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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From April 18, 2006 to April 21, 2006
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
Deviations:
no
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Type: mixed population of aquatic microorganisms (activated sludge)
- Origin: aeration tank of a domestic sewage treatment plant (Municipal STP Cologne-Stammheim)
- Pretreatment: aeration of the activated sludge, daily fed with synthetic medium
- pH of the suspension before application: 7.8
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
21.3-21.9°C
pH:
Control = 8.1
Test = 7.7-7.9
Reference substance: 8.1
Dissolved oxygen:
Control:
Start = 5.0-5.3 mg/L; End = 2.8-3.3 mg/L

Reference substance:
Start = 4.0-6.1 mg/L; End = 2.8-5.4 mg/L

Test:
Start = 3.9-4.3 mg/L; End = 2.7-2.9 mg/L
Nominal and measured concentrations:
- Type of test material application: direct weighing (The test item was added to about 130 mL of deionized water and stirred overnight before testing)
- Test concentrations (nominal): 100, 1000 and 10,000 mg/L
- Test substance concentration in physico-chemical oxygen consumption control (nominal): 10,000 mg/L
- Concentration of reference substance '3,5-dichlorophenol' (nominal): 5, 10 and 20 mg/L
Details on test conditions:
- Test concentration of the activated sludge: 1,200 mg/L suspended solids
- Incubation: 3 h with permanent aeration
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol (97% purity; Batch number: 15809K1-392)
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 10 000 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:
NOEC
Effect conc.:
>= 10 000 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):
- EC50 for reference substance = 11.0 mg/L
Reported statistics and error estimates:
The EC50 value was determined by probit analysis.

Table 1: Inhibition of respiration

Treatment group

Concentration

[mg/L]

Respiratory rate

mg/[L×h]

% inhibition of respiration

Control

-

31.5

-

Test substance

100

31.3*

0.6

Test substance

1,000

32.3*

0

Test substance

10,000

35.3*

0

Reference substance (3, 5 dichlorophenol)

5

24.0 23.8

Reference substance (3, 5 dichlorophenol)

10

18.0 42.9

Reference substance (3, 5 dichlorophenol)

20

8.4 73.3

* Respiratory rate adjusted for physico-chemical oxygen consumption of 0.7 mg/[L×h] at a test substance concentration of 10,000 mg/L.

Validity criteria fulfilled:
yes
Conclusions:
Under the test conditions, the NOEC of the test substance was >=10,000 mg/L, indicating a low toxicity to microorganisms.
Executive summary:

A study was conducted to assess the toxicity of the test substance to sludge microorganisms, according to EU Method C.11 (similar to OECD Guideline 209), in compliance with GLP.

Activated sludge from domestic sewage was exposed to nominal test substance concentrations of 100, 1000 and 10,000 mg/L. The respiration rates of each of these mixture was determined after an aeration period of 3 h and compared to data from the control and the reference substance 3,5-dichlorophenol.

The reference substance produced 23.8, 42.9 and 73.3% inhibition of respiration at 5, 10 and 20 mg/L respectively. The test substance produced 0.6, 0 and 0% inhibition of respiration at concentrations of 100, 1000 and 10,000 mg/L respectively.

Under the test conditions, the EC50 of the test substance was >10,000 mg/L, indicating a low toxicity to microorganisms.

Description of key information

The NOEC of the test substance was >=10,000 mg/L, indicating a low toxicity to microorganisms.

Key value for chemical safety assessment

EC50 for microorganisms:
10 000 mg/L
EC10 or NOEC for microorganisms:
10 000 mg/L

Additional information

A study was conducted to assess the toxicity of the test substance to sludge microorganisms, according to EU Method C.11 (similar to OECD Guideline 209), in compliance with GLP. Activated sludge from domestic sewage was exposed to nominal test substance concentrations of 100, 1000 and 10,000 mg/L. The respiration rates of each of these mixture was determined after an aeration period of 3 h and compared to data from the control and the reference substance 3,5-dichlorophenol. The reference substance produced 23.8, 42.9 and 73.3% inhibition of respiration at 5, 10 and 20 mg/L respectively. The test substance produced 0.6, 0 and 0% inhibition of respiration at concentrations of 100, 1000 and 10,000 mg/L respectively. Under the test conditions, the EC50 of the test substance was >10,000 mg/L, indicating a low toxicity to microorganisms (Weyers, 2006e).