diisopentylphthalate

Biodegradation in water: screening tests

Administrative data

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

10 Sep 2010 - 12 Aug 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2011

Report date:

2011

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Diisoamyl phthalate

IUPAC Name:

Diisoamyl phthalate

Details on test material:

- Name of test material (as cited in study report): Diisoamyl phthalate

- Substance type: organic
- Physical state: liquid
- Analytical purity: 100%


- Lot/batch No.: 7920-1-1
- Expiration date of the lot/batch:12 August 2012

- Storage condition of test material: room temperature in the dark
- Other

Study design

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge (adaptation not specified)

Details on inoculum:

A sample of activated sludge was obtained from Worlingworth sewage treatment works, which treats predominantly domestic waste. At the time of collection, the sludge was sieved (1 mm2) then transported to the laboratory and left to stand for approximately 30 minutes to allow the sewage solids to settle. A portion of the supernatant was removed and the sludge aerated until required.
The concentration of suspended solids in a homogenised sample was determined before the start of the test. Aliquots (10 mL) of the sludge were filtered through dried and preweighed Whatman GF/C filters, which were then dried again at approximately 105°C for one hour, allowed to cool in a desiccator and reweighed. The mixed liquor suspended solids (MLSS) content of the sludge was then determined and the volume required to give a solids level of 30 mg/L in test cultures was calculated. This was added to flasks two days before test initiation to allow a period of ageing.

Duration of test (contact time):

ca. 28 d

Initial test substance concentration

Initial conc.:

ca. 47.94 mg/L

Based on:

ThOD

Parameter followed for biodegradation estimation

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

In this test, a Co-ordinated Environmental Services (CES) Ltd automated respirometer and associated software was used to monitor the cumulative amount of oxygen consumed by the mixtures.
Two days before test initiation, a volume (6 litres) of mineral salts medium was prepared and the pH determined and adjusted to 7.6 with 5M HCL Appropriate volumes of the MSM were then added to six glass culture bottles (500 mL) and inoculated with activated sludge. Magnetic stirrer bars were added to the cultures and each bottle was fitted with an electrolytic cell (containing the electrolyte, IM copper sulfate solution, and the CO2 absorber, 5 mL of 2M potassium hydroxide) and connected to the respirometer. A magnetic stirrer was set to give a vortex in each test mixture and the instrument was initiated.

Information provided by the Sponsor indicated that the test substance was insufficiently soluble in water to prepare a stock solution. Therefore, at test initiation (Day 0), the test substance (nominally 20.4 mg) was added directly as a volume (20 µL) to each test bottle to give a final nominal concentration of 47.94 mgOi500 mL or 95.9 mgO2/L.
Sodium benzoate (20 mL) was added as an aqueous stock solution (0.750 g/L) in MSM to the
reference and inhibition assay cultures to give a final nominal concentration of 50 mgO2/L or 25 mgO2/500 mL.
The pH of the cultures was measured and no adjustment was necessary.
The CO2 absorber was replaced in each cell (to ensure the maximum adsorption capacity in the test) and the cultures were sealed and returned to the water bath to equilibrate. The cells were connected to the computer-controlled system and the test was initiated.
A record of the cumulative oxygen demand made by each cell was printed at hourly intervals.
The correct operation of the magnetic stirrers and the temperature of the water bath were recorded at appropriate intervals during the test.
On Day 28 the test was halted and the pH of each mixture was measured.

Reference substance

Reference substance:

benzoic acid, sodium salt

Results and discussion

Test performance:

Information provided by the Sponsor indicated that the test substance was insufficiently soluble in water to prepare a stock solution. Therefore, at test initiation (Day 0), the test substance (nominally 20.4 mg) was added directly as a volume (20 µL) to each test bottle to give a final nominal concentration of 47.94 mgOi500 mL or 95.9 mgO2/L.

Sodium benzoate (20 mL) was added as an aqueous stock solution (0.750 g/L) in MSM to the
reference and inhibition assay cultures to give a final nominal concentration of 50 mgO2/L or 25 mgO2/500 mL.

The pH of the cultures was measured and no adjustment was necessary.
The CO2 absorber was replaced in each cell (to ensure the maximum adsorption capacity in the test) and the cultures were sealed and returned to the water bath to equilibrate. The cells were connected to the computer-controlled system and the test was initiated.
A record of the cumulative oxygen demand made by each cell was printed at hourly intervals.
The correct operation of the magnetic stirrers and the temperature of the water bath were recorded at appropriate intervals during the test.

On Day 28 the test was halted and the pH of each mixture was measured.

% Degradation

Key result

Parameter:

% degradation (O2 consumption)

Value:

ca. 75

Sampling time:

28 d

Remarks on result:

other: Mean oxygen consumption in mixtures containing diisoamyl phthalate was equivalent to 10% of the theoretical value after approximately 3 days, 60% after approximately 12 days and 75% at the end of the test on Day 28.

Details on results:

The blank-corrected oxygen demanded by the culture containing the reference substance had achieved 15.68 mgO2/500 mL or 63% of the ThOD (25 mgOz/500 mL) after 3 days of incubation and 24.00 mgO2/500 mL or 96% by Day 28. In the presence of diisoamyl phthalate, degradation of sodium benzoate had achieved 62% by Day 3. Cumulative levels of oxygen consumption by the controls after 28 days (14.28 and 10.53 mgOz/500 mL, equivalent to 28.56 and 21.06 mgO2/L) were considered to be acceptable for this assay system. These results confirm that diisoamyl phthalate was not inhibitory to the activity of the microbial inoculum and that the test was valid.
Mean oxygen consumption in biotic mixtures containing diisoamyl phthalate was equivalent to 10% of the theoretical value (47.94 mgO2/500 mL) after approximately 3 days, 60% after approximately 12 days and 75% at the end of the test (Day 28).
Substances are considered to be readily biodegradable in this type of test if oxygen consumption is equal to or greater than 60% of the ThOD of the test mixtures within ten days of the consumption achieving 10%. Therefore, diisoamyl phthalate was considered to be readily biodegradable under the conditions of this test.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

Mean oxygen consumption in mixtures containing diisoamyl phthalate was equivalent to 10% of the theoretical value after approximately 3 days, 60% after approximately 12 days and 75% at the end of the test on Day 28.
Substances are considered to be readily biodegradable in this type of test if oxygen consumption is equal to or greater than 60% of the theoretical value within ten days of the level achieving 10%. Therefore, diisoamyl phthalate was considered to be readily biodegradable under the conditions of this test.
The results obtained for the rate of degradation of sodium benzoate (63% of its ThOD after 3 days) and for the cumulative amount of oxygen consumed by the control mixtures (28.56 and 21.06 mgO2/L) fulfil the validity criteria for this test.
In the presence of diisoamyl phthalate the degradation of sodium benzoate achieved 62% after 3 days indicating that the test substance was not inhibitory to the microbial inoculum.