Menthol

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:

12/1989

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

no

Test organisms (species):

activated sludge

Details on inoculum:

- Initial biomass concentration: 6.0 g/L (dry weight)
- storage of the sludge: aeration of the activated sludge at 20°C ± 2°C, daily fed with synthetic medium
- laboratory scale sewage treatment unit (3L) treating predominantly industrial sewage. (Location: Bürrig / Germany)
- first, the sludge was settled and the supernatant was decanted
- after centrifuging (20 min at 4000 rpm and 20°C) the supernatant was decanted
- approx. 1 g of the wet sludge was dried in order to calculate the amount of sludge to achieve a concentration of activated sludge of 6 g/l (dry weight) suspended solids
- the calculated amount of sludge was first dissolved in synthetic medium and than filled up to a defined end volume with deionised water

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

19.8 °C

pH:

8.0 - 8.3

Dissolved oxygen:

O2 - Start: 5.2 - 8.4 mg
O2 - End: 3.0 - 8.2 mg

Nominal and measured concentrations:

nominal concentrations: (preliminary Test) 100, 1000 and 10000 mg/L
nominal concentrations: (primary test) 100, 180, 320, 560 and 1000 mg/L

Details on test conditions:

Type: aquatic

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

306 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.:

117 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

The concentrations of the test item and reference compound were not confirmed by analytical methods, but instead based on nominal concentrations.
The respiration rate for each concentration was determined graphically from the linear part of the curve of O2-content versus time. The inhibitory effect of the test item at a particular concentration is expressed as a percentage of the mean of the respiration rates of two controls. An EC50 value was calculated, using Probit – analyses, from the inhibition of the respiration rates at different test item concentrations.

Results with reference substance (positive control):

EC50 of the reference compound 3,5-Dichlorophenol is < 20 mg/L

Results:

- preliminary Test:

Test conc. [mg/L]	Respiratory rate [mg/L*h]	Inhibition [%]	Reference substance [mg/L]	Respiratory rate [mg/L*h]	Inhibition [%]
100	22	0	1.0	22	0
1000	3	85	20	5	75
10000	0	100

Results:

- primary Test:

Test conc. [mg/L]	Respiratory rate [mg/L*h]	Inhibition [%]	Reference substance [mg/L]	Respiratory rate [mg/L*h]	Inhibition [%]
100	19	7	1.0	22	0
180	17	19	20	5	75
320	7	67
560	4	80
1000	2	88

Validity criteria fulfilled:

yes

Remarks:

on the basic of graphic evaluation: the EC50 for 3,5-DCP was 20 mg/L and between the prescribed limits of 5 and 30 mg/L.

Conclusions:

For DL-Menthol an EC50 of 306 mg/L was observed.

Executive summary:

A study with activated sludge with a duration of 3 hours was performed according to the OECD Guideline 209. The sludge was exposed to five different concentrations (nominal) of DL-Menthol: 100, 180, 320, 560 and 1000 mg/L. The respiration rate of each mixture was determined after aeration periods of 3 h. An EC10 of 117 mg/L and an EC50 of 306 mg/L was determined by probit analysis.

Description of key information

A study with activated sludge with a duration of 3 hours was performed according to the OECD Guideline 209. The sludge was exposed to five different concentrations (nominal) of DL-Menthol: 100, 180, 320, 560 and 1000 mg/L. The respiration rate of each mixture was determined after aeration periods of 3 h. An EC10 of 117 mg/L and an EC50 of 306 mg/L was determined by probit analysis.

Key value for chemical safety assessment

EC50 for microorganisms:

306 mg/L