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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2019
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 (Carbon and Ammonium Oxidation))
GLP compliance:
yes
Analytical monitoring:
yes
Vehicle:
no
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Municipal sewage treatment plant of 31137 Hildesheim, Germany
Test type:
static
Water media type:
other: synthetic waste water
Remarks:
according to OECD 209
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
nominal 18 - 22 °C, actually measured 19.6 °C
pH:
The pH value of the activated sludge was determined prior to test start. The pH value of the synthetic waste water was determined prior to use and adjustment to 7.5 +/- 0.5 was not necessary.
Dissolved oxygen:
After 3 h incubation, the oxygen concentration of each control, reference item and test item replicate was determined by means of oximeter every 5 seconds after transferring the solution to the measuring chamber and the oxygen depletion was recorded for at least 5 minutes with the software PreSens Measurement Studio 2.
Details on test conditions:
Preparation of the Test Vessels:
Based on the results of the preliminary test it was concluded that the heterotrophic respiration as well as the nitrification are not inhibited. Therefore, the definitive study was carried out with the concentration of 1000 mg a.i./L in 3 replicates (limit test to determine the NOEC). The concentration was weighed out directly in Erlenmeyer flasks and stirred overnight.
Triplicates of the control without test item were included at the beginning and at the end of the test.
The reference item was tested with three concentrations within the concentration range 58 - 180 mg/L and a dilution factor of approx. 1.8.
A fresh sample of activated sludge taken from the sewage plant Hildesheim was used for the test procedure. It was washed twice and adjusted with chlorine free tap water to a dry sludge concentration of 3.0 g/L +/- 10 %.
The oxygen uptake rates of all samples were determined following an incubation period of 3 h.
Reference substance (positive control):
yes
Remarks:
Copper (II) sulphate pentahydrate p.a.
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks on result:
other:
Remarks:
based on test item concentration

From the oxygen depletion the oxygen uptake rates were calculated in mg O2/L * h, additionally the specific respiration rates based on the dry sludge concentration were calculated in mg O2/g * h. The inhibition of the oxygen uptake rates of the test item concentrations in % was calculated in comparison to the oxygen uptake rates of the control. The results are listed in Table 3 to Table 4.

Table 3: Oxygen Uptake Rates of the Control Replicates

   Repl.  Oxygen Concentration* [mg/O2/L]  Oxygen Uptake Rate R [mg O2/(L x h)]  Specific Respiration Rate Rs [mg O2/gxh]
 

1

2

3

4

5

6

7.18

7.24

7.44

7.19

7.52

7.17 

27.0

29.3

29.3

32.7

34.0

33.9 

18.6

20.2

20.2

22.6

23.4

23.4 

   Mean value   31.0  21.4
   Standard deviation  2.65  
   CV [%]  8.55  

*) determined at start of the measurement

Repl. = Replicate

CV = Coefficient of variation

Table 4: Oxygen Uptake Rates and Inhibition of the Respiration of the Test Item Concentration

 Test item Concentration [mg a.i./L] Repl.   Oxygen Concentration* [mg O2/L]  Oxygen Uptake Rate R [mg O2/(Lxh)]  Inhibition [%]  Mean Inhibition [%]
 1000

1

2

3

5.59

6.19

5.19 

30.8

30.7

30.5

1

1

 1

*) determined at start of the measurement

Repl. = Replicate

In the reference test the EC50 value for copper (II) sulphate pentahydrate was determined with EC50 = 105 mg/L, 95 % Confidence Interval = 99.1 - 111 mg/L. This is the recommended range of validity of 53 - 155 mg/L.

Validity criteria fulfilled:
yes
Conclusions:
The NOEC of the test item is >= 1000 mg a.i./L.
Executive summary:

A study was performed according to OECD 209 guideline and GLP principles. In the study, the test item caused no inhibiting effects on activated sludge of a municipal sewage treatment plant at the limit test item concentration of 1000 mg a.i./L.

Description of key information

A study was performed according to OECD 209 guideline and GLP principles. In the study, the test item caused no inhibiting effects on activated sludge of a municipal sewage treatment plant at the limit test item concentration of 1000 mg a.i./L.

Key value for chemical safety assessment

Additional information