1,4-naphthoquinone

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

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 (Carbon and Ammonium Oxidation))

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

no

Details on test solutions:

Test substance stock solutions: A 200 mg sample of the test substance was ground in a mortar and dissolved in ultra pure water (2 L). This was stirred for 5 minutes, sonicated for 5 minutes to prepare a 100 mg/L stock solution.
Reference substance stock solution: A 200 mg sample of DCP dissolved in ultra pure water (200 mL, 1000 mg/L). This was then used to prepare a 100 mg/L stock solution.
Nitrification inhibitor stock solutions: A 464 mg sample of ATU was dissolved in ultra pure water (200 mL, 2320 mg/L).

The pH of all above stock solutions were checked and adjusted by adding NaOH and H2SO4 to pH 7.5 ± 0.5.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Activated sludge sourced from a domestic sewage treatment plant. Sludge collected 2 days before exposure and stored aerated at 20 ± 2°C. The MLSS was determined to be 2970 mg/L with a pH of 7.5 ± 0..5. The sewage was collected without sieving and washing. The synthetic sewage feed was added on the day of collection The MLSS was adjusted to 3000 mg/L on the day of exposure.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Hardness:

Not determined

Test temperature:

20.2 to 20.3°C (in water tank)

pH:

Controls: Start 7.2, end 7.9 to 8.
Test mixtures: Start 7.2 to 7.3, end 7.8 to 8.
Reference mixtures: 7.2 to 7.3, end 7.8 to 8.

Dissolved oxygen:

Varies per vessel and is main endpoint assessed

Salinity:

Not determined

Conductivity:

Not determined

Nominal and measured concentrations:

Test solutions: 0.1, 0.42, 1.7, 7.2 and 30 mg/L
Reference mixtures: 0.1, 0.5, 3.2, 18 and 100 mg/L

Details on test conditions:

TEST SYSTEM

See 'other information on materials and methods incl. tables' for full details.

- Test vessel: 1000 L (glass)
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: 500 mL
- Aeration: Yes
- Sludge concentration (weight of dry solids per volume): 30 mg/L
- Nitrification inhibitor used: N-allylthiourea

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Ultra pure water

OTHER TEST CONDITIONS
- Adjustment of pH: Test stock solutions adjusted
- Photoperiod: Light for 3 hours

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Respiration inhibition based on DO.
TEST CONCENTRATIONS
- Range finding study: Conducted at 0.01, 0.1, 1, 10, 100 and 1000 mg/L. This showed high respiration inhibition at > 1 mg/L.
- Test concentrations:0.1, 0.42, 1.7, 7.2 and 30 mg/L
- Results used to determine the conditions for the definitive study: Yes

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol (DCP)

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

5.94 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

4.84 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of heterotrophic respiration

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

9.16 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

1.72 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

1.28 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of heterotrophic respiration

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

3.42 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of respiration due to nitrification

Details on results:

The average inhibition rates at the relevant concentrations are as follows:
Average inhibition (total respiration): -7.2, 9.2, 9.2, 59.6 and 94.7% (at 0.1, 0.42, 1.7, 7.2 and 30 mg/L, respectively).
Average inhibition (heterotrophic respiration): 6.7, 9.6, 14.7, 67 and 95.3% (at 0.1, 0.42, 1.7, 7.2 and 30 mg/L, respectively).
Average inhibition (nitrification respiration): -46.2, 8.1, -6.6, 39.3 and 93.4% (at 0.1, 0.42, 1.7, 7.2 and 30 mg/L, respectively).

The specific respiration rate of the controls was 28.1 mg oxygen per gram of activated sludge (dry weight of suspended solids) in an hour.
The CoV of oxygen consumption rate in control replicates was 9.7%

Results with reference substance (positive control):

The EC50 of DCP was 10.9, 12.6 and 2.26 mg/L for total, heterotrophic and nitrification respiration, respectively. This is within the guideline ranges indicating the test is valid.

Reported statistics and error estimates:

ECx: If the percentage inhibition is greater than 50%, the EC50 value is calculated using a probit method, which was conducted in this case (Ecotox Statics ver.2.6d)
NOEC: This was not determined as the EC50 was determined.

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of an ASRIT study conducted in accordance with the OECD 209 guideline, 3 hour EC50 values of 5.94, 4.84 and 9.16 mg/L were determined for total respiration, heterotrophic respiration and nitrification respiration, respectively. No NOEC was determined but EC10 values are available.

Description of key information

Under the conditions of an ASRIT study conducted in accordance with the OECD 209 guideline, 3 hour EC50 values of 5.94, 4.84 and 9.16 mg/L were determined for total respiration, heterotrophic respiration and nitrification respiration, respectively. The value for total respiration is selected as the key value for chemical safety assessment. No NOEC was determined but EC10 values are available. The EC10 value for total respiration has been included as the key value for chemical safety assessment.

Key value for chemical safety assessment

EC50 for microorganisms:

5.94 mg/L

EC10 or NOEC for microorganisms:

1.72 mg/L