Dichlobenil

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:

18 February 2002 to 21 February 2002

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Method of cultivation: maintained in the laboratory on continuous aeration at 21 °C

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Hardness:

100 mg/L as CaCO3

Test temperature:

21 °C

pH:

8.2-8.3

Nominal and measured concentrations:

1000 mg/L (nominal)

Details on test conditions:

EXPERIMENTAL PREPARATION
500 mg test material was dispersed in approximately 250 mL water and subjected to ultrasonication for approximately 30 minutes. 16 mL synthetic sewage, 200 mL activated sewage sludge and water were added to a final volume of 500 mL to give the required concentration of 1000 mg/L. This was performed in triplicate.

Additionally, a single test concentration was prepared by adding 10.5 mg of test material to approximately 250 mL water and subjecting to ultrasonication for approximately 30 minutes. 16 mL synthetic sewage, 200 mL activated sewage sludge and water were added to a final volume of 500 mL to give a test concentration of 21 mg/L.

PREPARATION OF TEST SYSTEM
At time 0, 16 mL of synthetic sewage was diluted to 300 mL with water and 200 mL of inoculum in a conical flask (first control). The mixture was aerated. At 15 minute intervals, the procedure was repeated with appropriate amounts of reference material being added. The test material vessels were prepared as described above followed by a second control.

As each vessel reached 30 minutes contact time, an aliquot was removed from the flask and added into a 250 mL Biological Oxygen Demand (BOD) bottle and the respiration rate measured. The rate of respiration was measured over the linear portion of the oxygen consumption trace for an approximate 10 minute period. After measurement, the contents of the BOD flask were returned to the test vessel.

The procedure was repeated after 3 hours contact time.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated laboratory tap water

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: 10, 100 and 1000 mg/L
- Results used to determine the conditions for the definitive study: yes

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

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

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

In the single test vessel prepared by direct dispersion of the test material in water with the aid of ultrasonication to give a test concentration of 21 mg/L (the limit of water solubility supplied by the Sponsor) no significant inhibition of the respiration rate of activated sewage sludge was observed and hence the 3 hour EC50 value was deternnined to be >21 mg/L. Correspondingly the NOEC determined fronn this vessel was 21 mg/L. These results show that at the limit of water solubility of the test material, the test material has no effect on the respiration rate of activated sewage sludge.

The effect of the test material on the respiration rate of activated sewage sludge at concentrations in excess of the water solubility level of the test material was also assessed using a single test concentration of 1000 mg/L prepared by direct dispersion of the test material in water with the aid of ultrasonication. At a test concentration in excess of the water solubility level of the test material, inhibition of respiration of the activated sewage sludge did not occur and the 3 hour EC50 value was deternnined to be greater than 1000 mg/L. Correspondingly the NOEC was determined to be 1000 mg/L.

Results with reference substance (positive control):

The reference material demonstrated the validity of the test system.
3,5-dichlorphenol EC50 14 mg/L

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of the test, at a concentration in excess of the water solubility level of the test material, the test material does not have an adverse effect on the respiration rate of activated sewage sludge. The EC50 was determined to be >1000 mg/L and the NOEC was determined to be 1000 mg/L.

Executive summary:

In a GLP compliant activated sludge respiration inhibition study conducted in line with standardised guideline OECD 209, the effect of the test material on the respiration of activated sewage sludge was determined. Activated sewage sludge was exposed to an aqueous dispersion of the test material at 21 mg/L (limit of test material water solubility) and 1000 mg/L. Under the conditions of the test, the 3 hour EC₅₀ was determined to be >1000 mg/L and the NOEC was determined to be 1000 mg/L.

Description of key information

The 3 hour EC50 of the test material was determined to be >1000 mg/L and the NOEC determined to be 1000 mg/L according to a study performed in line with OECD Guideline 209.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

The test material, at a test concentration in excess of the water solubility level, does not have an adverse effect on the respiration rate of activated sewage sludge.