1-[2-fluoro-6-(trifluoromethyl)benzyl]-5-iodo-6-methylpyrimidine-2,4(1H,3H)-dione

Toxicity to microorganisms

Administrative data

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

31st May 2018 to 1st June 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: MEP, P.R. China, the Guidelines for the Testing of Chemicals, Effects on Biotic Systems (the Second Edition), No. 209 "Activated Sludge, Respiration Inhibition Test". (2013.8).

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

1-{[2-fluoro-6-(trifluoromethyl)phenyl]methyl}-5-iodo-6-methyl-1,2,3,4-tetrahydropyrimidine-2,4-dione

EC Number:

687-893-6

Cas Number:

1150560-54-5

Molecular formula:

C13H9F4IN2O2

IUPAC Name:

1-{[2-fluoro-6-(trifluoromethyl)phenyl]methyl}-5-iodo-6-methyl-1,2,3,4-tetrahydropyrimidine-2,4-dione

Test material form:

solid: particulate/powder

Sampling and analysis

Details on sampling:

DOC for total respiration was measured for 10 minutes after 3 hours contact time

Test solutions

Details on test solutions:

To prepare test item mixtures, the test item was directly weighed into the test vessel and distilled water was added. Four test concentrations of 10, 100, 300 and 1000 mg/L were prepared.

Test organisms

Details on inoculum:

The activated sludge was derived from a treatment plant receiving predominantly domestic sewage. A fresh sample of activated sludge was collected from the aeration tank of Shenyang North Sewage Treatment Plant 1 day before the test was started and the sludge was fed daily with synthetic sewage feed.

On the day of activated sludge collection, coarse particles were removed by settling for 15mins and decanting the upper layer of fine solids. The sludge was first centrifuged for 5 mins at 2500rpm to produce a clear supernatent. The supernatent liquid was discarded and the sludge resuspended in chlorine-free tap water, and the wash water removed by re-centrifuging for 5 mins and discarding again.
The sludge pellet was resuspended in chlorine free tap water. The concentration of re-suspended sludge was determined by drying 3 replicates of 10ml of suspended at 105 oC for 1hour 50mins. From the measured results, the sludge was further diluted with chlorine-free tap water to obtain the required sludge solids concentration of 3 g/L.

Study design

Test type:

static

Water media type:

freshwater

Total exposure duration:

3 h

Test conditions

Test temperature:

20.2 - 21.6 oC

Nominal and measured concentrations:

The definitive test was conducted with 4 concentrations of 10, 100, 300 and 1000 mg/L. 10, 100, 300 mg/L were tested with 1 replicate, 1000 mg/L was tested with triplicate and an abiotic control at concentration of 1000 mg/L was performed.

Details on test conditions:

Test water: distilled water
Air for aeration: clean oil-free air, flow rate 0.5 ~ 1 L/min

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Results and discussion

Effect concentrations

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

Details on results:

Based on the results of test item test, the EC50 mg/L of test item for total respiration resulted in a total of >1000. Validity criteria were met throughout test.

Results with reference substance (positive control):

3,5-dichlorophenol was used as a reference item in order to check the sensitivity of the activated sludge used as microbial inoculum on the day of exposure. The reference item was tested at 0.5, 1.3, 3.5, 9.4 and 25 mg/L with 1 replicate. Based on the results of the reference item test, the EC50 ( 3 hours) of the reference substance for the definitive test was:
EC50 (mg/L)= 36.5mg/L with a 95% confidence limit of 2.2 ~ 5.6mg/L.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

Based on the results of the test item in the definitive test, the EC50 (3 hours) of test item for respiration is as follows: 

Total Inhibition of respiration EC50 (mg/L) >1000

Executive summary:

The study was conducted to determine the inhibition effects of Methyl iodouracil on micro-organisms from activated sludge (largely bacteria) by measuring their respiration rate. The contact time for exposure was 3 hours. 

The test was conducted with four concentrations of 10, 100, 300 and 1000 mg/L. 10, 100, 300 mg/L were tested with 1 replicate. 1000mg/L was tested in triplicate and an abiotic control at a concentration of 1000mg/L was performed. Inoculums blank controls were performed with 4 replicates. The rate of respiration was determined after 3 hours contact time. 

3,5-DCP was used as a reference item in order to check the sensitivity of the activated sludge used as a microbial inoculum on the day of exposure. The reference item was tested at 0.5, 1.3, 3.5, 9.4 and 25 mg/L with one replicate.

 

The specific oxygen uptake rate of the blank controls (without the test item or reference item) was 21.3 mg/(h·g SS) oxygen. The coefficient of variation of oxygen uptake rate in control replicates was 2.0 at the end of the definitive test. The validity criteria have therefore been satisfied.

Based on the results of the reference test item, the EC₅₀ of 3,5-DCP for total respiration is as follows: 

Inhibition of Respiration	EC50 (mg/L)
Total	3.5

Based on the results of the test item in the definitive test, the EC₅₀ (3 hours) of test item for respiration is as follows: 

Inhibition of respiration	EC50 (mg/L)
Total	>1000