Thymol

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

JAN 1986 - MAR 1986

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

GLP compliance:

no

Specific details on test material used for the study:

- solid

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly industrial sewage

Details on inoculum:

- Source: OECD-facility
- Method: First, the sludge was settled and the supernatant was decanted. After centrifugation (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 wet 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 then 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

Remarks on exposure duration:

with permanent aeration

Test temperature:

22 °C

pH:

7.3 - 7.4

Nominal and measured concentrations:

nominal concentrations: 1.6, 3.2, 6.3, 12.5, 25 and 50 mg/L

Details on test conditions:

Type: aquatic
- test concentration of activated sludge: 0.30 g/L (dry weight)
- test vessels: 300 mL glass Erlenmeyer flasks, filled volume 250 mL

Reference substance (positive control):

yes

Remarks:

3.5-dichlorphenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

39.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: 31.8 - 55.1 mg/L

Details on results:

The concentrations of the test item and reference compound were not confirmed by analytical methods.

Results with reference substance (positive control):

EC50 of the reference compound 3.5-Dichlorophenol is in the range 5 - 30 mg/L.

Substance	Amount of test solution mL	Concentration mg/L	Amount nutrition medium mL	Respiration rate mg/mL min O2	% Inhibition
Thymol	125	50	8	0.15	60.53
	62.5	25	8	0.27	28 .95
	31.2	12.5	8	0.35	7.90
	15.6	6.3	8	0.35	7.90
	7.8	3.2	8	0.36	5.27
	3.9	1.6	8	0.41	0
3.5 -Dichlophenol	50	100	8	0	100
	0.5	1	8	0.35	7.90
1. Control	-	-	8	0.37	-
2. Control	-	-	8	0.4	-
Mean Control	-	-	-	0.38	-
Endogen	-	-	-	0	-

Validity criteria fulfilled:

yes

Remarks:

The respiratory rates of the 2 controls differ less than 15 % and the EC50 of the reference compound 3.5-Dichlorophenol is in the range 5 - 30 mg/L.

Conclusions:

An 3h-EC50 of 39.6 mg/L was observed.

Executive summary:

The toxicity of thymol to activated sludge was investigated according to OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test). An 3h-EC50 of 39.6 mg/L was determined.

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is found to be readily biodegradable and the applied test concentrations are in the range of concentrations that can be expected in the influent of a sewage treatment plant

Description of key information

According to column 2 of REACH Annex VIII, an activated sludge respiration inhibition test does not need to be conducted as the substance is found to be readily biodegradable and the applied test concentrations are in the range of concentrations that can be expected in the influent of a sewage treatment plant. Nonetheless, the values derived from an OECD 209 guideline test have been used for risk assessment.

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test), 3h, activated sludge, result: 3h-EC50 of 39.6 mg/L was observed (Bayer AG, 1986), which was re-written at Currenta in 2009.

Key value for chemical safety assessment

EC50 for microorganisms:

39.6 mg/L