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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:
other: GLP Guideline study
Qualifier:
according to guideline
Guideline:
other: Commission directive 88/302/EEC
Principles of method if other than guideline:
Corresponds to the test method OECD guideline 209: activated sludge; respiration inhibition test
GLP compliance:
yes
Analytical monitoring:
no
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Laboratory culture: no
- Source: Aeration tank of sewage treatment plant treating predominantly domestic sewage
- Sampling site: Wupper area water authority, Germany
- Pretreatment: none
- Initial biomass concentration: 400 mg/L sludge
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
30 min
Test temperature:
20 ±2 °C
pH:
7.3 (before application)
Nominal and measured concentrations:
Nominal: 1000, 1800, 3200, 5600 and 10000 mg/L
A blank control and a test with the reference substance 3.5-Dichlorophenol were also performed
Details on test conditions:
TEST SYSTEM
- Test vessel: no information available
- Material, size, headspace, fill volume: 250 mL culture medium
- Aeration: permanent
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1
- Biomass loading rate: 400 mg/L sludge

EFFECT PARAMETERS MEASURED : Respiration inhibition
- Analytical parameter: oxygen measurement
- Sampling: oxygen concentration determined over a period of 4 to 9 minutes

Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Duration:
30 min
Dose descriptor:
EC10
Effect conc.:
580 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
30 min
Dose descriptor:
EC50
Effect conc.:
3 080 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
30 min
Dose descriptor:
other: EC25
Effect conc.:
1 280 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
30 min
Dose descriptor:
other: EC75
Effect conc.:
7 420 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 = 16.0 mg/L
Reported statistics and error estimates:
The EC values were calculated with a probit analysis

Table 1:                 Test results

Test concentration
(mg/L)

Respiratory rate test substance (mg/L)

Phys. chem. O2-consumption (mg/L)

Respiratory rate-phys.chem. O2-consumption (mg/L)

Inhibition (%)

1000

24.9

0.0*

24.9

21.0%

1800

19.7

0.0

19.7

37.5%

3200

18.8

0.0

18.8

40.3%

5600

9.0

0.0

9.0

71.4%

10000

5.3

0.0

5.3

83.2%

Control, mean

31.5

-

-

-

Control 1

33.0

-

-

-

Control 2

30.0

-

-

-

Executive summary:

A toxicity test to microorganisms, corresponding to OECD guideline 209 with GLP, is available for this substance. The study is based on nominal concentrations of the test substance and the calculated, 30 minute, EC50 for respiration inhibition is 3080 mg/L. The test item is therefore has little toxic effect on activated sludge microorganisms and is not expected to inhibit the degradation activity of activated sludge.

Description of key information

Diuron is not expected to inhibit the degredation activity of activated sludge 

Key value for chemical safety assessment

Additional information

A toxicity test to microorganisms, corresponding to OECD guideline 209 with GLP, is available for Diuron. The study is based on nominal concentrations of the test substance and calculated the 30 minute EC10 for respiration inhibition to be 580 mg/L, with an EC50 of 3080 mg/L. The test item is therefore has little toxic effect on activated sludge microorganisms and is not expected to inhibit the degradation activity of activated sludge (Caspers and Mueller, 1998).