Registration Dossier

Ecotoxicological information

Toxicity to microorganisms

Currently viewing:

Administrative data

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:
2009-09-04
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
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)

- Method: 52 µl of the test substance, corresponding to 50 mg, was pipetted below the surface of the purified tap water and stirred.
Test organisms (species):
activated sludge
Details on inoculum:
- Source: Municipal sewage treatment plant: ‘Waterschap de Maaskant', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage

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

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:
19.0-20.4°C
pH:
8.1-8.4
Nominal and measured concentrations:
100 mg/L
Performance of a limit concentration at 100 mg/l is acceptable, because 100 mg/l is far above the water solubility of Dodecamethylcyclohexasiloxane and thus exceeds the expected concentration in a Sewage Treatment Plant.
Details on test conditions:
TEST SYSTEM

- Test vessel:

- Material, size, headspace, fill volume: 1L test bottle

- Aeration: continuous vigorous aeration during contact time

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

- No. of vessels per control (replicates): One at the initial, one at the final test points.

- Biomass loading rate: activated sludge: 3.8 g/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) (Millipore Corp.).
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Details on results:
The two control had a difference in respiration rate of 15%, which is the limit for a valid study.
Results with reference substance (positive control):
A positive control test with 3,5-dichlorophenol yielded an EC50 of 7.2 mg/L. The validity criteria of the Guideline were fulfilled.

Test sample

Nominal concentration of test substance (mg/l)

Oxygen conc. At start (mg O2/l)

Oxygen consumption (mg O2/l/h)

% Inhibition

respiration rate

pH

 

 

Initial control

0

7.5

33

-

8.4

Final control

0

7.0

38

-

8.3

Dodecamethylcyclohexasiloxane (1)

100

5.4

38

-7

8.2

Dodecamethylcyclohexasiloxane (2)

100

4.2

39

-10

8.1

 

 

3,5-dichlorophenol

5

-

-

43

-

12

-

-

61

-

30

-

-

67

-

Validity criteria fulfilled:
yes
Conclusions:
An EC50 >100 mg/l for toxicity to microorganisms 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: EC50 > 100 mg/L (OECD 209)

Key value for chemical safety assessment

Additional information

A 3-hour EC50 >100 mg/l for toxicity to microorganisms was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.