4-methyl-4-phenylpentan-2-one

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:

28 Feb - 29 Mar 2017

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:

17 Jul 1992

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Version / remarks:

30 May 2008

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3110 (Ready Biodegradability)

Version / remarks:

1998

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Swiss Federal Office of Public Health, Consumer protection directorate, Notification authority for chemicals, Bern, Switzerland (16 Dec 2015)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: aeration stage of the local wastewater treatment plant, ARA Birs, Birsfelden, Switzerland
- Storage conditions: During the holding period of 1 d prior to use, the sludge was aerated at room temperature.
- Storage length: 1 d
- Preparation of inoculum for exposure: The aerobic activated sewage sludge was washed three times by centrifugation, decantation of the supernatant liquid phase and resuspension of the solid material in tap water and finally in mineral medium. Aliquots of the homogenized final sludge suspension were weighed, thereafter dried and the dry weight of the suspended solids was determined.
- Concentration of sludge: Based on the measured dry weight of the suspended solids, a calculated amout of wet sludge was suspended in mineral medium to obtain a concentration equivalent to 4 g dry material per liter, which was stored during 1 d. Prior to use, the dry weight of the sludge was again determined and the sludge was diluted approximately 1:4 with mineral medium. Defined volumes of this diluted activated sludge were then added to the mineral medium in the test vessels to obtain a final concentration of 30 mg dry material per liter.

Duration of test (contact time):

28 d

Initial conc.:

100 mg/L

Based on:

test mat.

Initial conc.:

281 mg/L

Based on:

ThOD

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: Mineral medium according to guideline
- Test temperature: 22 - 23 °C
- pH: 7.4 (test start), 7.1 - 7.8 (test end)
- pH adjusted: The pH of the mineral medium was adjusted from 7.8 to 7.4 with a diluted hydrochloric acid solution.
- Suspended solids concentration: 30 mg dry material/L (final concentration)
- Continuous darkness: The test vessels were incubated under diffused lighting.
- Other: The test was conducted in a thermostatic cabinet.

TEST SYSTEM
- Culturing apparatus: GL45 laboratory glass bottles with a nominal volume of 500 mL.
- Number of culture flasks/concentration: 2
- Measuring equipment: OxiTop Control system from WTW GmbH, Weilheim, Germany consisting of pressure measuring heads, test bottles, an inductive stirring system and the OxiTop OC 110 Controller.
- Details of trap for CO2 and volatile organics if used: Carbon dioxide was absorbed by sodium hydroxide pellets.
- Other. The prepared test vessels were closed air-tight with the OxiTop measuring heads.
- Other: The test temperature was recorded throughout the study at least on each working day. The pH was measured prior to the start of the test (Day 0) in each test vessel before the addition of the inoculum. At the end of incubation, the pH was measured again in every test vessel.
- Approximately 16.4 mg test item were added to the designated test vessels with mineral medium. No emulsifiers or solvents were used. Finally, activated sludge was added to each test vessel. The final test volume was 164 mL per test vessel.

SAMPLING
- Sampling frequency: The pressure reduction was continuously detected by the OxiTop pressure measuring heads and recorded every 3 h.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Mineral medium only (2 replicates)
- Toxicity control: 100 mg/L test item (ThOD: 281 mg/L) + 100 mg/L reference item (ThOD: 167 mg O2/mg) in mineral medium (1 replicate).
- Procedure control: 100 mg/L reference item (ThOD: 167 mg O2/mg) in mineral medium (2 replicates).

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (O2 consumption)

Value:

29

Sampling time:

28 d

Remarks on result:

other: mean value of two replicates

Results with reference substance:

After 28 d, the average biodegradation of the procedure control with the reference item sodium benzoate was 89% (2 replicates).

BIODEGRADATION OF THE TEST ITEM

The oxygen consumption of the test item in the test media was in the range of the oxygen consumption in the inoculum controls during more than half of the exposure period of 28 d. A detectable biodegradation of the test item started after approximately 18 and 16 exposure days in replicate 1 and 2, respectively. Although the biodegradation started a few days earlier in replicate 2 than in replicate 1, replicate 2 reached a lower biodegradation of 19% compared to 39% in replicate 1 after 28 d.

The mean biodegradation of both replicates is 29% after 28 d. The start of the 10 -day window was on exposure Day 20 and therefore, the window was not completed at the end of the test.

The pass level for ready biodegradability, i.e. biodegradation of at least 60% of the ThOD in a 10-d window within a 28-d period, was not reached.

BIODEGRADATION OF THE REFERENCE ITEM

In the procedure control, the reference item was degraded by an average of 71% and 85% by exposure Days 4 and 14, respectively. Thus, the suitability of the activated sludge was confirmed (≥ 60% degradation by exposure Day 14). By the end of the test on Day 28, the average degradation was 89%.

BIODEGRADATION IN THE TOXICITY CONTROL

In the toxicity control, the oxygen consumption during the 28-d exposure period correlated with the oxygen demand of the two added substances, i.e. the test item and the reference item. Biodegradation reached 33% after 14 d and 63% after 28 d. Therefore, according to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the test concentration of 100 mg/L because biodegradation in the toxicity control was > 25% within 14 d of incubation.

Table 1. Biodegradation of the test item and the reference item sodium benzoate during the incubation period.

Time [days]	Percent Biodegradation^1
	Test item		Procedure control			Toxicity control
	Replicate n°		Replicate n°			Replicate n°
	1	2		1	2		1
0	0	0		0	0		0
1	0	0		19	19		9
2	0	0		46	46		19
3	1	1		55	62		24
4	0	0		70	72		27
5	0	0		75	76		30
6	1*	0		76	77		30
7	0	0		79	80		31
8	0	0		80	81		31
9	0	0		81	82		32
10	0	0		82	84		32
11	0	0		83	83		32
12	0	0		84	84		33
13	0	0		84	85		33
14	0	0		85	86		33
15	0	1		85	87		34
16	0	1		85	87		34
17	1	6		85	88		37
18	2	10		85	87		40
19	3	12		86	89		41
20	5	14		87	89		43
21	8	17		86	88		45
22	16	17		86	88		47
23	27	18		87	89		50
24	32	18		88	89		53
25	35	18		88	89		56
26	37	18		89	90		58
27	37	18		89	89		60
28	39	19		88	89		63
Mean (Day 28)	29			89			Not applicable

¹Corrected for the mean oxygen uptake of the inoculum controls

^*Negative value due to higher oxygen consumption in the inoculum controls than in the test vessel with test item.

VALIDITY CRITERIA

The results are considered valid. All validity criteria were met, except the one stated here below:

"The difference of the extremes of replicate values of the degradation of the test item at the end of the 10 -day window, at the time the plateau is reached or at the end of the test, as appropriate, is less than 20%."

Despite homogenization, the inoculum in each replicate may include a variable range of microorganisms. During the adaptation phase a further selection of only the microorganisms, which are able to actively degrade the test item, i.e. to use the test item as sole source of organc carbon, occurs. Therefore, it is possible that, after a long lag phase, adaptation and growth of the microorganism population in the different replicates occurs unequally.

The differences in the biodegradation patterns of the replicates in the present test reflect the unequal adaptation of inocula with slightly different microorganism community composition to the test item.

At the end of the 28-d exposure period, the 10-d window was not completed and a plateau of the biodegradation curve was reached at a considerably lower level than 60%.

It is assumed that a repetition of the test would not change the main result of the study.

Validity criteria fulfilled:

yes

Remarks:

For further details please refer to “Any other information on results incl. tables”.

Interpretation of results:

not readily biodegradable

Conclusions:

The Manometric Respirometry Test showed that the test item is not readily biodegradable after 28 d exposure to activated sludge, according to the guideline criteria (OECD 301 F).

Description of key information

Not readily biodegradable: 29% after 28 d (O2 consumption, OECD 301F)

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Additional information

One GLP guideline study according to OECD 301 F is available investigating the ready biodegradability of the substance. Non-adapted, domestic activated sludge from a sewage treatment plant was used as inoculum with a nominal concentration of 100 mg/L test substance (corresponding to 281 mg/L based on ThOD) and incubated for 28 d under diffused lighting. Degradation was followed by the determination of dissolved oxygen content every 24 h. An inoculum blank, a procedure control (with 10.0 mg reference substance/L) and a toxicity control were run in parallel. The degradation rate was 29% for the test substance and 89% for the reference substance after 28 d. The toxicity control attained 33% degradation after 14 d indicating that the substance is not inhibitory to the inoculum. Since the test substance did not reached the pass level for ready biodegradability of > 60% removal of ThOD within 28 d it is not readily biodegradable according to the OECD criteria.