of 100 mg/L.

The EC50 exceeded a loading rate of 100 mg/L.