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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
not specified
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Method of cultivation: Activated sludge from the municipal wastewater treatment plant of Mannheim, Germany was collected on 23 Feb 2010 from the aeration tank of the plant
- Preparation of inoculum for exposure: The sludge suspension was sieved with a fine woven mesh (mesh size about 1mm).
- Pretreatment: The suspension was pre-aerated over night at room temperature. At thenext day the sludge suspension was washed with tap water once. After that the suspension was adjusted to 7.5 g/L dry matter
- Initial biomass concentration: 1.5 g/L dry matter
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
180 min
pH:
7.2 at test start
7.9 - 8.0 at the end of the exposure
Nominal and measured concentrations:
nominal: blank, 62.4, 125, 250, 500 and 1000 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 ml Erlenmeyer-vessels
- Material, size, headspace, fill volume: glass, fill volume = 250 mL
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1
- Biomass loading rate: 1.5 g/L dry matter

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: 8 mL/vessel 100-fold concentrated OECD medium

OTHER TEST CONDITIONS
- Adjustment of pH: no

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : oxygen consumption

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2
Reference substance (positive control):
yes
Remarks:
3,5 dichlorophenol
Duration:
180 min
Dose descriptor:
EC10
Effect conc.:
450 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
180 min
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
180 min
Dose descriptor:
other: EC20
Effect conc.:
600 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? yes
- Relevant effect levels: EC50 = 8.0 mg/L
Reported statistics and error estimates:
The values were given with an accuracy of 2 significant digits. The degree of inhibition was evaluated by Probit analysis according to Finney

Assay identification

BC1

BC2

RS1

RS2

RS3

TS1

TS2

TS3

TS4

TS5

O2 concentration Start [mg/L]

7.4

7.0

7.4

8.5

8.8

8.3

7.7

7.6

7.7

7.1

O2 concentration after 6 minutes [mg/L]

6.0

5.5

6.0

8.0

8.7

7.5

6.5

6.0

6.0

5.0

O2 consumption rate [mg/L in 6 min]

1.4

1.5

1.4

0.5

0.1

0.8

1.2

1.6

1.7

2.1

O2 consumption rate [mg/L*h]

14

15

14

5

1

8

12

16

17

21

Specific O2 consumption rate [mg O2/g*h]

9

10

9

3

1

5

8

11

11

14

RS/TS concentrations [mg/L]

-

1

10

100

1000

500

250

125

62.4

Calculation of inhibition respiration [%]

-

-

3

66

93

45

17

-10

-17

-45

Legend: TS = test item, RS = reference item, BC = blank control

 

Validity criteria fulfilled:
yes
Conclusions:
The inhibition of the degradation activity of activated sludge is not anticipated when introduced to biological treatment plants in appropriate low concentrations.
Executive summary:

In this guideline (OECD 209) study with GLP certification, the 3 hour EC50 of the test material to sewerage microorganisms was determined to be >1000 mg/l (nominal). The test was conducted upon a washed activated sewerage sludge taken from a municipal sewerage treatment plant. The test material is not expected to inhibit sewerage microorganisms at low concentrations.

Description of key information

Study conducted to recognised training guidelines with GLP certification. 

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L

Additional information

In the key study on the toxicity of the test substance on activated sludge an EC10 of 450 mg/L and an EC50 of > 1000 mg/L was reported. The test was conducted under GLP regulations and according to OECD test guideline 209. The respiration inhibition was determined in activated sludge obtained from a municipal sewage treatment plant. The effect concentrations were derived after a test duration of 3 hours.

A supporting study was conducted using the test material before the final distillation and industrial activated sludge. The EC50 after 30 min was determined to be 3 mg/L. However, the value will not be used in the risk assessment since test material without the final distillation was used and a more reliable up-to-date key study is available.