5-methyl-5-phenylhexan-3-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:

4th of August 2016 until 9th of October 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

In accordance with GLP

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

natural water

Details on inoculum:

River water was sampled from the Rhine near Heveadorp, The Netherlands (03-08-2016). The nearest plant (Arnhem-Zuid) treating domestic wastewater biologically was 3 km upstream. The river water was aerated for 7 days before use to reduce the endogenous respiration (van Ginkel and Stroo, 1992). River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating.

Duration of test (contact time):

60 d

Initial conc.:

2 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Remarks:

as a percentage of ThOD

Details on study design:

Test bottles:
The test was performed in 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.

Nutrients, stocks and administration:
The nutrient medium of the Closed Bottle test contained per liter of deionized water; 8.5 mg KH2PO4, 21.75 mg K2HPO4, 33.4 mg Na2HPO4·2H2O, 22.5 mg MgSO4·7H2O, 27.5 mg CaCl2, 0.25 mg FeCl3·6H2O. Ammonium chloride was omitted from the medium to prevent nitrification. Accurate administering of the test substance was accomplished by preparing a solid stock of 3.0 mg of the test substance per g of silica gel in a 50-mL serum flask. Only part of the top layer of the silica gel was brought into contact with the test substance. The serum flask was closed with a screw top with aluminium foil and the content was mixed vigorously. Subsequently 0.2 g of silica gel with the test substance was added to the test bottles. The resulting concentration of test substance in the bottles was 2.0 mg/L. Next the bottles were filled with nutrient medium with inoculum and closed. Sodium acetate was added to the bottles using a stock solution of 1.0 g/L.

Test procedure:
Use was made of 10 bottles containing only river water, 10 bottles containing river water and silica gel, 10 bottles containing river water and silica gel with test substance, 6 bottles with river water and sodium acetate. The concentrations of the test substance, and sodium acetate in the bottles were 2.0 and 6.7 mg/L, respectively. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were completely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bottles were closed and incubated in the dark. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.
One extension from the protocol of the Closed Bottle test was introduced. The Closed Bottle test was prolonged by measuring the course of the oxygen decrease in the bottles of day 28 using a special funnel. This funnel fitted exactly in the BOD bottle. Subsequently, the oxygen electrode was inserted in the BOD bottle to measure the oxygen concentration. The medium dissipated by the electrode was collected in the funnel. After withdrawal of the oxygen electrode the medium collected flowed
back into the BOD bottle, followed by removal of the funnel and closing of the BOD bottle (van Ginkel and Stroo 1992).

Test conditions:
The pH of the media was 8.0 at the start of the test. The pH of the media at day 28 was 8.0 (test and controls). Temperatures were within the prescribed temperature range of 22 to 24°C.

Reference substance:

acetic acid, sodium salt

Remarks:

purity > 99%

Test performance:

The validity of the test is demonstrated by an endogenous respiration of 1.3 mg/L at day 28. Furthermore, the differences of the replicate values at day 28 were less than 20%. The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 83. Finally, the validity of the test is shown by oxygen concentrations >0.5 mg/L in all bottles during the test period.

Key result

Parameter:

% degradation (O2 consumption)

Value:

0

Sampling time:

7 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

16

Sampling time:

14 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

24

Sampling time:

21 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

33

Sampling time:

28 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

47

Sampling time:

42 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

69

Sampling time:

60 d

Details on results:

The substance is biodegraded by 33% at day 28 in the Closed Bottle test. The test was prolonged to 60 d, when 69% biodegradation had occurred.
The biodegradation percentage of >60% demonstrates that test substance is inherently biodegradable.

Results with reference substance:

The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 83.

Toxicity to inoculum:

Inhibition of the degradation of a well-degradable compound, e.g. sodium acetate by the test substance in the Closed Bottle test was not determined because possible toxicity of Damascol/4 (mono-constituent) to microorganisms degrading acetate is not relevant.

Inhibition of the endogenous respiration of the inoculum by the test substance at day 7 was not detected. Therefore, no inhibition of the biodegradation due to the "high" initial test substance concentration is expected.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The substance is biodegraded by 33% at day 28 and by 69% at day 60 in the prolonged Closed Bottle test and should therefore be classified as not readily biodegradable. Moreover, a biodegradation percentage of >60 within a 60-day time period allows classification of Damascol (mono-constituent) as not persistent.

Executive summary:

In order to assess the biodegradation of Damascol, a screening test was performed according to OECD TG 301D (Closed Bottle test) and under GLP conditions. In this study river water was exposed to 2 mg/L of the substance for 60 days. Damascol did not cause a reduction in the endogenous respiration. Furthermore, the validity criteria of the test were met.

Damascol was biodegraded by 33% at day 28 and 69% at day 60 in the prolonged Closed Bottle screening test (enhanced biodegradability testing) and should therefore be classified as not readily biodegradable. Moreover, a biodegradation percentage of >60 within a 60-day time period allows categorisation of Damascol (mono-constituent) as not persistent.

Description of key information

The ready biodegradability of Damascol was investigated in a study conducted in accordance with OECD TG 301D (Closed Bottle test) and GLP. The concentration tested was 2 mg/l test substance; river water was used as inoculum. The test substance biodegraded for 33% after 28 days and 69% after 60 days (enhanced biodegradability testing). Damascol was not toxic to the inoculum (83% biodegradation of the sodium acetate reference substance after 14 days). Moreover, a biodegradation percentage of >60 within a 60-day time period allows classification of Damascol as not persistent.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed