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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1993
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
Deviations:
yes
Remarks:
deionised water instead of distilled water for the stock solution, - Preparation of the inoculum : higher sludge weight after the washing procedure (Sludge concentrations in the test according to the guidelines), - 4 instead of 5 test concentrations.
Qualifier:
equivalent or similar to guideline
Guideline:
other: EG Method Nr. L 133/118 "Belebtschlamm: Prüfung der Atmungshemmung" (Ausgabe: 30.05.1988)
GLP compliance:
yes
Specific details on test material used for the study:
Code number: 92368/A
EN/Batch: PLN 13
Purity: ca 80 %
Appearance: solid
Solubility: miscible
Storage: room temperature
Expiration date: 03/98
Analytical monitoring:
not specified
Details on sampling:
no data
Vehicle:
no
Details on test solutions:
no data
Test organisms (species):
activated sludge
Details on inoculum:
- Source: Activated sludge of a communal sewage treatment plant (ARA-Birsig Therwil).
- Pretreatment: 3 times washing with tap water and addition of synthetic sewage (1 d before the main test).
- Initial biomass concentration: 1560 mg/L.
Test type:
not specified
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Post exposure observation period:
no data
Hardness:
no data
Test temperature:
20.5 °C
pH:
7.2 before the test beginning
Dissolved oxygen:
no data
Salinity:
no data
Nominal and measured concentrations:
no data
Details on test conditions:
- Test concentrations: 320, 100, 32 and 10 mg/L
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol (three reference substance concentrations 32, 10 and 3.2 mg/L)
Key result
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
> 320 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Results with reference substance (positive control):
- Results with reference substance valid?: Valid.
- Relevant effect levels: The IC50 (3 h) of the reference substance 3,5-Dichlorophenol: 8.8 mg/L.
Reported statistics and error estimates:
no data

Table 1 presenting inhibition results for test substance

Test substance

(mg/L)

pH after 3h

O2-consumption

(in cm)

time

(in cm)

mg O2

pro min/L

%

of control

%

inhibition

320

7.5

2.2

4.7

0.37

53.62

46.38

100

7.7

2.9

4.5

0.52

75.36

24.64

32

7.7

2.8

3.5

0.64

92.75

7.25

10

7.7

3.5

4.2

0.67

97.10

2.90

Table 2 presenting inhibition results for positive control

3,5 -Dichlorophenol

(mg/L)

pH after 3h

O2-consumption

(in cm)

time

(in cm)

mg O2

pro min/L

%

of control

%

inhibition

32

7.9

0.7

4.5

0.12

17.39

82.61

10

7.8

1.9

4.8

0.32

46.38

53.62

3.2

7.8

3.2

4.7

0.54

78.26

7.25

Validity criteria fulfilled:
yes
Conclusions:
The IC50 of the test substance was determined to be >320 mg/L.
Executive summary:

A study was conducted to assess the inhibitory effect of the test substance (of ca. 80 % purity) on the oxygen consumption rate of aerobic microorganisms (activated sludge) according to OECD Guideline 209 in compliance with GLP.

A mixture of activated sludge from the domestic sewage and a range of concentrations of the test substance or the reference substance were incubated for a period of 3 h with continuous aeration. Test substance and reference substance 3,5-dichlorophenol were tested at nominal concentrations of 320, 100, 32 and 10 mg/L and 32, 10 and 3.2 mg/L, respectively. The respiration rate of each test concentration was calculated as a percentage of the mean of the two control respiration rates. The results were plotted on a logarithmic (concentration against % inhibition) graph, where the IC50 was evaluated. The reference substance yielded an IC50 value of 8.8 mg/L, which is within the prescribed range by guideline. Hence the validity criteria of the guideline were fulfilled. 46.38, 24.64, 7.25 and 2.90 % inhibitions were seen with 320, 100, 32 and 10 mg/L test concentrations respectively. Based on these findings, the IC50 of the test substance was determined to be >320 mg/L.

Description of key information

The IC50 to the bacterial population was determined to be 300 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
300 mg/L

Additional information

In the study (1993) conducted to assess the inhibitory effect of the test substance (of ca. 80 % purity) on the oxygen consumption rate of aerobic microorganisms (activated sludge) according to OECD Guideline 209 in compliance with GLP, the IC50 of the test substance was determined to be >320.0 mg/L.

In another study conducted with methodology similar to OECD 209, the IC50 of FAT 20049/E was found to be 300 mg/L.

Outcomes of the other supporting studies are presented below:

FAT 20049/D - 21d IC50 : 200 mg/L, 3h IC50 : > 100 mg/L

FAT 20049/A - 21 IC50 : > 300 mg/L