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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:
04/03/1991-05/03/1991
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
study has been conducted according to valid study guidelines. Deviations are in the number and values of concentrations . This is not expected to compromise the quality of the study results.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
yes
Remarks:
See method description
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
Method of preparation: direct dispersion in water
Test organisms (species):
other: a mixed population of activated sewage sludge microorganisms
Details on inoculum:
- Source: The aeration Stage of Severn Trent PLC Sewage Treatment Plant, Belper, Derbyshire.
Preparation: the sample was maintained at 21°C and used on the day of collection.
Test type:
not specified
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
21°C
pH:
The pH was buffered to pH 7.0 with sodium hydroxide solution
Dissolved oxygen:
continuous aeration
Nominal and measured concentrations:
Range Finding Study:
- Test: 10, 100 and 1000 mg/l
- Reference: 3.2 and 32 mg/l
Definitive Study:
- Test 1000 mg/l R1-R3 replicates
- Reference: 3.2 and 32 mg/l
Details on test conditions:
The suspended solids level was adjusted to 3.9 g/l prior to use
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
R1-R3: replicates R1-R3
Results with reference substance (positive control):
Reference material, 3,5-dichlorophenol: EC50 (3 hour contact time) = 12 mg/l
Reported statistics and error estimates:
Range Finding Study: Variation between controls: +/-4%
Definitive Study: Variation between controls: +/-1%

Range finding study

Date: 4th March 1991

 Concentration (mg/l)

 O2 consumption rates mg/O2/l/min

 

% Inhibition 

3 hour contact time

Control

R1

0.60

-

 

R2

0.55

Test

10

0.57

 1

 

100

 0.63

<10 >

 

1000

 0.60

  <4 >

Reference

3.2

 0.55

   4

 

32

 0.09

 84

<increase>

Variation between controls: ± 4%

Definitive study

Date: 5th March 1991

 Concentration (mg/l)

 O2 consumption rates mg/O2/l/min

 

% Inhibition 

3 hour contact time

Control

R1

0.57

-

 

R2

0.56

Test

1000  R1

0.54

 4

 

1000  R2

 0.50

 12

 

1000  R3

 0.50

  12

Reference

3.2

 0.56

   1

 

32

 0.08

 86

R1 -R3: replicates R1 -R3

Variation between controls: ± 1%

Validity criteria fulfilled:
yes
Conclusions:
The test substance is non-toxic to microorganisms.
Executive summary:

A study was performed to assess the effect of the test substance phenol 2,6 bis-(1,1-dimethylethyl) on a mixed population of activated sewage sludge microorganisms. The method used followed that described in the OECD Guidelines for testing of Chemicals / Section 2: Effects on Biotic Systems, Test No. 209 "Activated Sludge, Respiration Inhibition Test". Deviations are in the number and values of concentrations (this is not expected to compromise the quality of the study results). 3,5 -dichlorophenol was the reference substance at 3.2 and 32 mg/l. O2 consumption rates were measured after 3 h contact time at concentrations of 10, 100 and 1000 mg/l of test substance in the range finding study, and 1000 mg/l for the 3 replicates in the definitive study. Variation between controls was ± 4% in the range finding study and ± 1% in the definitive study. EC50 value (3h contact time) for reference substance was 12 mg/l. EC50 value (3h contact time) for test substance was >1000 mg/l.

Description of key information

EC50 (3h contact time) >1000 mg/L (OECD 209)

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L

Additional information

Phenol 2,6 bis-(1,1dimethylethyl) was evaluated for its toxicity on a mixed population of activated sewage sludge microorganisms. EC50 value (3h contact time) for test substance was >1000 mg/l. The test substance is therefore considered to be non-toxic to microorganisms.

Test method:

The method used followed that described in the OECD Guidelines for testing of Chemicals / Section 2: Effects on Biotic Systems, Test No. 209 "Activated Sludge, Respiration Inhibition Test". Deviations are in the number and values of concentrations (this is not expected to compromise the quality of the study results). 3,5 -dichlorophenol was the reference substance at 3.2 and 32 mg/l. O2 consumption rates were measured after 3 h contact time at concentrations of 10, 100 and 1000 mg/l of test substance in the range finding study, and 1000 mg/l for the 3 replicates in the definitive study. Variation between controls was ± 4% in the range finding study and ± 1% in the definitive study. EC50 value (3h contact time) for reference substance was 12 mg/l.