Essential oil of Mentha Spicata L., Erospicata (Labiatae) obtained from aerial parts by steam distillation

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

08 Sep - 06 Oct 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Version / remarks:

(1992)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3100 (Aerobic Aquatic Biodegradation)

GLP compliance:

yes (incl. QA statement)

Remarks:

Staatliches Gewerbeaufsichtsamt, Hildesheim, Germany

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Municipal sewage treatment plant, Hildesheim, Germany (predominantly municipal sewage)
- Storage conditions: aerobic
- Storage length: 6 d
- Pretreatment & preparation of inoculum for exposure: The activated sludge was washed twice with chlorine free tap water. After the second washing the settled sludge was resuspended in mineral salts medium and was maintained in an aerobic condition by aeration for 2 h. Thereafter, the sludge was homogenized with a blender. After sedimentation the supernatant was decanted and maintained in aerobic conditions by aeration with CO2-free air for 6 d. 10 mL/L were used to initiate inoculation.
- Concentration of sludge: 1.13 E09 CFU/L, determined prior to test start by standard dilution plate count
- Initial cell concentration: approximately 1.13 E07 CFU/L in the final test solution

Duration of test (contact time):

28 d

Initial conc.:

19 mg/L

Based on:

test mat.

Initial conc.:

53 mg/L

Based on:

ThOD

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: Mineral salts medium, according to OECD 301 F
- Test temperature: 20.0 - 23.2 °C. Due to technical issues, the temperature dropped from 20 to 11.6 °C for 12 h on Day 21/22.
- pH: 7.61 - 7.63 (at test start); 7.59 - 7.84 (at test end)
- pH adjusted: no
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: brown glass bottles closed with OxiTop measuring heads.
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: aeration with CO2-free air for 6 d
- Measuring equipment: OxiTop measuring heads, WTW
- Details of trap for CO2: A rubber sleeve with soda lime was hung into the opening of the bottles to absorb evolved CO2.

SAMPLING
- Sampling frequency: O2 consumption was dereminded continuously by the OxiTop measuring system at 360 measuring points (every 112 minutes) during the 28 d incubation period

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, containing activated sludge only, 2 replicates
- Functional control: yes, containing inoculum and reference item, 1 replicate
- Toxicity control: yes, containing reference item and test substance, 1 replicate

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (O2 consumption)

Value:

61

Sampling time:

28 d

Details on results:

BIODEGRADATION OF TEST SUBSTANCE
The biodegradation of the test item reached the 10% level (beginning of biodegradation) on Day 5. The course of the degradation was rapid and the mean of test item replicates reached the 60% pass level on Day 17.

After a test period of 28 d, the test item is classified as readily biodegradable as the pass level of 60% biodegradation was reached within the 28 d period of the study. The test item is a UVCB, therefore, the 10 d-window does not apply

TOXICITY CONTROL
In the toxicity control the biodegradation achieved 76% after 14 d. After 28 d the biodegradation reached 84%. The validity criterion that the test item should not inhibit the biodegradation of the reference item was thus fulfilled.

Results with reference substance:

The pass level for ready biodegradability (> 60% degradation) was reached on Day 3. The validity criterion that the degradation should be > 60% after 14 d was fulfilled.

TECHNICAL NOTE:

The climatic exposure cabinet had a technical fault on Day 21 and had to be changed. At that time, both the toxicity control and the functional control had passed their respective validity criteria. Also, the test item replicates had passed the 60% biodegradation threshold. The technical fault resulted in a drop of temperature to 11.6 °C for approximately 12 h. After the change of the cabinet, the prescribed temperature range was restored. Although the exact temperature could not be met again and an offset resulting from the change of the climate exposure test cabinet was observed in the degradation curves, it was concluded that the incident did not affect the integrity and quality of the study.

Biodegradation [%] of the test Test Item in Comparison to the Functional Control and Toxicity Control

[d]	Functional Control	Biodegradation [%] Test item		Toxicity Control (Test Item + Reference Item)
	R1	P1	P2	T1
1	10	0	0	5
2	54	0	0	32
3	67	0	0	40
4	75	0	1	46
5	79	6	14	49
6	81	22	28	56
7	81	30	34	62
8	83	36	37	65
9	84	41	42	68
10	85	44	46	70
11	86	47	48	71
12	86	49	49	73
13	87	51	52	75
14	87	54	56	76
15	88	56	58	77
16	89	57	59	78
17	90	59	61	79
18	90	61	63	80
19	91	61	63	80
20	91	62	65	81
21	92	64	66	82
22	93	64	65	83
23	87	54	60	81
24	87	54	60	81
25	87	56	62	83
26	87	56	62	83
17	88	56	63	83
28	88	57	64	84

R1        = functional control

P1, P2 = test substance, replicates 1 and 2

T1         = toxicity control

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Description of key information

Readily biodegradable, 61% in 28 d (OECD 301 F, non-adapted activated sludge)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

There is one GLP certified study available, which assessed the ready biodegradability of the test substance according to the OECD guideline 301 F.

Non-adapted activated sludge from a local wastewater treatment plant treating predominantly municipal sewage was inoculated with a nominal concentration of 19 mg test substance/L for 28 d in controlled, aerobic conditions in the dark. A functional control and a toxicity control were run in parallel. The biodegradation of the test substance in % was followed by measuring the oxygen concentration in the test vessels continuously. The biodegradation rate was calculated and expressed as the percentage BOD with respect to the ThOD (2.79 mg O2/mg test item).

The toxicity control indicated that biodegradation by activated sludge was not inhibited by the test substance. The mean biodegradation on Day 28 was 61%. Since the test substance is a UVCB the 10 d-window does not apply. Therefore, the test substance was classified as readily biodegradable as the pass level of 60% biodegradation was reached within 28 d.