Methyl 2-benzoylbenzoate

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:

February 2015

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

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Identification: RCX 14-672
Chemical name: methyl-2-benzoylbenzoate
Batch no.: N14003
CAS no.: 606-28-0
EC no.: 210-112-3
Molecular formula: C15H12O3
Molecular mass: 240.3 g/mol
Description: white to light yellowish powder
Purity: >99% (gas chromatography)
Water solubility: 117.7 mg/l
Test item storage: at room temperature, protected from light
Stability: stable under storage conditions
Expiry date: 30 November 2015

Analytical monitoring:

not required

Vehicle:

no

Details on test solutions:

The test item was directly weighed into the test vessels containing natural water, in an amount corresponding to achieve the final test concentrations.
A 100-fold concentrated synthetic sewage (32 ml/l of in the final mixture) was then added, followed by the activated sludge suspension (1.7 g/l dry matter in the final mixture).

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Not adapted and not pre-conditioned activated sludge from the aeration tank of the ARA Werdhölzli (CH-8048 Zürich), a municipal biological waste water treatment plant. 1.7 g/l dry matter in the final mixture.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Post exposure observation period:

No post-exposure observation period

Hardness:

Total hardness: 206-242 mg/l

Test temperature:

22 ± 2 °C

pH:

6.9-7.4

Dissolved oxygen:

The oxygen concentration, in mg/l, was measured with an oxygen electrode (ORION 97-08 equipped with an ORION SA 720 transformer; Hügli-Labortec AG, CH-9030 Abtwil). The electrode is inserted into a 300 ml BOD bottle and the oxygen concentration is recorded for up to 10 min.

Salinity:

16.1 mg/l

Nominal and measured concentrations:

Based on the results of the non-GLP preliminary test , with a loading rate of 100 mg/l of RCX 14-672, the definitive test was performed as a screening test with the following loading rates: 100, 316 and 1000 mg/l.

Details on test conditions:

- Test units: 1000 ml flasks containing a total volume of test suspension of 500 ml; aerated by shaking (150 r.p.m.)
- Measuring apparatus: 300 ml flat bottom BOD flasks; polarographic oxygen electrode, connected to a potentio-metric recorder
- Duration/contact time: 3 hours in a temperature-controlled room
- Temperature: 22 ± 2 °C
- Test medium: synthetic sewage feed prepared with tap water:16 ml of 100-fold sewage concentrate per 500 ml of final test mixture

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

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

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

< 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The following respiration inhibition of the activated sludge compared to the blank controls was observed: 10% at 1000 mg/l, 8% at 316 mg/l and 7% at 100 mg/l.

Based on these data, the EC10 value of RCX 14-672 was estimated to be 1000 mg/l loading rate. The EC20, EC50 and EC80 values were all estimated to be >1000 mg/l loading rate. The no observed effect concentration (NOEC) was <100 mg/l as determined by Dunnett’s test.

Results with reference substance (positive control):

The EC50 value of the reference item 3,5-dichlorophenol was estimated to be 5.5 mg/l.

Validity criteria fulfilled:

yes

Executive summary:

The inhibitory effect of RCX 14-672 on the oxygen consumption of activated sludge microorganisms of a municipal sewage treatment plant was investigated under aerobic static conditions over an exposure time of 3 hours. The inhibitory effect may include the effect on respiration and nitrification. The loading rates of RCX 14-672 were 100, 316 and 1000 mg/l.

No chemical analysis of test concentrations was conducted. For the estimation of the effective concentration leading to 10, 20, 50, and 80% respiration inhibition (EC10, EC20, EC50, EC80) the loading rates of the test item were used, assuming the test item to be stable in water over 3 h.

The following respiration inhibition of the activated sludge compared to the blank controls was observed: 10% at 1000 mg/l, 8% at 316 mg/l and 7% at 100 mg/l. Based on these data, the EC10 value of RCX 14-672 was estimated to be 1000 mg/l loading rate. The EC20, EC50 and EC80 values were all estimated to be >1000 mg/l loading rate. The no observed effect concentration (NOEC) was <100 mg/l as determined by Dunnett’s test

Description of key information

The 3-hour EC50 for microorganisms is higher than 1000 mg/L, which is the highest dose level used in the study.

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L

EC10 or NOEC for microorganisms:

100 mg/L