SDBR

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

20 and 21 June 2000

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

Version / remarks:

1984

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Storage temperature: room temperature

Analytical monitoring:

no

Vehicle:

yes

Remarks:

Tertiary butyl alcohol (used for the three lowest concentrations only)

Details on test solutions:

Control mixtures of 16 mL synthetic sewage feed and 284 mL dilution water were prepared in one liter glass beakers. An additional control was added containing 0.1 mL vehicle.
A series of 16 mL synthetic sewage feed, 284 mL dilution water, appropriate amounts of the test substance or its stock solution brought to 284 mL with dilution water were prepared in 1 liter beakers. The final nominal test concentrations were 0, 3.2, 10, 32, 100, 321 and 1000 mg/L.
Tertiary butyl alcohol was used for the three lowest concentrations; for the three highest concentrations the test item was added directly to the test mixture.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Source sludge: oxidation ditch situated in the district of Hazerswoude Dorp, The Netherlands (domestic sewage treatment).
Sludge was centrifuged and washed twice in tap water and once in dilution water. The mixed liquor suspended solids content was found to be 7.1 g/L. The suspension was aerated vigorously and kept at approximately 20ºC. Fifty mL of synthetic sewage feed was added daily per liter of sludge suspension. The dry weight was checked prior to use in the test and a mixed liquor suspended solids level of 4.2 g/L was found.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20ºC

pH:

7.6

Details on test conditions:

The suspensions were aerated vigorously and incubated at approximately 20ºC for three hours. After three hours, a sample of each mixture was poured into a BOD (Biochemical Oxygen Demand) bottle (volume about 295 mL) and stirred vigorously on a magnetic stirrer. An oxygen electrode was inserted into the sample and the oxygen concentration was recorded every minute during a period of about 10 minutes.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol at 5, 12 and 30 mg/L

Duration:

3 h

Dose descriptor:

IC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Details on results:

The results are included below.
No dose response relation was found for the respiration inhibition within the nominal concentration range of 3.2 to 1000 mg/L. The respiration rate within this range was on average 0.2% below the average of the initial and final control.

Results with reference substance (positive control):

The EC50 of 3,5-dichlorophenol was found to be 5.02 mg/L (within the acceptable range of the OECD guideline).
The respiration rates of the initial and final controls were found to be 15.21 and 17.37 mg O2/g/h, respectively. The difference between the two values amounted to 13.3% being within the validity criterion (15%) of the OECD guideline.

Validity criteria fulfilled:

yes

Conclusions:

SDBR was found not to inhibit microbial activity (NOEC = 1000 mg/L, based on nominal values).

Description of key information

SDBR was found not to inhibit microbial activity (NOEC = 1000 mg/L, based on nominal values).