6-ethyl-5-fluoro-4(3H)-pyrimidone

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:

From 1999-01-20 to 1999-01-21

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:

yes

Remarks:

The purity was taken to be 92.7% and not 92.3% in error which was not considered to be significant, nor to have affected the integrity of the test.

GLP compliance:

yes

Specific details on test material used for the study:

Batch No.: 960509
Purity: 92.3%

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: an aqueous stock solution of test item (539.4 mg/L) was prepared in dechlorinated tap water and appropriate volumes were added to establish the required test concentration.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Name and location of sewage treatment plant where inoculum was collected: Oakley Sewage Treatment Works
- Method of cultivation: maintained under aerobic conditions until required
- Preparation of inoculum for exposure: On the day of collection, aliquots (25 mL) of the activated sludge were filtered through dried and preweighed Whatman GFC filter papers which were then dried again at approximately 105°C for at least one hour, allowed to cool in a desiccator and reweighed. The mixed liquor suspended solids (MLSS) content of the activated sludge was then calculated. Synthetic sewage (50 mL/L) was added and the mixture aerated overnight.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Hardness:

200 - 250 mg/L as CaCO3

Test temperature:

Initial: 19.8 - 20.8 ℃
Final: 19.6 - 20.6 ℃

pH:

Initial: 7.1 - 7.4
Final: 7.8 - 8.2

Nominal and measured concentrations:

Nominal: 1, 10, 100 mg/L

Details on test conditions:

TEST SYSTEM
- Test volume: 500 mL in total
- Aeration: aerated using a Pasteur pipette connected to a laboratory supply of oil-free compressed air.
- No. of vessels per concentration (replicates): 1 each for 1 and 10 mg/L, 3 for 100 mg/L
- No. of vessels per control (replicates): 2
- Sludge concentration (weight of dry solids per volume): 4 g/L, 16 mL
- Nutrients provided for bacteria: Synthetic sewage feed

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: softened and treated by reverse osmosis (Elga Ltd, Prima 4 reverse osmosis unit) and then purified (Elga Ltd, UHP) to
give a resistivity of 18 Megohm/cm.


OTHER TEST CONDITIONS
- Adjustment of pH: no

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Following the exposure period, a well-mixed sample of each mixture was transferred to a biochemical oxygen demand (BOD) bottle (capacity: 270 mL) and its rate of oxygen consumption over a period of approximately ten minutes was measured using a Yellow Springs Instruments (YSI) dissolved oxygen meter, with temperature probe and self-stirring bottle probe, connected to a chart recorder.
The pH and temperature of the samples were measured at the start and end of the test.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10

Reference substance (positive control):

yes

Remarks:

3,5-DCP

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

The specific respiration rate of the control culture established at the end of the test (41.7 mgO2/g/h) was 92% of the rate of that established at the start (45.5 mgO2/g/h).
The test item had no biologically significant inhibitory effect on the respiration rate of activated sludge at any of the concentrations employed in the test. Respiration rates were decreased by 19 and 14% of the mean control value at nominal concentrations of 1 and 10 mg/L, respectively and were decreased, at most, by 9% in one of three replicates at 100 mg/L.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: 3h-EC50 was 5.9 mg/L (95% confidence limits 4.7 - 7.1 mg/L).

Validity criteria fulfilled:

yes

Conclusions:

Substance had no biologically significant inhibitory effect. The EC20, EC50 and EC80 could not be calculated but must be higher than 100 mg/L.

Executive summary:

The effect of test item on the respiration rate of activated sludge was assessed by the methods detailed in OECD 209.

Samples of activated sludge (suspended solids 1.6 g/L), fed with synthetic sewage, were exposed to the test substance at nominal concentrations of 1, 10 and 100 mg/L for three hours. Single mixtures were prepared at 1 and 10 mg/L and the highest level was prepared in triplicate. Their rates of oxygen consumption were determined and compared with those of controls, containing activated sludge and synthetic sewage alone, which were established at the beginning and end of the culture series.

The test item had no biologically significant inhibitory effect on the respiration rate of activated sludge at any of the concentrations employed in the test. The EC20, EC50 and EC80 could not be calculated but must be higher than 100 mg/L.

Description of key information

The effect of test item on the respiration rate of activated sludge was assessed by the methods detailed in OECD 209.

The test item had no biologically significant inhibitory effect on the respiration rate of activated sludge at any of the concentrations employed in the test. The EC20, EC50 and EC80 could not be calculated but must be higher than 100 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L