5-methylhexan-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

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study conducted under 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:

activated sludge, domestic, non-adapted

Details on inoculum:

Approximately 4 L of activated sludge was collected from the Wareham, Massachusetts Wastewater Treatment Plant which treats primary domestic sewage. Upon arrival at Springborn. the activated sludge was centrifuged at 1000 rpm for 10 minutes. The supernatant (or secondary effluent) was kept and the solids discarded. The resultant secondary effluent was filtered through coarse filter paper. Following filtration, the first 200 mL of secondary effluent was discarded. The next 500 mL of secondary effluent was retained and aerated. The inoculum was used on the same day as it was prepared.

Duration of test (contact time):

28 d

Initial conc.:

2.5 mg/L

Based on:

test mat.

Initial conc.:

7 mg/L

Based on:

ThOD/L

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

Oxygen-rich water was prepared by bubbling compressed air through water for 20 minutes. Nutrient solutions were prepared using the oxygen-rich water. The nutrient solutions were then aerated for approximately 20 minutes and stored in a refrigerator until used. The water was aerated for an additional 20 minutes and was allowed to stand overnight at 20 ± 1 °C prior to test initiation. Fifty-four industrial 300-mL BOD bottles were prepared for the reference and test substances and the inoculum control blanks; eighteen bottles per treatment, two each for day 0, three per sampling interval (i.e., days 7, 14, 21 and 28) and an additional four bottles for each treatment. The filled BOD bottles were maintained in a dark environmental chamber, set to maintain a temperature of 22 ± 2 °C. A 2.5 mg/L [test substance] solution was prepared by adding 15 mg (18.75 µL) of the test substance directly into 6 L of mineral media. A 10 mg/mL sodium benzoate stock solution was prepared by adding 1.0112 g (1.001 g as a.i.) of sodium benzoate to a flask and diluting to a volume of 100 mL with sterile reagent grade water. The theoretical oxygen demand (ThOD) for the test substance was calculated to be 2.80 mg O2/mg. A nominal test substance concentration of 2.5 mg/L was selected as the test concentration. The test solutions were prepared by first adding approximately 4 L of the aerated water by siphon to each of three 9-L bottles, one for the test substance, one for the sodium benzoate and one for the inoculum control blank. Each 9-L bottle then received 6 mL of each of the four nutrient solutions. The test substance bottle next received 960 µL of the secondary effluent and 18.75 µL of the 2.5 mg/L test substance solution, the sodium benzoate bottle received 960 µL of the secondary effluent and 3.0 mL of the 10 mg/mL sodium benzoate stock solution and the inoculum blank bottle received 960 µL of the secondary effluent. Each of the three bottles was then brought to a final volume of 6 L with the aerated water. Immediately after preparation, each solution was siphoned (bubble-free) from the 9-L bottles into the respective series of 18 BOD bottles (for a total of 54 bottles for the three solution types). The bottles were slightly overfilled to eliminate all air bubbles. Three bottles from each set were labeled for each interval (i.e., days 7. 14, 21 and 28) and two bottles from each set were labeled for day 0. Once filled, the bottles were closed, wrapped in foil and labeled.

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (O2 consumption)

Value:

55

Sampling time:

7 d

Parameter:

% degradation (O2 consumption)

Value:

61

Sampling time:

14 d

Parameter:

% degradation (O2 consumption)

Value:

67

Sampling time:

28 d

Results with reference substance:

Degradation in the sodium benzoate test solutions was greater than 60 % by day 10 and 72 % on day 28 which indicated that the inoculum contained a viable microbial population and that the test procedures used during the study were adequate.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Executive summary:

The determination of the ready biodegradability of methyl isoamyl ketone following OECD Guideline 301 D (Closed Bottle Test) was conducted. 61 % degradation of the test substance occurred by day 14 and 67 % degradation was observed by termination of the 28-day study. The test substance can be classified as readily biodegradable under the conditions of this test.

Description of key information

The determination of the ready biodegradability of methyl isoamyl ketone following OECD Guideline 301 D (Closed Bottle Test) was conducted. 61 % degradation of the test substance occurred by day 14 and 67 % degradation was observed by termination of the 28-day study. The test substance can be classified as readily biodegradable under the conditions of this test.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater